

 Feature: Digital Certificates & Encryption

Lance Spitzner tells us all about Digital Certificates & Encryption how they work and apply to Internet Commerce.
"On the Internet, information you send from one computer to another passes through numerous systems before it reaches its destination. Normally, the users of these intermediary systems don't monitor the Internet traffic routed through them, but someone who's determined can intercept and eavesdrop on your private conversations or credit card exchanges. Worse still, they might replace your information with their own and send it back on its way. "

 (Submitted by Noel Mon Apr 17, 2000 )

Digital Certificates & Encryption
This is a white paper dedicated to Digital Certificates & Encryption, how they work and apply to Internet Commerce

Lance Spitzner

The Need for Security


Due to the architecture of the Internet and intranets, there will always be ways for unscrupulous people to intercept and replace data in transit. Without security precautions, users can be compromised when sending information over the Internet or an intranet. This has serious implications for Internet Commerce. For Internet Commerce to exist, there has to be a means to secure data sent over the Internet. Without a secure means of communication, commerce cannot exist.

How do I protect my data?

Encryption & Digital Certificates are the solution for Internet Commerce. Used together, they protect your data as it travels over the Internet.

Encryption is the process of using a mathematical algorithm to transform information into a format that can't be read (this format is called cipher text). Decryption is the process of using another algorithm to transform encrypted information back into a readable format (this format is called plain text).

Digital Certificates are your digital passport, an Internet ID. They are verification of you who you are and the integrity of your data.

Combined, encryption and digital certificates protect and secure your data in the following four ways:.

  • Authentication: This is digital verification of who you are, much in the same way your driver's license proves your identity. It is very easy to send spoofed email. I can email anyone in the world pretending I am the President of the United States. Using standard email, there is no way to verify who the sender is, i.e. if it is actually the President. With digital signatures and certificates, you digitally encode verifiable proof of your identity into the email.
  • Integrity: This is the verification that the data you sent has not been altered. When email or other data travels across the Internet, it routes through various gateways (way stations). It is possible for people to capture, alter, then resend the message. Example, your boss emails the company president stating that you should be fired. It is possible for you to intercept that email and change it saying you deserve a $10,000 raise. With digital certificates, your email cannot be altered without the recipient knowing.
  • Encryption: This ensures that your data was unable to be read or utilized by any party while in transit. Your message is encrypted into incomprehensible gibberish before it leaves your computer. It maintains it encrypted (gibberish) state during it's travel through the Internet. It is not de-crypt until the recipient receives it. Because of the public-key cryptography used (discussed later) only the recipient can decipher the received message, no one else can.
  • Token verification: Digital tokens replace your password which can be easily guessed. Tokens offer a more secure way of access to sensitive data. The most common way to secure data or a web site is with passwords. Before anyone access the data, they are prompted with their user login id and password. However, this is easily cracked using various security software (such as Crack 5.0, etc.). Also, passwords can be found with other means, such as social engineering. Passwords are not secure. Token verification is more secure. Your digital certificate is an encrypted file that sits on your hardrive. When you need access to a system, that systems asks you for your digital certificate instead of a password. Your computer would then send the certificate, in encrypted format, through the Internet, authorizing you for access. For this to be compromised, someone would have to copy this file from your computer, AND know your password to de-crypt the file.
How does it all work?


To understand how this all works, we need to start with the basics. Encryption has been around for centuries, Julius Caesar used encrypted notes to communicate with Rome thousands of years ago. This traditional cryptography is based on the sender and receiver of a message knowing and using the same secret key: the sender uses the secret key to encrypt the message, and the receiver uses the same secret key to decrypt the message. For Caesar, the letter A was represented by the letter D, B by the letter E, C by the letter F, etc. The recipient would know about this sequence, or key, and decrypt his message. This method is known as secret-key or symmetric cryptography. Its main problem is getting the sender and receiver to agree on the key without anyone else finding out. Both sides must find some "secure" way to agree or exchange this common key. Because all keys must remain secret, secret-key cryptography often has difficulty providing secure key management, especially in open systems with a large numbers of users, such as the Internet.

21 years ago, a revolution happened in cryptography that changed all this, public-key cryptography. In 1976, Whitfield Diffie and Martin Hellman, introduced this new method of encryption and key management. A public-key cryptosystem is a cryptographic system that uses a pair of unique keys (a public key and a private key). Each individual is assigned a pair of these keys to encrypt and decrypt information. A message encrypted by one of these keys can only be decrypted by the other key in the pair:

  • The public key is available to others for use when encrypting information that will be sent to an individual. For example, people can use a person's public key to encrypt information they want to send to that person. Similarly, people can use the user's public key to decrypt information sent by that person.
  • The private key is accessible only to the individual. The individual can use the private key to decrypt any messages encrypted with the public key. Similarly, the individual can use the private key to encrypt messages, so that the messages can only be decrypted with the corresponding public key.
What does this mean?

Exchanging keys is no longer a security concern. I have my public key and private key. I send my public key to anyone on the Internet. With that public key, they encrypt their email. Since the email was encrypted with my public key, ONLY I can decrypt that email with my private key, no one else can. If I want to encrypt my email to anyone else on the Internet, I need their public key. Each individual involved needs their own public/private key combination.

Now, the big question is, when you initially receive someone's public key for the first time, how do you know it is them? If spoofing someone's identity is so easy, how do you knowingly exchange public keys, how do you TRUST the user is really who he says he is? You use your digital certificate. A digital certificate is a digital document that vouches for the identity and key ownership of an individual, a computer system (or a specific server running on that system), or an organization. For example, a user's certificate verifies that the user owns a particular public key. Certificates are issued by certificate authorities, or CAs. These authorities are responsible for verifying the identity and key ownership of the individual before issuing the certificate, such as Verisign, http://www.verisign.com.

Authentication & Integrity

We now have a secure means of encrypting data, one of the four methods of securing data on the Internet. Two others, authentication and data integrity, are combined in what is called a digital signature. A digital signature works as follows:

  • Authentication: a specific individual sent a message (in other words, no impersonator claiming to be the individual sent the message).
  • Integrity: this particular message was sent by the individual (in other words, no one altered the message before it was received).
When you email someone, your public/private key combination creates the digital signature. It does this using the following format:
  1. The sender uses a message-digest algorithm to generate a shorter version of the message that can be encrypted. This shorter version is called a message digest. Message digests and message-digest algorithms are explained in the next section.
  2. The sender uses their private key to encrypt the message digest.
  3. The sender transmits the message and the encrypted message digest to the recipient.
  4. Upon receiving the message, the recipient decrypts the message digest.
  5. The recipient uses the hash function on the message to generate the message digest.
  6. The recipient compares the decrypted message digest against the newly generated message digest.
    • If the message digests are identical, the recipient knows that the message was indeed sent by the person claiming to be the sender and that the message was not modified during transmission.
    • If the message digests differ, the recipient knows that either the message was sent by someone else claiming to be the sender or that the message was modified or damaged during transmission.
The encrypted message digest serves as a digital signature for the message. The signature verifies the identity of the sender and the contents of the message.

If the message is sent by someone claiming to be the sender, this person does not have access to the sender's private key. The person claiming to be the sender must use a different private key to encrypt the message digest.

Because the recipient uses the sender's public key to decrypt the message digest (and not the actual public key corresponding to the private key used to encrypt the message digest), the decrypted message digest will not match the newly generated message digest.

If the message was modified during transmission, the hash function will generate a different message digest when applied after the transmission.


Tokens represent the fourth security option by replacing passwords. Tokens are simply your digital certificate residing on your hardrive. When a computer prompts you for your password,  your computer sends your certificate over the Internet instead. Your certificate verifies your identity instead of the password. This is a more secure (and easier) means of verification.

How Secure is all This?

Just how secure is encryption. The strength of encryption is measured in bits, or how big the key is. The bigger the key, the stronger the encryption. There are currently 3 commonly used key sizes used commercially, 40, 56, and 128 bit. Originally, the government allowed only 40 bit keys for exportation. However, this proved far to weak for security. In February of 1997, a college student was able to crack 40 bit encrypted data within 4  hours (http://www2.ecst.csuchico.edu/~atman).

Berkeley -- It took UC Berkeley graduate student Ian Goldberg only three and a half hours to crack the most secure level of encryption that the federal government allows U.S. companies to export.

Yesterday (1/28) RSA Data Security Inc. challenged the world to decipher a message encrypted with its RC5 symmetric stream cipher, using a 40-bit key, the longest keysize allowed for export. RSA offered a $1,000 reward, designed to stimulate research and practical experience with the security of today's codes.

Goldberg succeeded a mere 3 1/2 hours after the contest began, which provides very strong evidence that 40-bit ciphers are totally unsuitable for practical security.

In June of 1997, a organized group of people were able to crack 56 bit DES encryption in 140 days. This group shared their resources throughout the Internet utilizing software called DESCHALL (http://www.rsa.com/des). With a possible 72 quadrillion keys to test, this distributed attack would require an incredibly large amount of computing power. And compute the DESCHALL team did, at some points testing almost seven billion keys per second.

In the end, the DESCHALL effort solved the DES challenge after only searching 24.6% of the key space. (about 18 quadrillion keys!) The winning key was determined by Michael Sanders, using a Pentium 90 MHz desktop PC with 16 megs of RAM.

Many believe this security is good enough. By the time your data can be compromised, (3 months) it is of little value because it took so long.  However, to truly ensure the security of your data, most Internet Commerce uses 128 bit encryption. Keep in mind, key strength increases exponentially, making 128 bit encryption thousands of times more difficult to compromise. Because of its strength, the government has prohibited its exportation, it can only be used within the United States. At this time, no one has cracked this encryption. 128 bit encryption is expected to remain secure well past the year 2000.


Utilizing digital certificates and encryption, users can easily and securely communicate on the Internet. This combination of ease of use and security lays the foundation for commerce. As users gain confidence and experience using these tools, Internet Commerce, much like encryption, will grow exponentially.

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