1 files changed, 12 insertions, 10 deletions
diff --git a/activesupport/lib/active_support/security_utils.rb b/activesupport/lib/active_support/security_utils.rb
index b6b31ef140..20b6b9cd3f 100644
--- a/activesupport/lib/active_support/security_utils.rb
+++ b/activesupport/lib/active_support/security_utils.rb
@@ -4,14 +4,12 @@ require "digest/sha2"
 
 module ActiveSupport
   module SecurityUtils
-    # Constant time string comparison.
+    # Constant time string comparison, for fixed length strings.
     #
     # The values compared should be of fixed length, such as strings
-    # that have already been processed by HMAC. This should not be used
-    # on variable length plaintext strings because it could leak length info
-    # via timing attacks.
-    def secure_compare(a, b)
-      return false unless a.bytesize == b.bytesize
+    # that have already been processed by HMAC. Raises in case of length mismatch.
+    def fixed_length_secure_compare(a, b)
+      raise ArgumentError, "string length mismatch." unless a.bytesize == b.bytesize
 
       l = a.unpack "C#{a.bytesize}"
 
@@ -19,11 +17,15 @@ module ActiveSupport
       b.each_byte { |byte| res |= byte ^ l.shift }
       res == 0
     end
-    module_function :secure_compare
+    module_function :fixed_length_secure_compare
 
-    def variable_size_secure_compare(a, b) # :nodoc:
-      secure_compare(::Digest::SHA256.hexdigest(a), ::Digest::SHA256.hexdigest(b))
+    # Constant time string comparison, for variable length strings.
+    #
+    # The values are first processed by SHA256, so that we don't leak length info
+    # via timing attacks.
+    def secure_compare(a, b)
+      fixed_length_secure_compare(::Digest::SHA256.hexdigest(a), ::Digest::SHA256.hexdigest(b)) && a == b
     end
-    module_function :variable_size_secure_compare
+    module_function :secure_compare
   end
 end