0

I can't seem to correctly decrypt a SSL 1.2 Finished message.

I have correctly generated the master key, and therefore I am confident that my PRF implementation is correct.

To generate the keying material:

PRF(master_secret, 'key expansion', seed)

  • I take 16 bytes (128 bits) for client_write_MAC_key (MD5)
  • I then take 16 bytes (128 bits) for server_write_MAC_key (MD5)
  • I then take 5 bytes (40 bits) for client_write_key (RC4-40)
  • I then take 5 bytes (40 bits) for server_write_key (RC4-40)

I extract the encrypted handshake from Wireshark and attempt to decrypt it using RC4 with a 5 byte key (EXP-RC4-MD5). The decrypted output is not formatted as expected. The first byte of data I should see is the content type, which should be 14 for the Finished message, I do not see this. Is there anything incorrect about what I have said thus far?

1

The key generation function described in RFC 5246 is not applicable to this cipher suite, which is why I was unable to decrypt the message. Having reimplemented the key generation function described in RFC 2246 (TLS 1.0) I am now able to successfully decrypt the Finished message.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.