SHA1 is a bit outdated now, as is MD5. We should probably add support for - at least - SHA256. A good option might be `blake2`, which is secure and fast in software. SHA256 isn't exactly slow either and recent CPUs might even already have native instructions: https://en.wikipedia.org/wiki/Intel_SHA_extensions
You probably meant SHA256 here Fixed!
Switch Bazel to a more secure hash by default (SHA256?)
Switch Bazel to a more secure hash by default (SHA256?).
src/main/java/com/google/devtools/build/lib/remote/README.md src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java src/tools/remote_worker/BUILD src/tools/remote_worker/README.md
src/main/java/com/google/devtools/build/lib/remote/README.md src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java src/tools/remote_worker/BUILD src/tools/remote_worker/README.md
src/test/shell/bazel/remote_execution_sandboxing_test.sh src/test/shell/bazel/remote_execution_test.sh
diff --git a/src/main/java/com/google/devtools/build/lib/remote/README.md b/src/main/java/com/google/devtools/build/lib/remote/README.md
index e8487ec8b16db5..398ef89cb632f7 100644
--- a/src/main/java/com/google/devtools/build/lib/remote/README.md
+++ b/src/main/java/com/google/devtools/build/lib/remote/README.md
@@ -26,7 +26,7 @@ For a quick setup, you can use Hazelcast's REST interface. Alternatively you can
 We recommend editing your `~/.bazelrc` to enable remote caching using the HTTP REST protocol. You will need to replace `http://server-address:port/cache` with the correct address for your HTTP REST server:
 
 ```
-startup --host_jvm_args=-Dbazel.DigestFunction=SHA1
+startup --host_jvm_args=-Dbazel.DigestFunction=SHA256
 build --spawn_strategy=remote
 build --remote_rest_cache=REPLACE_THIS:http://server-address:port/cache
 # Bazel currently doesn't support remote caching in combination with workers.
@@ -39,7 +39,7 @@ build --strategy=Closure=remote
 
 #### Customizing The Digest Function
 
-Bazel currently supports the following digest functions with the remote worker: SHA1, SHA256, and MD5. The digest function is passed via the `--host_jvm_args=-Dbazel.DigestFunction=###` startup option. In the example above, SHA1 is used, but you can use any one of SHA1, SHA256, and MD5, provided that your remote execution server supports it and is configured to use the same one. For example, the provided remote worker (`//src/tools/remote_worker`) is configured to use SHA1 by default in the binary build rule. You can customize it there by modifying the `jvm_flags` attribute to use, for example, `"-Dbazel.DigestFunction=SHA256"` instead.
+Bazel currently supports the following digest functions with the remote worker: SHA1, SHA256, and MD5. The digest function is passed via the `--host_jvm_args=-Dbazel.DigestFunction=###` startup option. In the example above, SHA256 is used, but you can use any one of SHA1, SHA256, and MD5, provided that your remote execution server supports it and is configured to use the same one. For example, the provided remote worker (`//src/tools/remote_worker`) is configured to use SHA256 by default in the binary build rule. You can customize it there by modifying the `jvm_flags` attribute to use, for example, `"-Dbazel.DigestFunction=SHA1"` instead.
 
 
 ### Hazelcast with REST interface
@@ -114,7 +114,7 @@ that supports both remote caching and remote execution. As of this writing, ther
 We recommend editing your `~/.bazelrc` to enable remote caching using the gRPC protocol. Use the following build options to use the gRPC CAS endpoint for sharing build artifacts. Change `REPLACE_THIS:address:8080` to the correct server address and port number.
 
 ```
-startup --host_jvm_args=-Dbazel.DigestFunction=SHA1
+startup --host_jvm_args=-Dbazel.DigestFunction=SHA256
 build --spawn_strategy=remote
 build --remote_cache=REPLACE_THIS:address:8080
 # Bazel currently doesn't support remote caching in combination with workers.
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
index 13a7360532a72f..48704b97db8127 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
@@ -76,7 +76,7 @@ public boolean isValidDigest(byte[] digest) {
   static {
     try {
       digestFunction = new HashFunction.Converter().convert(
-          System.getProperty("bazel.DigestFunction", "MD5"));
+          System.getProperty("bazel.DigestFunction", "SHA256"));
     } catch (OptionsParsingException e) {
       throw new IllegalStateException(e);
     }
diff --git a/src/tools/remote_worker/BUILD b/src/tools/remote_worker/BUILD
index ed5351d039ce8e..3190387a393d27 100644
--- a/src/tools/remote_worker/BUILD
+++ b/src/tools/remote_worker/BUILD
@@ -10,7 +10,7 @@ java_binary(
         # Enables REST for Hazelcast server for testing.
         "-Dhazelcast.rest.enabled=true",
         # Set this to the same function that you run Bazel with.
-        "-Dbazel.DigestFunction=SHA1",
+        "-Dbazel.DigestFunction=SHA256",
     ],
     main_class = "com.google.devtools.build.remote.RemoteWorker",
     visibility = ["//visibility:public"],
diff --git a/src/tools/remote_worker/README.md b/src/tools/remote_worker/README.md
index 32c912a0abdd2c..b4c213ce0ec3ea 100644
--- a/src/tools/remote_worker/README.md
+++ b/src/tools/remote_worker/README.md
@@ -13,7 +13,7 @@ The simplest setup is as follows:
 
 - Then you run Bazel pointing to the remote_worker instance.
 
-        bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+        bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
             --spawn_strategy=remote --remote_cache=localhost:8080 \
             --remote_executor=localhost:8080 src/tools/generate_workspace:all
 

diff --git a/src/test/shell/bazel/remote_execution_sandboxing_test.sh b/src/test/shell/bazel/remote_execution_sandboxing_test.sh
index 38c1c2c04fdce4..0b1522381c3f1d 100755
--- a/src/test/shell/bazel/remote_execution_sandboxing_test.sh
+++ b/src/test/shell/bazel/remote_execution_sandboxing_test.sh
@@ -83,7 +83,7 @@ function tear_down() {
 }
 
 function test_genrule() {
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -92,7 +92,7 @@ function test_genrule() {
 }
 
 function test_genrule_can_write_to_path() {
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -103,7 +103,7 @@ function test_genrule_can_write_to_path() {
 }
 
 function test_genrule_cannot_write_to_other_path() {
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
diff --git a/src/test/shell/bazel/remote_execution_test.sh b/src/test/shell/bazel/remote_execution_test.sh
index c81ce2ed528a04..b47fdaa5ef0f8b 100755
--- a/src/test/shell/bazel/remote_execution_test.sh
+++ b/src/test/shell/bazel/remote_execution_test.sh
@@ -83,7 +83,7 @@ EOF
   cp -f bazel-bin/a/test ${TEST_TMPDIR}/test_expected
 
   bazel clean --expunge >& $TEST_log
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -106,7 +106,7 @@ EOF
 #include <iostream>
 int main() { std::cout << "Hello test!" << std::endl; return 0; }
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 test \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 test \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -133,7 +133,7 @@ EOF
   cp -f bazel-bin/a/test ${TEST_TMPDIR}/test_expected
 
   bazel clean --expunge >& $TEST_log
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_cache=localhost:${worker_port} \
       //a:test >& $TEST_log \
@@ -155,7 +155,7 @@ EOF
 #include <iostream>
 int main() { std::cout << "Fail me!" << std::endl; return 1; }
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 test \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 test \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -187,7 +187,7 @@ EOF
   cp -f bazel-genfiles/a/large_blob.txt ${TEST_TMPDIR}/large_blob_expected.txt
 
   bazel clean --expunge >& $TEST_log
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -215,7 +215,7 @@ EOF
   cp -f bazel-bin/a/test ${TEST_TMPDIR}/test_expected
 
   bazel clean --expunge >& $TEST_log
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_rest_cache=http://localhost:${hazelcast_port}/hazelcast/rest/maps/cache \
       //a:test >& $TEST_log \
@@ -245,7 +245,7 @@ import sys
 if __name__ == "__main__":
     sys.exit(0)
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 test \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 test \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -278,7 +278,7 @@ if __name__ == "__main__":
 ''')
     sys.exit(0)
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 test \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 test \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -315,7 +315,7 @@ if __name__ == "__main__":
 ''')
     sys.exit(1)
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 test \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 test \
       --spawn_strategy=remote \
       --remote_executor=localhost:${worker_port} \
       --remote_cache=localhost:${worker_port} \
@@ -347,7 +347,7 @@ load("//a:rule.bzl", "empty")
 package(default_visibility = ["//visibility:public"])
 empty(name = 'test')
 EOF
-  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA1 build \
+  bazel --host_jvm_args=-Dbazel.DigestFunction=SHA256 build \
       --spawn_strategy=remote \
       --remote_cache=localhost:${worker_port} \
       --test_output=errors \
