digest_length_in_hex

# File activesupport/lib/active_support/message_verifier.rb, line 335
      def digest_length_in_hex
        # In hexadecimal (AKA base16) it takes 4 bits to represent a character,
        # hence we multiply the digest's length (in bytes) by 8 to get it in
        # bits and divide by 4 to get its number of characters it hex. Well, 8
        # divided by 4 is 2.
        @digest_length_in_hex ||= OpenSSL::Digest.new(@digest).digest_length * 2
      end