We default to using aes-256-cbc as our verification/signing cipher. It can accept key lengths of 128, 192 or 256-bit, whereas currently we were providing twice the acceptable value.

ruby < 2.4 allowed accepting these values, as extra key bits were ignored. Since https://github.com/ruby/ruby/commit/ce635262f53b760284d56bb1027baebaaec175d1 this now has a strict checking on key length.

Default to key length 32 bytes, to match the compatible length for  aes-256-cbc

Fixes #25185

1 files changed, 4 insertions, 6 deletions

diff --git a/activesupport/lib/active_support/key_generator.rb b/activesupport/lib/active_support/key_generator.rb
index 7f73f9ddfc..7eafbb571f 100644
--- a/activesupport/lib/active_support/key_generator.rb
+++ b/activesupport/lib/active_support/key_generator.rb
@@ -15,9 +15,8 @@ module ActiveSupport
     end
 
     # Returns a derived key suitable for use.  The default key_size is chosen
-    # to be compatible with the default settings of ActiveSupport::MessageVerifier.
-    # i.e. OpenSSL::Digest::SHA1#block_length
-    def generate_key(salt, key_size=64)
+    # to be compatible with the acceptable key length of aes-256-cbc, the default cipher.
+    def generate_key(salt, key_size=32)
       OpenSSL::PKCS5.pbkdf2_hmac_sha1(@secret, salt, @iterations, key_size)
     end
   end
@@ -32,9 +31,8 @@ module ActiveSupport
     end
 
     # Returns a derived key suitable for use.  The default key_size is chosen
-    # to be compatible with the default settings of ActiveSupport::MessageVerifier.
-    # i.e. OpenSSL::Digest::SHA1#block_length
-    def generate_key(salt, key_size=64)
+    # to be compatible with the acceptable key length of aes-256-cbc, the default cipher.
+    def generate_key(salt, key_size=32)
       @cache_keys["#{salt}#{key_size}"] ||= @key_generator.generate_key(salt, key_size)
     end
   end