Hello, I'm Marilyn Kaplan. I'm out of Albany, New York, an historic architect. I'll be joined in this session with Mike Jackson, another historic architect from Springfield, Illinois. We are the co-chairs of the APT or Association for Preservation Technology Technical Committee on Codes and Standards, and our talk today is on an overview of codes relating to historic buildings or using codes to save buildings. The agenda for today's session is some background on historic preservation, on building codes, on the model codes. We're going to talk about housing and property protection, and then code advocacy. A few definitions before we start. We will be talking a lot about the model codes. What these are in the context of this talk are construction codes. They are developed and maintained by a standards organization independent of local or state jurisdictions, and they are only enforceable when they're adopted by the jurisdiction. The International Code Council since 2002 has been the primary organization publishing the U.S. Construction Codes. The International Existing Building Code, or the IEBC, or the 2021 version, they date back to 2003. You'll hear quite a bit of reference to that. And we'll be talking about, of course, historic buildings. And the definition in the context of the existing building code for the historic building provisions are that we have a building that's listed or eligible for historic designation in the National Register for Historic Places, not local eligibility. That's an important distinction, designated as historic under applicable state or local law, or a building that contributes to a national state or local historic district. So what that really means is that it's not sufficient to use the historic building provisions if a building has only been declared locally eligible. A bit of background on historic preservation. Many of you, of course, are familiar with much of this. 1853, the Mount Vernon Ladies Association organized to save George Washington's home. 1931, the first historic district, the open historic Charleston Historic District in South Carolina. Probably the heyday, early heyday for historic preservation in the U.S. were in preparation of the bicentennial between 1966 and 1976, passage of the National Historic Preservation Act. Many states soon after received their own State Historic Preservation Acts, listing on the National Register of Historic Places, the publication of the Secretary of the Interior standards for the treatment of historic properties. And of course, since 1976, the Federal Preservation Tax Incentives. The tax incentives have been a wildly successful federal program. This is last year's annual report from the National Park Service. And you can see on the right huge numbers of projects that have been undertaken, low and moderate income, new housing units, rehabilitated housing units, $116 billion. So, a little bit more detail background on building regulations. It's hard to start a talk without speaking to the earliest known code, Hammurabi. 1755-ish BC. We consider it related to health, safety, and welfare as are the modern codes, but really it's a bit of an eye for an eye and a tooth for a tooth. And there's quite a bit of accountability and responsibility related to building construction in that code. Jump forward hundreds and hundreds of years, and the earliest codes in the U.S. dealt with the protection of property and the means of production. The earliest building code, 1905, intended to create sprinkler standards in the Northeast, where there were hundreds and hundreds of mills that had early sprinklers, but none of them were standardized. And so this was an attempt by the insurance underwriters to create a standardized code to protect these mill buildings and their production. The map on the right is the National Historic Preservation Act, and you can see the number of mills there from the 19th century. Later local ordinances and some codes dealt with major conflagrations, which had the capacity to spread very, very rapidly through cities. As a result, creation of fire districts, which through zoning or other ordinances restricted the types of activities that could occur in certain areas of the city. Many, many fires and major fires, we mostly talk about the Great Chicago Fire, but in Boston, 1872, you can see in the bottom left the scale of the city or the area of the city that was damaged. But there was a building act and following this code, and it established tight restrictions, firewalls between buildings, the types of materials and dimensions that could be used, where windows and doors could go, restrictions on smoke pipes and chimneys and closing furnace rooms, and established fines. Many, many fires and the impacts of those fires make their way into the codes, one of the ones that's very well studied is the Triangle Shirtways Factory in New York City. This is an interesting fire, it's a deadly industrial fire, 146 mostly immigrant women garment workers died, primarily related to locked exits in the buildings. And the code follow ups were a pamphlet outside stairs for fire exits and eventually the building exits code, which became incorporated into some of the National Fire Protection Association documents. This fire was very interesting as well because there's a large labor movement that moved to protect the workers for the first time and not just the products of what was being produced. The history of major disasters continues and impacted the codes all the way up to today, to yesterday, to tomorrow, 1992, for Cain Andrew, thousands and thousands of buildings devastated, 250,000 people homeless. The code follow up were hardening those buildings in the areas in particularly South Florida, initially for roofing, wind and impact resistance and talking about code enforcement. Much more recently, the 2017 Grenfell Tower fire in West London, and this was a horrific fire, 35 story building, single exits. Oddly enough, it was a energy retrofit project that had recently occurred and a lot of the devastation of the fire was a result of some of the exterior enclosure to that, a devastating, devastating fire. Forest fires and wildfires just last year's 2021 Dixie fire in California. At that point, second largest fire in California history, 63,000 acres, more than 1,000 buildings lost and life lost. And look at the impact on Main Street, lower left. This year's big fire at Twin Parks in New York City, 17 people died. And what did we find out that the door closers in the apartments malfunctioned? And that was a means for the fire to readily travel through the building. Oddly enough, this was a model urban renewal project, so this probably speaks more to code enforcement than to other substandard conditions. We'll get back to that. More recently, we're seeing all of the codes reflect to some of these current issues, wildfire and earthquakes and climate change, and we'll continue to see the codes evolve and change. Wildfires, these are in Wyoming. Again, look at the impact, not just in that remote rural area, but also as that fire spreads into the community and totally destroys what is the heart of that community. Here's not a wildfire, but a major fire in a building. And again, totally destructive of the integrity of that Main Street, the adjacent buildings, and of course that buildings is lost. This has happened in all of our communities. So in studying the history of fire, we can see more than 100 years of shifting priorities. We go from fire, we see environmental concerns, 1970s and forward energy codes, accessibility codes. And more recently, 2020s, seismic codes, sea level rise, wildfires. The codes deal with all of these issues, which is rather complex and rather demanding on buildings that may be 100 or 150 years old. So let's talk about the codes themselves. Prior to 1997, there were three primary model code organizations regionally organized. In the northeast, we had BOCA. In the southeast, the Southern Building Code Congress. And in the west, or say, west of Mississippi, we had the Uniform Building Code. Three different organizations formed from the 1920s through the 1950s. We also have as a major, or 1940s rather, we also have as a major player, the National Fire Protection Association. You've been introduced to them already formed in 1896 through the insurance industry. But in 1994, that all began to change. The International Code Council was formed. It's really a national organization, although some of their documents and resources extend internationally. It was formed by those three model code organizations, and they began to publish their own codes, absorbing the model code organizations. Their first code was the 1997 plumbing code. And since then, the International Code Council, or the ICC has published 15 separate codes. Again, these are model codes until they're adopted by a state or by a locality. These are very technical documents. They're typically reissued on three-year cycles. They are influenced by architecture and engineering and public policy, construction, building science, industry, labor, research, technology, catastrophes. We just saw public expectations for safety, precedence, cost, benefit, and to a small degree historic preservation. The codes we're most interested in the context of existing and historic buildings are the building code, the fire code, the existing building code, and the energy conservation code. The property maintenance code is also something we're going to talk quite a bit about at the conclusion of this session. So of those model codes, one can follow the paths established in the residential code for residential buildings, the existing building codes for any occupancy, or the building code, which isn't generally intended for non-residential occupancies that don't meet the provisions, the one or two family or the townhouses of the residential code. It doesn't address rehabilitation, but in many communities it's the only code that's been adopted or you've got code officials or architects or contractors who are most familiar with it. We're strong proponents of the existing building code, which has been written for existing buildings and historic buildings, and a lot of the talk today will speak to the code paths established in that document. Just a very quick comment on codes and the construction process for those who may not be familiar. So if you're in a community, a state, a locality that has adopted codes and enforcement, it is typically the role of the architect or the engineer to prepare the construction documents, which is used for permitting. The documents must show that they're compliant with the codes that have been locally adopted. This process may or may not be required for all project types. For example, residential in some states are not covered by the permitting process. There are questions of the type of rehabilitation project. If you're working on an existing building, is it a repair? Is it an alteration? Is it a change of occupancy? But all of that information is contained in the technical documents, the drawings themselves. Those documents are submitted to the code official, as where it's required, any modification requests are made, modifications as requested are made, and a building permit is issued. In larger communities, there may be internal processes that coordinate the permitting process with zoning, historic or design review commissions, and or coordination with the fire code. During construction, there may be special inspections at the time, for example, the foundation's report or insulation is installed or the electrical work is roughed in, but that's a function of how each community works. And when the project is all done, the certificate of completion or certificate of occupancy is issued. So that's how the codes generally fit into this whole process of construction. I'm going to give the stage, there's no stage, of course, to my colleague here, Mike Jackson, and he'll be talking about the model codes, in particular the existing building code, historic residential buildings, and also adoption and local modifications. Thanks, Marilyn, for getting us started today. I'm going to take a little deeper dive into the existing building code and some of the provisions related to historic buildings, but it really starts here. Our goal is to make buildings safer, while preserving their authenticity. And this statement, I'm going to read it to you from the energy code, says that when demonstrating that compliance with provisions would threaten, degrade or destroy the historic form, fabric, or function of the building. That's the key that we want to avoid. We have to demonstrate, we have to understand what our building is, what are the features, and if this fits, then we're going to take alternative actions. But we want to make our building safer, and we want to preserve their authenticity. Building codes started the look of our downtowns and our many of our historic communities. In the 19th century, fire districts were set up that said no wood frame buildings in the center of our cities, because we were concerned about the common fact that urban centers burned, Boston and Chicago being two of the more noteworthy of these. And it worked largely. We don't hear about cities burning down anymore if fires are more contained and they don't spread. And now the issue is more in the rural areas in the urban wildfires around cities, but this has largely worked. The codes then moved on from fire safety into other health issues. And in the late 19th century, sanitary conditions of plumbing came in and then natural light and ventilation. The urban apartment building on the left is the Tenement Museum in New York City. An excellent example of that 19th century tournament and tenement and the need for good natural light and ventilation and uncrowded sanitary conditions. The first national building code came from the fire insurance underwriters focused on fire safety. It was in 1905. By the 1920s, we had an interesting turn of event as different code model code organizations are coming into play. And in the 1927 edition of the Uniform Building Code, a provision was inserted that said if you spent more than 50% of the value of an existing building, then any renovation you had to do had to make it equal to a new building. This kind of prejudice that cost expenditures triggered make a building like new or change of occupancy, were one of the bigger barriers that we've discovered in working with historic buildings because that's really virtually impossible to make an historic building when renovated be all the same things that would be in a new building. So we're constantly in a judgment call, but the prejudice is there in either expenditure or work. In the historic preservation world, the National Trust assembled a team of experts in 1974 and looked to sort of the what should we be doing with building codes. And there were lines in there that came out of Virginia, but basically the idea that we're working with the building official to make sure the building is safe. And we really ramped up the qualifications that approvals would be based on submissions of professional architectural and engineering plans, and now we're expanding that into reports that documents why something's important and why a treatment might be an alternative to safety. In 1987, the Boca National Code developed a special chapter on existing buildings and a unique performance scoring system, which we're going to talk about in a little more detail later because it's still one of the more innovative tools in the system of building codes and historic preservation. But it wasn't until 2003 with the establishment of the International Existing Building Code that we actually had a national model code for existing buildings that like the other I codes is uniform across the country has the same kind of provisions that people can understand, and it has an historic building chapter. So we built in a lot of the special things about historic buildings into a separate chapter on that. So the IEBC comes out with a new addition each three years. So the 2021 is the current addition. But many of your communities kind of lag. It's not uncommon for a community to be using a 10 year old version before they adopt the new one that changes around the country. But at its broadest, what building codes say about historic buildings can be categorized into sort of three larger frameworks. First, it could exempt historic buildings, and that was true in the International Energy Conservation Code up until 2012. It just said, if you're an historic building, you don't have to meet this code. That changed in 2015 moving forward. So know where you are with the energy code. It can have no provisions about historic buildings, and that's a unique situation with the residential code, which I'm going to talk about in more detail. But on the whole, mostly what we're seeing is that within building codes, when there are historic buildings that are affected, there are special provisions, largely called technical alternates. There's a whole chapter about that in the International Existing Building Code, and you'll also find this provisions in the accessibility and energy codes. Now, who adopts codes and how does this happen? Well, basically, depending upon how your state works and how the enabling powers are to local administrations, codes could be adopted at the statewide level and apply to all jurisdictions, or it could be given to local adoption. And also, some states do other codes than the IEBCs. Ohio in particular works with a different code, and California is not worthy for having a separate historic building code. But on the whole, there's an adopting authority that establishes which code you're going to use. Primarily, the ones that mostly affect commercial and institutional historic buildings are these, the International Existing Building Code, the Energy Conservation Code, and the Standards for Accessibility, which we're now using the term universal design as a more broad envelope term for all kinds of abilities that people have that are affected by the built environment and how we can make it better. But I want to take a little more time and talk about the details of the International Residential Code, which applies to single family, two family, and attached townhouses. And the residential code is very different than the other codes. It's meant to be used by the builder, and it's not as complex a document. It's meant to be a standalone document for all aspects of small frame and residential construction. Unfortunately, it has absolutely no provisions related to historic buildings. So when you think about it, historic houses are the greatest number of historic resources in the country. The Uptown Historic District in New Orleans is something like 10,000 buildings. So literally the greatest number in the millions of historic designated properties in the country are residential. And yet we have this odd thing that the residential building code doesn't give any special consideration. This is a large deficiency that we're going to talk about that. But what it does have, and this is an unusual thing, the International Residential Code has an appendix that applies to existing buildings. Unfortunately, when you adopt the International Residential Code at whatever level, state, local, you must separately adopt the amendment for existing buildings. So this appendix isn't even automatic when you adopt the International Residential Code.  It's not specifically geared towards historic buildings, but it says where compliance is technically unfeasible, or where to impose disproportionate costs or dimensional difficulties, the building official can accept alternatives. And some of those alternatives are things that might be outlined in the International Existing Building Code, but this gives you specific language in the code that says to the code official, I'm going to strike building, I want to use some other alternatives because my building is historic, but only applies if it's been adopted when you adopt the International Residential Code. Now, adopting and amending the code is common. Many states adopt codes and then have amendments. Larger cities when they adopt codes might have extensive level of amendments. California has its own state historical building code and an incredibly important reference for any of you working with historic properties. And Ohio uses an older version of the building code that's not an ICC code but goes back to the BOCA codes that has provisions for historic buildings. Now, our APT Codes and Standards Technical Committee has a link on our web page to all of these various local amendments to building codes that are done. And we've got quite a few, but I would emphasize I think that California and Ohio are two of the more important ones for the extent of which they address this. And I'm even going to dig a little deeper on this topic with you. We recently worked with the city of Denver, Colorado, which made extensive amendments to its residential code. They adopted Appendix AJ, and then they added a couple of other really interesting provisions. First, they added provisions about who says a building is historic, who can evaluate the historic preservation features. The building code official largely says, I don't know what's historic or not in a building. So this gives a guidance on who has the qualifications to say my building's historic and this element of the building is historic. And they also added a really comprehensive dimensional tolerances list. One of the irksome things about codes has been if we have a new standard and there's an exact precise dimension for something, and your old building doesn't meet that dimension, then it's not in compliance. But what if it's almost in compliance? Well, the Denver code went through about over 100 different dimensional requirements. Largely said most things if they're historic, you've got an automatic 10% compliance alternative, a discretionary factor. Some items, they said no. If you have a minimum ceiling height, you can't make it any lower than that. But they went up to as high as 17% dimensional on door openings, so that an older door might be a 30 inch door could meet the requirements of a 32 inch door for accessibility purposes. So they really look closely at dimensional tolerances. And it's a unique document of any of the cities we work with that have amended the residential code for historic preservation purposes. There must be something in the water in Colorado because Telluride, Colorado, created one of the most extensive amendments to the appendix of the residential code and even the non-residential buildings, the international existing building code, called historic building enhancements to the IEBC. And it's actually even credited to the National Trust as part of the organization that helped develop this. But this has an extensive list of alternates on code compliance, the dimensional tolerances in there, as well as many of the factors that are in chapter 12 of the international existing building code. So these are two essential resources for you to look at if you're thinking about amending the code for residential purposes in particular. They're all online and they're all referenced to the APT codes and standards technical web page. Now here's what the Telluride code says. And this is the language that's fairly typical now across the universe of historic preservation. When historic building is being repaired or being changed in its occupancy, it shall be investigated and alternative. And then the requirements that are at issue, those things where there's potential conflict should be addressed in a written report filed with the code official by a registered design professional when such report is necessary in the opinion of the code official. So it asks the code official to say, put it in writing, give me your technical alterments, give me your case, so that I can judge that you've reached an alternative and important level of safety with historic features that may not truly come applied to the dimensional or other requirements of the current code. So this idea of a report from the professional is the new status program for how to adjudicate this issue of historic buildings and code compliance. Now, just to step back from this a bit, the International Code Council has a publication for the Building Department Administration. And this quote is worth your knowing because it tells you why it's so hard. The repair, alteration, addition to, and change of occupancy in many existing buildings are in many cases more complicated to design and regulate than the construction of new buildings. This basically says what we've all known. It's really harder to put all the new requirements and apply them uniformly to an existing building because there's going to be things like dimensional discrepancies or fire separation discrepancies that may be minor, but how do we fit that into the code? So the ICC recognizes this is a hard part of the job, and your local code official is the person who has to make these judgment calls. So why is it more complicated? Well, there's more than one code path in the code. The IBC has three that I'm really going to talk about. Most architects and code officials use the path for new buildings. So there's more training and awareness of how to use it on new construction. So they're not as informed. And that's part of our goal as APT is to help develop that training. We recently did a national training on this. The code is not a standalone. It's a reference to other standards. So you've got to go back and find reference points. If you have the IEBC, you've got to have the IBC as its companion. And ultimately, all the code language is subject to the acronym AHA, the authority having jurisdiction, your local code official. Now there is an important historic preservation chapter in the IEBC. I'm going to talk about that in a bit, but it hasn't been updated a lot. And codes also are subject to local amendments. And that can be a promise for us because if we amend the code appropriately, it can help us in our work. So here's a summary chart that actually has a lot of information in it. But I'm really going to bring it back to this idea that the international existing building code is one code with multiple paths to code compliance. And I'm going to cover the three principal code paths. But there are provisions in the code that apply to all buildings. That's in chapter three. And there are some issues that come out of energy codes and fire codes that come into all the compliance methods. But largely there's three principal compliance methods that you're going to look at with historic buildings. The first of these might be the prescriptive method. And this is similar to the code path for new buildings. But interestingly, the language in the prescriptive method says the provisions of this code that require improvements to a building's existing condition shall not be mandatory for historic buildings unless specifically required by this section. And it all gets back to the code official making the relative judgment of safety. So this language shall not be mandatory is useful because it says there's discretion, but it also comes back to the code official needing to make that discretionary judgment on something. And that's why you make it clear. So shall not be mandatory is useful, but it comes with that safety prerogative. The work area method was one of the innovations in the IEBC that's tremendously important and very helpful because this implies applies when you're only say working on a part of a building. So what the work area method does is it's proportional to the amount of owner work that they're going to take on. So if you're just if it's a three-story building and you're only working on a third floor apartment, you might just be doing an alteration level that's minimal one or two. Not extensive to that. And there are lower requirements for what you have to do to proportionality. The one distinction though I will make in the work area method is that if you're going to a change of occupancy, the code is still pretty much works like the old days that it really wants you to make it more like a new building. So once you hit a change of occupancy, it triggers much higher work requirements. The historic buildings generally are part of the work area method. So the special chapter for historic buildings is part of this method. A third method that comes out of the Bokeh work in the 80s is this idea of fire safety scoring. So the performance path is an entirely different approach to evaluating fire safety. It has multiple categories of fire safety in a building.  And based upon that scoring, you can basically achieve a fire safety. And where we found this really useful is it's good on smaller mixed use main street buildings. And it allows the designer to basically select tradeoffs between I will make more fire compartmentalization or more alarms and detection or I'll add sprinklers to the building and various ways give you so many points, extra stairs, all of these things then can be tradeoff. So it gives a lot of flexibility to the designer in figuring out how to make the building the safest it can be while respecting historic preservation features. So we found it to be a pretty effective tool for small, let's say up to three-story mixed use main street buildings. Now chapter 12, the historic preservation chapter, basically has kind of an odd language in it that it says every historic building that doesn't conform to the construction requirements of the code and constitutes a distinct fire hazard shall be provided with a sprinkler system. But then it gives an exception immediately where it says where the code official approves an alternative life safety system, which could be coming from that chapter 13 performance method or some other technical alternatives. One of the irksome things we found in this is that the term distinctive fire hazard is supposedly defined herein in the code, but the code actually doesn't define it. And we actually, and APT proposed a definition of what would be a distinct fire hazard. And this comes from the California historical building code and we actually propose this to the International Code Council. It's working its way through their system. It hasn't been integrated into their system yet. And we don't know at what time it will be. But the point I'm making is that there's some language for historic buildings that sometimes is very helpful and sometimes there are things like this that says it's a distinct hazard. You must address it, but it's not clear what is a distinct hazard. The IEBC chapter on historic buildings gives you a lot of guidance on technical alternatives for these main categories. And I'm not going to go into all the details of this in today's presentation, but there are specific little things that are really good in this because it tells you, you do this, you're equivalent to that. So these are good technical alternates for little components of the building that work through the chapter 12. Another aspect of historic buildings that's really important in the historic building chapter is it has special provisions for historic house museums, what we might call interpreted historic buildings. If they're under 3,000 square feet, basically it allows you to do a lot of things with guidance and tour guides rather than physical changes to the building. So it assumes that it's not an occupied building. No one is sleeping in it. So these interpreted historic structures are actually quite safe because they're not being occupied full time and there's always a guide or a staff person taking people through them. So they're given a lot of exemptions and they depend upon the occupancy management approach rather than prescriptive fire safety things. A couple of examples of historic houses here and for me I'm in Illinois, but the Lincoln home is one of America's oldest historic house museums and at the modern end of the equation, Bucky Fuller's home in Carbondale, Illinois is one of the more recent historic house museums in our state and reflects the great variety of buildings that come under this unique aspect of interpreted historic structures. Now I'm going to touch on a technical detail of the code compliance, which I think is one that gets to about this issue of what's a distinct hazard and how the code can be very generous at times. For historic buildings, grand stairways shall be accepted without complying with handrail and guard requirements. So existing handrails and guards and stairways shall be permitted to remain provided they're not structurally dangerous. So the code pretty much says if you got an old building in the stairs, your historic handrails and guardrails are okay. But what if you don't have a guardrail or a handrail that goes all the way through? Or what if you have a very low guard rail height? The code basically doesn't really talk about this low guard rail height.  But the example on the right, they added something on the top because it was a low height. And this is a good example of discretionary additions to make buildings safer and meet modern requirements. On the left, a modern compliance handrail is added on the side of the stairs where the stairwell did not go all the way through. So this is much safer. And I think these kind of changes are discreet. They're small scale. They don't damage threaten or destroy the historic character of building. So there's a lot of little safety aspects like this that are fairly easy to add to buildings and don't really threaten. They might have a small visual character effect, but don't really destroy the overall sense of a building. Handrails in particular, the modern requirement for handrails is a very small dimension, a circular round shape that's easy to grab a hold of, that's continuous, that extends beyond the stairs. Virtually no historic houses or historic buildings up through the modern era had that. But older handrails were grabbable. They had curved surfaces. They had shapes. So basically the code grandfathered in all these old handrails. And if you've got them, that's largely grandfathered. And I don't think it constitutes a distinct hazard. I think the issue for me is if there's nothing to grab a hold of, it's too wide or there's no handrail, that's when we have a distinct hazard. But probably the biggest conflict we've seen still within the historic preservation world is when there's a change of occupancy. So you don't get many breaks as an historic building when you do change of occupancy. This triggers the highest degree of required changes for egress, fire protection and separation, alarms detection, or possibly sprinkler systems. And what the performance system does is it helps you adjudicate those values, the egress versus protection versus sprinklers. So that's a good technique for getting to this. But when you change the occupancy, the code still pretty much require a much more thorough evaluation of safety. Last I want to touch on the energy conservation code. Historic buildings were exempt from the IECC prior to 2015. Starting with that edition, or starting with the 2018 edition, the requirement that you have to do something to historic buildings was added. And here's what it says. If you have an historic building, the provisions of the code are not mandatory, provided you do a report with the code official or design professional, or even in this case the SHFO or historic preservation authority, demonstrating that compliance with threatened to greater destroy the historic form, fabric, or function of the building. So this is kind of where we're at today. A report signed by someone with authority say, I don't want to do that. I don't want to rip out my historic window and put in a new window. I want to save it and use it and add a storm window. The energy conservation code says that's an action. You could have that. But actually, the energy conservation code is more liberal than you might think. Because the energy conservation code actually permits repairs to existing features. So it doesn't say you have to remove your window and make it new. It says you can retain existing features like windows. You can add storm windows. What the energy code says is you have to make everything better in terms of its energy performance. But it doesn't absolutely mandate uniformly everything to do that. It does prohibit actions that make a building worse. For instance, if you take the plaster off of a brick wall and that's an outside wall, that wall now doesn't perform as well for energy efficiency. The energy code says you still need to do something to achieve an equivalent level of barrier to energy transfer that you had before. However, like the other codes, the change of occupancy provision in the energy code triggers higher efficiency more broadly through a building. So we still see this change of occupancy trigger for more intensive actions. Now, if you are an historic property owner, you're an historic preservation commission, you're staff with a CLG, if you want to know a lot more about how historic codes work and what some of the issues are with them, our APT codes website has a lot of resources for you. We've put together a directory of building codes in historic preservation, research reports, state and local amendments like the ones in California or Telluride. We're putting all the legacy codes online and we're also proposing changes to the international existing building code and we're posting what we're proposing. None of those proposals have gone through yet, but we're working as a committee at the ICC level to change the building codes and make them more efficient for historic preservation. Another parallel part of the APT action is our Building Technology Heritage Library. This is a free online resource of all kinds of older trade catalogs, builders guides, house plan books that help you look at what our ancestors said about buildings and how they're made, and we have now started a program to put all the older building codes on there. If you're looking at legacy building codes, this is the place where APT is providing that resource. APT through our work is really trying to develop comprehensive ways to see how historic preservation and building codes work with each other and can make buildings safer so they have longer lives into the future. Thank you. Thank you, Mike. We're going to switch gears now and we're going to talk about housing and we're going to talk about property protections. We now know about the process of working with the codes for a rehabilitation project of any sort, and now we're going to back up and talk about minimum standards when there is no possibly rehabilitation project that's planned. We'll go way back. We'll go back to the 1930s and the Depression and the New Deal when thousands and thousands of people were unemployed and were unable to pay their mortgages and were homeless. The federal government stepped in through the Homeowners Loan Corporation as the attempt to stabilize real estate, refinance mortgage, they assumed debt, and developed a comprehensive U.S. housing plan. Unfortunately, as we now know, as much of this was done through the redlining process where the maps were drawn of different cities where the federal government was going to assume mortgages and to identify those areas that were risky or safe mortgages. This is the origins of the redlining process. Through the 1930s and up to World War II, quite a number of different steps and efforts and agencies engaged in mortgage stability and home ownership and public housing. These are only some of the examples of the legislation that was passed to try to deal with the housing shortages at that time and the housing needs of the country. In the 1950s and the 1960s, we saw major programs through the federal government and state government supporting public housing. You can see in the top left photographs the kinds of neighborhoods that existed before these programs came and demolished those buildings and those neighborhoods in order to build these large blocks. It wasn't very long before it was figured out that this wasn't really a great solution for large families that multi-story buildings and single elevators and rather unsavory conditions were not appropriate or not productive. You can see, oddly enough, on the right side the 1980s rehab of this very public housing of this very project that's shown on the left. The most famous of these and the failure were the Pruitt Homes and Igo Apartments in St. Louis which were constructed in the 1950s through those best efforts of the federal government and within 20 years were demolished. They were racially segregated. It was a middle-class complex 11-story towers and a lot has been written about the failure of this and similar similar programs. Now, oddly enough, we get to soon start talking about the interstate highway system really known as the National Interstate and Defense Highways Act 1956 and yes, it connected us as a nation but in addition it was part of the support for the growing suburbs and the types of highways that were built helped people leave the city. Not those who could afford to leave the city. Not those who didn't have those resources. The map on the right shows you again some of those red-lined areas of 1937 meaning that those were immigrant communities those were lower income communities. On the left side there's a neighborhood from 1963-1965 that little photograph shows that neighborhood demolished and the highway going in and again there's the overlay on the right side showing us the highway system the red lines area and the areas that were so much demolition occurred. In 1965 President Johnson dealing with the condition of the cities and a lot of racial strife throughout the country called for the creation of a commission to study building codes, housing codes deal with the slums, deal with urban growth, sprawl, blight and to ensure decent and durable housing for the citizens. The number of commissions and reports the current commission probably most important to us is the Douglas commission as published in 1969 and it said it like it was anger of the disinherited city slums as prisons the critical problems of segregation restrictive zoning and it called for political commitment and to increase the power of city governments to deal with these conditions spoke to substandard and unaffordable housing adequate housing availability inconsistent building codes the lack of minimum housing codes and said we need bold solutions to address the enormity of our urban problems. Quite a number of studies that addressed minimum standards and acts that were passed it was 1965 when HUD was established and their minimum property standards first published there's been many iterations of that these minimum property standards are for projects that have some sort of federal assistance for housing so whether it was section 8 whether it was through the mortgaging for the construction these were HUD's minimum property standards trying to deal with creating minimum minimum standards of decency in these structures. There's an overlay to public health you'll hear a little bit more of this or return a little bit more of this from Mike some of the codes the back and forth between housing and public health the tenement housing laws in New York City now housing laws and finally the public health association dealing with hygiene. It's important to note that housing codes and property maintenance codes and minimum property standards are not the same as building codes or construction codes or as we said we were interested in the existing building rehab code those housing and property maintenance codes are dealing with very very basic standards for conditions of typically rental properties. Is there heat is there plumbing is the electrical safe what about the carbon monoxide is the building structurally sound is there lead is there mold what about pests is there blight is there water entering the building so many cities have their own housing codes and it would deal with these kind of very minimum standards as compared to the building codes the construction codes or the existing building rehab codes which dealt with the minimum standards for construction for new or in the case of the IEBC existing buildings it's very easy to think to confuse these because they're often both enacted at the local and or the state level and may even be within a single department within the locality this is what the property maintenance codes want to deal with these existing buildings unoccupied sometimes these are occupied it's a function of code enforcement this is one of the international codes for property maintenance very very very important code that has not yet been given its due so when code enforcement deals with properties they say hmm is is are the lawns mode is the trash taken care of very mid it starts with very minimum observations of the condition of say an outdoor stoop or windows or items such as this maybe next the building has deteriorated a little further still salvageable and we receive some sort of a notification that the building is posted that it's not to be occupied and for many buildings unfortunately it's not really too far along until this happens we lose the building and all of the opportunities that that building presents to its community so what happens when those buildings are demolished particularly where you've got row houses or buildings that are adjacent to each other well on the left we have a building that always relied on the adjacent building to be a moderating factor in terms of the external environment winter snow water ice and what do we have now some insulation that was put up that already is deteriorating of equal concern on the right is buildings where the what were party walls or shared walls were constructed with a lesser quality brick not intended for exterior exposure and all of a sudden that wall is exposed and that building becomes structurally very very vulnerable this one's particularly vulnerable adjacent building is demolished you can see the quality of the brick somebody parched it maybe the municipality did that once they did the demolition but it's not holding up and then that building becomes at risk and then what happens we may lose a whole whole neighborhood so there's no context at all for what was there before we lost all of that opportunity to reuse these buildings and maintain the maintain a community not even just the historic integrity but just to have a community here these are some recent statistics to that I've seen to talk about demolition and I show this because when a municipality takes on demolition or in these cases an emergency demolition the costs can go as you see just a simple small garage $6,000 good size building $365,000 but the average range is right in there in the $50,000 and oh my gosh what kind of protection a little bit of electrical upgrade patching a roof something that would let that family stay in that building what are we missing that we will can't spend the money in our community to take care of these structures and use them for housing but we can demolish them some of you are from communities where you've seen this before the famous red X and all been in New York we've we see quite a bit of these and it posts a building a vacant building that is dangerous for emergency responders and tells them to not go into that structure in the case of any kind of an emergency comes from the fire code some of the requirements of the fire code are retroactive not all of the fire code is retroactive it often is by fire service in your community so we may find there's a little bit of disconnect between the building department and the fire department we're both using the same code sometimes or the same family of codes but most interesting to me in the context of this talk are is section 311 the placards of the fire code which says that any vacant or abandoned building it's determined to be unsafe structural or interior has those marked and that marking is applied on the front of the structure is a 24 by 24 red background white reflective stripes and white reflective border or the purposes of directing the emergency personnel to not enter the building these are often vacant buildings sometimes they've never been in the building there's an unsafe stoop at the exterior there's some other issue in the building but it appears unsafe and they've been directed to go and find these buildings and to mark them it's kind of the depth now for those structures so it's one thing to have a single building but what does that do to the adjacent properties who wants to invest in those adjacent in this case beautiful 19th century buildings where you've got a vacant structure that someone has said is unsafe what happens when there's multiple structures again you can just see the contagious the contagiousness of this and the devastating effects on a community this is a recent article from the New York Times about the housing supply what it says is we have a major housing supply through the US a housing shortage we don't have enough housing and it's not just within the major cities it's all over the country we know that by cost we know that there's just insufficient numbers of housing available and there's articles here's one from the American Planning Association again just from last year how adaptive reuse can help solve the housing crisis well it's one thing for it to be in California and the transformation of a 1960s building for affordable apartments for artists here's another more recent article why we need to save existing buildings why it matters more than anything this is in the context of climate change and embodied carbon but let's go back to that 1960s building why not these structures why are we happy to create affordable housing for artists and to dedicate our resources there but we have not developed a program yet sufficient to save all these other opportunities these are opportunities to address our housing crisis in hiding in plain sight so I'm going to conclude this session talking about advocacy advocacy that all of us can get engaged whether we're architects or engineers or members of local commissions or just others interested in protecting these well these codes matter because when we're talking about construction and rehabilitation we need codes that encourage rehabilitation and that is the existing building code it's not trying to make these buildings meet the standards written for new construction these codes are predictable they contain appropriate solutions and they should be adopted in your community as one tool to encourage rehabilitation it needs work it can be improved and we're continuing to do that but it's trying to balance competing but really many complementary issues preservation, historic integrity address energy, address safety address accessibility but the slides that I've just shown also talked about basic maintenance basic property protection and we need these too we need to encourage the protection of those buildings every one of those opportunities through sweat equity individual property owners can take on a project we the start preservation community needs to be engaged in how those buildings are treated are they identified and are there programs within our community that can help protect these buildings and make them available we need to encourage the commitment of the locality of code enforcement and make sure they've got staffing and resources and enforce legal procedures to protect these vulnerable buildings and their vulnerable occupants we the start preservation community but we have the buildings we know where they are a little hole in the roof as you see on the right should not be sufficient for letting this building become so deteriorated that nothing is possible except a demolition we have the track record we have hundreds of thousands of main street buildings that are all opportunities and we also can demonstrate that we have hundreds of thousands of housing units that have been created using the federal tax credits what we need are programs to work with those most vulnerable buildings to protect them so that they're available for that sort of continued use and reuse we need vacant building programs where the vacant buildings are registered and they're monitored we need partnerships for others who are dealing with economic development building vacancy the center for community progress has some fantastic programs we need vision we need commitment we need creativity just some different examples that I've identified where existing buildings have become to be understood in different community as opportunities that can help with housing shortages so what can all of us do well local commissions and staff I know you're not experts I work with many of you all the time and typically you're dealing with exterior buildings and at best if you're a certified local government you get to reference the secretary of the interior standards you see a lot of projects with replacement windows and siting and stoopes and railings you see a lot of requests for demolition construction but increasingly you're seeing different kind of projects you're seeing exterior continuous insulation on siding you're seeing continuous insulation above the roof which has roofs which have impacts on cornices and other exterior elements you're dealing with mid 20th century buildings storefronts and facade cladding you're dealing with solar on the roofs and you may be dealing with some of these red X's and these emergency demolitions but you also need to know that there are alternative codes and code paths for existing and stored buildings and to be the advocate for those to be adopted in your communities you need to strengthen your relationship with the building of fire officials and we need to all address vulnerable properties and those vulnerable residents commissions and staff and the architects engineers and code officials have to continue to learn about these various code options you too, we too can make sure the IEBC is adopted we need to start engaging as a team to work with the code officials not see ourselves at opposite sides of the table and with with all selfishness I hope that some of you will join our code development efforts to make these codes better and that of course us is the Association for Preservation Technology we may have to change or revisit our messaging or historic preservation messaging why do we save buildings climate change, carbon reduction save on landfill and demolition costs capitalize on the embodied energy that was used for original construction we can reuse existing infrastructure, we've got water we've got septic, we don't have to go through extensive extensive planning reviews we can create walkable neighborhoods we can help individuals build wealth, we can create housing it's good for economic development it's good for jobs, it's good for the tax base and of course most important it's our obligation to the future what about code enforcement well let's change the name let's call it code engagement we all engage in this we have to collaborate we have to support municipal efforts deal with vacant building registries land banks, support the legal processes as I said before make sure that the code offices have adequate staffing and resources and we want to encourage programs that let individuals rehabilitate existing single structures we need the proper tools for that you need to have the existing building code or some version of it and the property maintenance code enforced and active in your community what's the best way to save buildings hands down early on and what's the safest structure in your community it's the rehabilitated building so thank you very much I hope that you will contact me and Mike and he gave you quite a bit of information about finding us on our APT website there's a lot of information there and we are very interested in working with communities who want to look at these model codes and craft them so that they can be strong preservation tools in your community


Oh my goodness. Yeah, I got it set up with the creamy tree. It's about to be a banger So um pristine auction so pristine auction did the last NFL mystery box video I did it was five thousand dollars worth of stuff and that video is awesome We loved it so they hit me back up and they're like hey, that was a banger. Let's outpace it Let's do a ten thousand dollar NFL mystery box opening and that's exactly what we're doing today Hey boys, so quick overview of pristine auction if you missed the first video we did I like to think of it as eBay, but for all the best sports stuff in the world They've got daily auctions that go for 24 hours Everything starts at a dollar and there's no reserves Thousands of items are put up every single day an incredible place to get gifts for anyone that you know Who's die-hard sports fan as you will definitely see in this video They've got some crazy stuff on there all autographed items are guaranteed authentic a and use my registration code MMG You'll get ten dollars off your first invoice check the links in the description to check it out. Enjoy this banger I have like oh, I can't I can't turn it right now because you're dueling. I'm getting you're gonna be in this Though don't put your shade dad. I have a camera woman for today, which is awesome.  All right, so for now, I'm gonna get straight into this opening.  Show me it. Show me your wiener. Thank you Hi, baby paints.   It's gonna be a banger Oh, it's gonna be first. He's so we got so much line stuff last time I'm gonna be honest I don't know what I'm gonna be able to do with all this stuff because a lot of stuff from last video went into my set But I don't know my sets already pretty packed you black sand is taking up a lot of room So I don't know oh, okay. We got a replica helmet to start us out I'm gonna see if I can guess what it is based on the color. Oh, it's it's it's lions.  It's one of the matte black lions home So holiday Stafford Barry Sanders Megatron The Andres Swift signed matte black lines. Oh, that's a good way to start box within a box Well boxception is next. I love I love this much box I'm seeing Aaron Donald. What do we got here? Yo, so it's like an og Rams helmet black and white But it's got Aaron Donald signature. You're like look at that.  I Love it. All right. We got another helmet here. This is Colts. Who the hell could I have that's Colts? I'm assuming this is Peyton Manning. It's gotta be Peyton Manning or is this Pat McAfee? It's Peyton. I thought it could be Maggie was like we got a Peyton Manning signed helmet up next I literally feel like a kid on Christmas right now. This is so awesome Peyton Manning and Peyton Manning is the one kind of believed to me for the golf thing He said my swing was decent didn't say that much great stuff, but he didn't pull a Charles Barkley Peyton Manning signed helmet That's the prettiest one. Yeah, that's prettier than the swift and the ear doll. Oh Mmm, I smell Texans who could be Texans J.J. Watt the Sean Watson. Oh I got a mix up if you guessed Will Fuller you were correct. How many signed helmets they have at their warehouse is just baffling to me Will Fuller got lots of helmets. This is the helmet box right here We got a will Fuller signed helmet at that crispy white thing.  I'm gonna recycle it all don't worry guys. I mean California I'd get burned at the stake if I didn't so This is the helmet box. Yeah, definitely the helmet box I'll let you guys look at this one first and take your guesses. I think I saw Cardinals I mean, there's a lot of there's a lot of good options Larry Fitz Kyler Murray. Oh, no way This is a Murray. Come on.  You gotta love that one man the final helmet I'm looking at is an eagle. Who is the Eagles player in here? Eagle is struggling to say it could be like a vintage You can be an old-school Eagles player. I was totally right, bro Who who are you guessing vintage old-school Eagles player absolute stud if I said weapon X would that help you?  It smells like brand new. Oh my god. I love it.  Actually? That's awesome. Yeah, this thing is tall because I'm six foot five This is like this is like a five and a half foot tall box right here. That's I'm guessing it's like a signed Jersey. That's already framed or something. What am I looking at, bro?    I can't imagine there's more helmets, although I totally be wrong You can just have an army of helmets. Oh, yep. It ain't a helmet box I definitely just saw Jersey and it looks like a Seahawks player. I would be lit if this is DK Metcalf But Russell Wilson's gonna let's be connected.  Oh my god, numero uno signed DK Metcalf Jersey He's no Megatron, but he could get there. Let me in let me in your box. Let's go look at that Dude, this is like a size that could almost fit me to DK Metcalf Signed on the back dude. They were not kidding when they said 10k because oh my where do I start? Who do we got? Oh? Chad Ocho Cinco is number two dude and honestly for some of these like I know I'm not gonna wear I love Ocho Cinco, but I'm not gonna wear an Ocho Cinco Jersey And I think this one would be for a giveaway So I'm gonna keep this in the packaging in case I send it off to one of you guys so that you know This is the verified signed Ocho Cinco Jersey that is gorgeous Looking at something red. I'm thinking chiefs It's not this this one is George Kittle fire George kiddles up next You see like like that's not a good signature Like this man is one of the best if not the best hide-and-the-league and he's signing that like he's in he's 14 years old Come on bro when I was looking at the helmets before I said the Andre Hopkins and we got the Andre Hopkins Cardinals DHOP What do we think? What are we rating that signature? I see the D and I see the H But yeah, this one totally a giveaway one too. So I'm keeping this boy in the plastic Lions lions lions lions lions lions is it lions? Oh, no, we're looking at is this Giants Oh, push your prayers up and hope this man heals signed Saquon Barclay Jersey, dude. I feel so bad. I wanted to watch this dude play plus that line That Giants team is just abysmal so he would have just pulled them from the ashes heal up my guy He'll okay now we got some stuff. That's totally different looking a little ladenian Tomlinson Mini signed helmet last time we got a tire to kill one this time. We're looking at LT Yeah, I got hit my boy pick up. I think I could sauce this his way. Oh, it's Matt black to Hall of Fame Oh, you wrote Hall of Fame 2017 on there, too. That's tough. Oh pylon times, too, baby I'm gonna have two pylons in there. I can make a whole NFL field out of the pylons I'm gonna have it's gonna be signed Let me see if I can figure out who it is just based off the signature because I didn't read who it Was yet.  I was just saying it's a bunch of Jays So like I was good. I was trying to think of a player with bunch of Jays in his name I couldn't think but juju juju Smith Schuster. That's so obviously juju I don't actually know how I gift that this says Geordie Nelson on it. Is this another pylon though? It's like a pile. Oh, wait. It's one of the trophies, dude It's one of those trophies that we got from primetime last time Super Bowl. Oh boy XLV is up 40 I don't actually know Geordie Nelson. This is a Super Bowl champion trophy. It's signed, too I don't understand how these work, but they're so cool. Oh my god. It's like giving birth. I know all about that, right? This is still covered in the embryo same thing with you Jerry Rice gold signature This is oh boy. This is when he was Super Bowl champion in Super Bowl MVP Again, I don't know how these work, but they're so cool still don't know what this could be But there is truly only one way to find out. It's me like a signed picture That's the best thing you've gotten. I'm not even kidding. That's the best thing What? Where did they get this from? This is a signed Carol Baskin.  All right. Well, that's uh, I wish I could make that the thumbnail right there It would kind of throw off the vibe of the video, but that's pretty cool right there. Yeah, I love you Prasheen auction Yeah, this is yeah, I don't know what could be included in this. This could be another like smaller signed poster All right box numero quattro No way you guys guessed this dude that would look so crispy on the wall We're looking at a signed John L. Way that is an og one This would be like a Christmas present for your father aka me There's no way any of you guessed John L. Way.  There's no way you guessed John Final one boys. Let's get naked. Okay. I see a blue border.   Oh god. I'm gonna have to change the whole studio now. I really am. All right, let's slowly Oh, that is so sick. Okay, so obviously it's Stafford. These are like these are like the old like powdery blue jersey So this is a young Stafford right here sign right here. Obviously. It's got the photos on and the like Prasheen auction.  I love you. You really outdid yourselves on this one I don't know if we're gonna be able to top this video. That's kind of an issue. I'm thinking of now Oh my god, look at that. I don't know which one is like I love Barry Sanders more But this is pretty gotta say he's definitely gonna replace the little mini signed Stafford juicy I might well say that much. Wow. I have some work to do on the studio now That's for sure.   Thank you for doing great job filming


All right. Thanks for the introduction. So I'm excited to tell you more about data independent memory hard functions. So let me start off with a motivation, which is really why I started working on memory hard functions. So password storage. We have an attacker that breaks into an authentication server, steals a hash of a user's password. And now the attacker can try as many guesses as they want offline to crack the user's password. They're really only limited by the resources that they invest in this attack. Unfortunately, these attacks are an increasingly common problem. At this point, breaches happen so fast that I'm not even able to keep this slide up to date. And we've had billions of user accounts that have been affected. So the goal of a memory hard function, intuitively, we want a moderately expensive hash function, which should be fast to evaluate on a personal computer, and expensive to evaluate even if the attacker is using some application specific integrated circuit. So maybe some supercomputer as shown on the left here. So intuitively, memory hard function is a function where computation costs should be dominated by memory cost. So our goal here is we want to force the attacker to lock up large amounts of memory for the entire duration of computation. And this intuitively implies that the computation will be expensive even if the adversary is using customized hardware. So we have a couple examples of memory hard functions. Scrypt is a prime example. Here, Scrypt is an example of a data-dependent memory hard function. So the memory access pattern here depends on the user's input. And so we have to worry about side-channel leakage. So a side-channel might leak information about the user's input, which in this case might be a sensitive password. So in this talk, we're going to focus entirely on something called data-independent memory hard functions. These are just memory hard functions whose memory access pattern does not leak any information about the user's input. So to specify a data-independent memory hard function, we need to do two things. We need to specify a directed acyclic graph g and a labeling function h. Now, typically h we think of as being a random oracle. As we saw in the last talk, it's OK for h to be ideal permutation or an ideal cipher. So there's other ways to build h here, but in this talk we'll focus on random oracles. Intuitively, the DAG encodes data dependencies. So the label of an internal node is the hash of the labels of its parents. And the output of this function is just the label of the last node in this graph. So we'll use big n to denote the total number of graphs. And typically, we'll assume that, at least in this talk, we'll assume that n is a power of 2. So we'll use little n for that power. OK, so when we talk about evaluating a memory hard function, a common way to describe evaluation strategies is in terms of graph pebbling. So here we've got a graph. We start off with no pebbles in the graph. Then we can place a pebble on the source. Now that we have a pebble on node 1, we can place a pebble on node 2. Now we can place a pebble on node 3. Now we have the data to pebble node 4, pebble node 5, et cetera. So the rules of a pebbling is basically you have to wait to pebble a node until all the dependent data labels are already in memory. All right, so when we talk about evaluation, we're typically going to use the language of graph pebbling. All right, so now the important question is, how do we measure the cost of a pebbling? And there's a couple different approaches. One nice initial attempt is space-time complexity. So here you just look at the maximum number of pebbles on the graph at any point in time in the pebbling, multiplied by the total time. So this is maximum space used, multiplied by time. So what's the problem with this? Well, the problem is that space-time complexity doesn't amortize nicely. So as we can see on this slide, let's suppose that we have a computation that requires a lot of space initially and then runs for a lot of time without much space at all. In this case, if the attacker wants to compute multiple instances of this function, they can compute all of those instances at one time, interleave them. And here the space-time complexity of computing multiple instances is roughly the same space-time complexity of computing just one instance of the function. So if this is a password attacker, we don't want to give the attacker this advantage. So Alwin and Sermonenko proposed a different metric called cumulative memory complexity or cumulative pebbling complexity for graphs. Here we're just going to sum over all pebbling rounds, total number of pebbles on the graph at that point in time. So instead of the area around this curve, we're going to look at the area under the curve. The nice thing about this is that it actually approximates amortized area-time complexity quite nicely. The cumulative memory complexity of computing two instances of this function is two times the complexity of computing one instance of the function. So we're going to use this notion of attack quality when we evaluate memory hard functions. So the naive sequential pebbling is just going to cost n squared over 2, roughly, pebble node 1, pebble node 2. Keep all the pebbles on the graph. At the end of the day, your cost is roughly n squared over 2. So intuitively, we want to ensure that the optimal pebbling that the attacker might try is nearly as expensive as this naive pebbling strategy. So the attack quality really measures the attacker's success in reducing his cost. So we can talk about the quality of a pebbling attack as the ratio n squared over 2 divided by the cumulative cost of the pebbling. So for example, if we have a pebbling with attack quality 10, this means that the attacker reduced his cost by one order of magnitude. All right, one more metric to measure the quality of a memory hard function, sustained space complexity. So here, this is actually a more stringent requirement than cumulative memory complexity. So we'll define S sustained space complexity as the time or number of pebbling rounds in which the attacker has at least S pebbles on the graph. So intuitively, if we have S sustained space complexity t, then the cumulative memory complexity has to be at least S times t. So this is a stronger requirement. And intuitively, if we have high ST sustained space complexity, then we can rule out attacks in which the attacker has low memory usage for any point in time. What I'll say about this is that building a graph with high sustained space complexity is a very challenging goal. So we gave a theoretical construction at EuroCrypt last year, but there are no known practical constructions with strong sustained space complexity guarantees. OK, good. So let me give you a brief overview of what we know about constructing and attacking depth-for-bust graphs. In particular, there's a property called depth-for-bustness, which is really the key to analyzing data independent memory hard functions. So depth-for-bustness, given a DAG G, we say that it's ED depth-for-bust if for all sets of E nodes, deleting those nodes from the graph still leaves a path of length at least D. So we can say that a graph is ED depth-for-bust if it satisfies this property. If it doesn't satisfy this property, we can say that the graph is ED-reducible. So here's an example of an ED-reducible graph. If we delete these two nodes, then the longest remaining path in the graph is two. So crypto 2016, we gave an attack which shows that if your graph is not depth-for-bust, then we can get parallel pebbling attack that has cumulative memory complexity little o of n squared. So in other words, the attack quality is going to be omega of 1. A corollary here is actually any directed acyclic graph with n degree 2 has cumulative memory complexity at most n squared log log n over log n. So there's this general upper bound. And this actually separates data independent memory hard functions from data dependent memory hard functions. So data dependent memory hard functions, we can get all the way up to n squared, but that's not possible for data independent memory hard functions. And in fact, for practical instantiations of memory hard functions like argon2i, we can get even higher quality attacks. So what about building a secure memory hard function? Well, there's this generic lower bound that says that if your graph is ED depth-for-bust, then your cumulative pebbling cost is at least e times d. And at CCS in 2017, we gave a practical construction of a graph that's ED depth-for-bust, where e is n over log n, d is omega n. Here, this means that CC is at least n squared over log n. OK, so this is nice. Theoretically, this is nearly optimal. And so if we compare to argon2i, asymptotically, dr sample is superior. So then, of course, we can ask the important question. Well, sometimes theory is different from practice. So what about the constant factors here? And in the CCS paper, our empirical analysis suggested that theory matched practice. So here, we can see the best pebbling attack we found against dr sample, and it has low quality. And then we can look at the best attack we found against argon2i, and it has higher quality. So empirically, the theory seemed to match practice. So now I can tell you about our contributions. So we present a new analysis of the greedy pebbling attack, and we show that it's surprisingly effective against dr sample. And in fact, it reverses prior conclusions. So actually, argon2i now provides stronger resistance to known pebbling attacks than dr sample, at least for practical parameter regimes.  Unfortunately, for lack of time, I'm not going to be able to describe that. But you can see the paper for details. I'll just remark that it significantly improves on prior algorithms in all of our empirical analysis. And it potentially has implications for many other cryptographic objects where depth robust graphs are used, such as proofs of replication, proofs of space, obviously memory hard functions, et cetera. OK, another contribution here, and this is a trivial observation, but nevertheless one I include because I think it's important. So there's an easy way to parallelize computation of the argon2i round function. And if you implement this, it actually increases or it reduces the attacker's cost by nearly an order of magnitude. So what about on the positive side? Well, we give a new construction of a data independent memory hard function by combining dr sample with a graph called a bit reversal graph. And we show that this graph has optimal resistance to all known pebbling attacks. And also, it's the first practical construction with strong sustained space complexity guarantees. I'll say more about that in a bit. So we also give a new pebbling reduction for the XOR labeling rule. I'll say more about that in a bit. But this is the labeling rule that is used in practice. So I should contrast the pebbling reduction with Binny and Stefano's reduction. So we're still assuming that H is a random oracle here. But the way that the random oracle is used in practice uses this XOR labeling rule. The way, well, prior pebbling reductions assumed that the random oracle was used in a much different way. And that can introduce some challenges. We also give a construction of an inherently sequential round function so we can reclaim this order of magnitude cost reduction. So let me start off by telling you about the greedy pebbling attack. And this is actually quite a simple attack. So here, we're going to pebble nodes in topological order. And we're just going to discard a node on pebble v after that pebble is no longer needed. So as soon as we've pebbled the greatest child of node v, we can remove our pebble on node v. So it's a simple sequential pebbling strategy. And Bonet et al showed that the strategy yields attack quality roughly 5 against argon2i. So now the parallel pebbling attacks against argon2i, they actually yield a higher quality attack. So we get omega n to the 0.22. So it's an asymptotic improvement, not a constant factor improvement. And for this reason, in our CCS paper, we actually didn't look at the performance of the greedy pebbling algorithm. And in hindsight, that was a mistake. So what we show in this paper is that the greedy pebbling algorithm is effective against ER sample. Namely, it achieves attack quality log n. And this actually matches the asymptotic lower bound. We prove that CC is at least n squared over log n. So this is tight. What's important here is that we have good constant factors. So now if we redo the plot, including the greedy pebbling strategy, here's argon2i. And here's attack quality versus DR sample. So we have high quality attacks against both. But we have even higher quality attacks against DR sample. And this is, even if we go all the way up to n is equal to 2 to the 24, which I think is on the higher end of what one might consider for parameter settings. OK. Now I'll just advertise here. Our new construction is down at the bottom of this plot. So we do find a way to fix the problem. OK. So now we have an attack, which is surprisingly effective against DR sample. We'd like to construct a new DAG, which provides strong resistance to both attacks. So the parallel depth reducing attacks from crypto 2016 were especially effective against argon2i and many other IMHF candidates. DR sample was specifically designed to resist these types of attacks. But as we just showed, the greedy pebbling attack is effective against DR sample. So to construct a DAG that resists both attacks, we start off with this bit reversal graph. Here, we can represent each node by a bit sequence. And we have two layers of nodes. And we'll have an edge from, let's look at this node, 0, 1, 1. So if we reverse those bits, that's 1, 1, 0. So we'll add an edge from here to 1, 1, 0. Now, this is an old graph. It was analyzed by Lingrower and Tarjan back in 1982. And they showed that any sequential pebbling has spacetime complexity n squared. In fact, for this reason, this was the basis of the Katana IMHF proposal. So a natural question to ask is what about the cumulative memory complexity of sequential pebblings? And this is a harder result. But if you use the right potential function, you can actually prove that the cumulative memory complexity is still n squared. So not just the spacetime complexity, but the cumulative memory complexity is also n squared. But this is only for sequential pebblings. So unfortunately, the bit reversal graph is not a good candidate when we use it alone. The reason is that all one in Serbanenko back in 2015, they gave a parallel pebbling with spacetime complexity end of the 1.5. So if you allow for parallel pebblings, actually the spacetime complexity is not very high. So to patch this problem, we overlay the bit reversal graph with a depth robust graph, in particular dr sample. So if we start with dr sample, our depth robust graph on the bottom, and our bit reversal graph on the top, all we're going to do is we're going to move dr sample on top of the bit reversal graph. And this gives us our overlaid graph. The first layer now represents the depth robust graph, and we have all the same edges connecting the first and second layer. So empirical analysis demonstrates that this graph is resistant to all known pebbling attacks. So it inherits resistance to depth reducing attacks from dr sample. It inherits resistance to sequential pebblings from the bit reversal graph. And this includes the greedy pebbling attack in any variant of the greedy pebbling attack, because we can show that it resists any sequential pebbling strategy. But more interesting, this combined graph actually yields stronger new properties. So it's the first graph with strong sustained space complexity guarantees. So in particular, we can prove that any parallel pebbling of this graph either has maximal sustained space complexity and overlog n pebbles for n rounds, or the cumulative cost of this pebbling is even larger than n squared. So this graph actually achieves high sustained space complexity. And in fact, if you play with these parameters, you can guarantee that you need s pebbles for t rounds. And you get a steeper penalty if you decrease s here. We can also prove that under plausible conjectures, which see the paper for those conjectures, any parallel pebbling has cumulative cost at least n squared log log n over log n. So we pick up this extra log n factor, and this would be an asymptotically tight result. We can also now turn our attention back to pebbling reductions. So Alwin and Sermonenko previously showed that any algorithm evaluating our memory hard function, the parallel random model, can be described in terms of an equivalent cost pebbling strategy. So the implication now is that to analyze the graph, it's sufficient to understand the pebbling cost of g. But now we're going to open the hood a little bit and ask what's the labeling function that's used. So in Alwin and Sermonenko, they assume that the labeling function used concatenation of labels. So before we apply the hash function, we concatenate all the parent values and then hash them together. Now in practice, something different is done. Namely, we take all the parent labels, we XOR them together, and then we hash. So we'll call this the XOR label rule. And this tends to be what's used in practice, namely because it's much more efficient. So this prior intuition that we can focus on pebbling cost, one might wonder, is this actually still true for IMHFs that use the XOR labeling rule? And actually the answer is not always. So here's a graph where if you use the XOR labeling rule, the function that you define is actually a constant function. And here, the problem is that W and X, they have the same sets of parents, which means that they're going to have the same labels. And now Y is the hash of label W, XOR, label X, which is just the hash of label 0. So in fact, it's pretty easy to compute this function. And the cost is not at all related to the pebbling cost of this graph. So what we can show is that if your graph satisfies this property, which we call the unique parent property, that now the same pebbling reduction can go through. So namely, the cost of pebbling the graph is equal to the cumulative memory complexity of the function. Here we lose a factor of delta, where delta is the maximum indegree of the graph. And we might ask, is this reduction, is this loss of the delta factor necessary? It turns out it is. So if you take the complete graph, delta is n. The cumulative memory complexity is just n, but the cumulative pebbling complexity is n squared. So in this case, loss of delta is actually necessary in the theorem. But I'll remark that in practice, delta is a small constant, and the unique parent property does hold in practice. So this pebbling reduction covers all of the interesting examples that we would see in practice. So we also find a way to improve the round function. I will remark that we implemented our construction. And you can see here, whether we use the old edge structure or our new edge structure, whether we use the old round function or our new inherently sequential round function, the performance is the same. So the optimal thing to do would be to use this dr sample plus bit reversal graph edge structure, use the inherently sequential round function. This is going to maximize the attacker's cost. So I'm running out of time. I'll just throw up a few open questions. I think one of the biggest open questions is really tightening some of these bounds, these concrete bounds, on cc of g. So we have asymptotically, we're almost there, but there's large gaps between the lower bounds and upper bounds in terms of constant factors. All right, so I will close there. Thank you, Jeremiah. We have time for one quick question if someone has something. You had inputs to some of your functions where the inputs were XORed. And so the question arises, does it make sense to compute partial XORs ahead of time? So the question is, when you're doing XORs, can you compute partial XORs ahead of time? And the answer is yes. You can compute partial XORs ahead of time. And this is actually the reason why we lose this factor of delta in our reduction. So this is exactly the challenge. OK, thank you, Jeremiah.


once again. Yes it is Iowa the cornfields of Iowa providing the unforgettable setting for one of the greatest baseball movies of all time a film that continues to resonate with fans and ball players more than three decades after it was released and long last major league baseball at Field of Dreams has finally arrived featuring the Yankees and White Sox in the first ever regular season big league game held in the Hawkeye State. We certainly hope you're having a great night. Welcome to the Grapkins he's bringing Bob Lorenz and Jack Curry with you when you can't get to Dyer's Whipville for the Field of Dreams game Jack you just create your own Field of Dreams and that's what we've done here in our yes studio but it speaks to the uniqueness of this game. I love this idea Bob I love the charm of it the romance of it the nostalgia of it and I have to imagine that major league baseball has dozens of ideas that come across its desk every year as soon as this idea came up this was not just Field of Dreams this turns into fields of gold for major league baseball you intersect as you said one of the best baseball movies ever with an actual game between two teams the White Sox and the Yankees first time Iowans have ever been able to see a game in their state they have minor league baseball there but they don't have major league baseball so I think the fact that they were able to bring this together I think it's bold and I think it's brilliant let's take a look at some of the facts from the movie which came out in 1989 it was released in May of that year based on the book Shulis Joe by WP Kinsella three Academy Award nominations including for best picture best adapted screenplay and best original score Jack I think it's one of those movies that when it comes out and it's the concept and people they don't flock to the theaters because maybe they just think it's a baseball movie but there's so many more layers to it than that it's a baseball movie but there's so much more going on it as you said Bob it's a movie about life it's a movie about fathers and sons it's a movie about pursuing dreams I forced myself I didn't force myself I watched it again a couple of days ago I wanted to make sure I did my research for this show and there are emotions that tug at you throughout that movie and the idea of wanting to connect and everyone calling you crazy because you're tearing down your farm and you're building a baseball field but I love the movie the first time I watched it Bob I loved it again when I watched a couple days ago and of course the big moment comes at the end of the movie the father and son playing catch but really that relates to anybody you might have a special relationship be it your mom be it a dad be it an aunt or uncle that you played catch with and had that special connection with yeah that's the part I think where the emotions catch up with you and you're right I said father and son but I'm glad you mentioned moms I glad you mentioned uncles or a close friend because that is what the Kevin Costner character is seeking at that point he's hunting down that relationship with his father and I heard an interview with Kevin Costner recently where he talked about how sometimes there are things that are left unsaid and sometimes there are things you wish you had said to your loved one at the moment when you had that chance that game of catch at the end of that movie is the connection between that father and son that had been absent throughout the character's life