Hello everyone,
I'm currently in the middle of debugging a
painful SSL issue. With the same client server combination we sometimes
suffer SSL handshaking errors and other times we don't. When things go
wrong the server (Active Directory) closes the connection without
sending a response. The only clue in the AD logs is an error 960 and 20.
Which I believe corresponds to a bad_record_mac.
The cipher is TLS_RSA_WITH_AES_128_CBC_SHA
What I have
noticed, is that when everything is OK, Wireshark can decrypt (using the
servers private key) the SSL handshake no problem, note this line from
the output:
ssl_decrypt_pre_master_secret:
RSA_private_decrypt
pcry_private_decrypt: stripping 207 bytes, decr_len 255
decrypted_unstrip_pre_master[255]:
pre master secret[48]:
When everything isn't ok, the SSL decryption fails:
ssl_decrypt_pre_master_secret:RSA_private_decrypt
pcry_private_decrypt: stripping 146 bytes, decr_len 255
decrypted_unstrip_pre_master[255]:
<snip>
ssl_decrypt_pre_master_secret wrong pre_master_secret length (109, expected 48)
dissect_ssl3_handshake can't decrypt pre master secret
Now I am
no SSL expert, but I don't think this is right. What I hope to
understand and the reason for this post, is how exactly the byte
stripping works... where does the SSL decrypter get 146 from and could
this explain our SSL issues? If so, what exactly is going wrong? I've
had a bit of a look through the TLS spec but it isn't clear to me and so
I would appreciate any and all advice.
Thanks,
Wayne.