SSL decrypting with master secret but no session id

Question

RSA Session-ID:xxxx Master-Key:yyyy

Is one of the formats for decrypting SSL traffic if I have the master secret. But some sites like google don't send a Session-ID (Session Id Length 0). The other format for RSA based key exchange with the encrypted pre master key and pre master key I can't use because I don't have access to the pre master keys. As far as I understand trunk-1.10/epan/dissectors/packet-ssl-utils.c:

ssl_keylog_parse_session_id(...
if (ssl_session->session_id.data_len == 0)
    return FALSE;

as soon as the session id is 0, the format RSA Session-ID: Master-Key: isn't usable. Could someone confirm that or may be have an alternative solution (without modifying Wireshark)?

Accepted Answer

Simple solution for that problem, reduce the possible cipher suites to the suites supported by wireshark. You find the supported ones in epan/dissectors/packet-ssl-utils.c under static SslCipherSuite cipher_suites[]={

For example Qt (OpenSSL) :

wiresharkSupportedCipherSuites = ["EXP-RC4-MD5", "RC4-MD5", "RC4-SHA", "EXP-RC2-CBC-MD5", "IDEA-CBC-SHA", "EXP-DES-CBC-SHA", "DES-CBC3-SHA", "AES128-SHA", "DHE-DSS-AES128-SHA", "DHE-RSA-AES128-SHA", "AES256-SHA", "DHE-DSS-AES256-SHA", "DHE-RSA-AES256-SHA", "AES128-SHA256", "AES256-SHA256", "DHE-DSS-AES128-SHA256", "DHE-RSA-AES128-SHA256", "DHE-DSS-AES256-SHA256", "DHE-RSA-AES256-SHA256"]

The notation is a bit strange in Qt, took some time to compare the cipher suite names.

Answer 2

1

The SSL dissector will try 3 formats:

    if (ssl_keylog_parse_session_id(line, ssl_session) ||
        ssl_keylog_parse_rsa_premaster(line, ssl_session,
                                       encrypted_pre_master) ||
        ssl_keylog_parse_client_random(line, ssl_session)) {
        ret = 1;
        break;

The formats are:

RSA Session-ID:<hex session id> Master-Key:<hex TLS master secret>
RSA <hex, 8-bytes of encrypted pre-master secret> <hex pre-master secret>
CLIENT_RANDOM <hex client_random> <hex TLS master secret>

So if you can index your master secret with the client random for the session, you can still use the out-of-box functionality of wireshark 1.10. If not, a change to the code will be necessary.

Out-of-curiosity: Which application/library are you using to log the master-secret?

answered 27 Aug '13, 03:34

SYN-bit ♦♦
17.1k●9●57●245
accept rate: 20%

I tried the CLIENT_RANDOM but it doesn't work for me (for RSA based key exchange).

I use QtWebkit with a modified Qt library. It's easy to modify and recompile Qt if you use the source package of your distribution. In qsslsocket_openssl.cpp (Qt source package) you find some commented lines for writing a file with the master secrets.

(27 Aug '13, 04:10) Jack Norris

Could that be the problem that CLIENT_RANDOM doesn't work:

dissect_ssl3_hnd_srv_hello can't find cipher suite 0x9C

I checked the packet-ssl-utils.c file and cipher suite 0x9C (TLS_RSA_WITH_AES_128_GCM_SHA256) should be present in Wireshark

dissect_ssl enter frame #18 (first time)
  conversation = 0x7f825d2d04b0, ssl_session = 0x7f825d2d0ac0
  record: offset = 0, reported_length_remaining = 1418
dissect_ssl3_record found version 0x0303(TLS 1.2) -> state 0x11
dissect_ssl3_record: content_type 22 Handshake
decrypt_ssl3_record: app_data len 62, ssl state 0x11
packet_from_server: is from server - TRUE
decrypt_ssl3_record: using server decoder
decrypt_ssl3_record: no decoder available
dissect_ssl3_handshake iteration 1 type 2 offset 5 length 58 bytes, remaining 67 
dissect_ssl3_hnd_hello_common found SERVER RANDOM -> state 0x13
ssl_restore_session can't find stored session
trying to use SSL keylog in /home/jim/Projects/Browser/pcaps/ssl-master-keys
  checking keylog line: RSA Session-ID:95DCDB01178B16AED12D269495048F60625A16904868D38DEDF0F751576A7B5B Master-Key:B5044BA33AD5BF283D1B04483480812B57173DFDD40757C729B33E2F7B796F12529A3E9A6B10C8C724904FAA3B3A5D4E
    line does not match
  checking keylog line: CLIENT_RANDOM 521C962164B2D2DB7349E44B80F49AF27AAD2CF84DC3369DC1C08C8C1CEB35D6 B5044BA33AD5BF283D1B04483480812B57173DFDD40757C729B33E2F7B796F12529A3E9A6B10C8C724904FAA3B3A5D4E
found master secret in key log
  cannot find master secret in keylog file either
dissect_ssl3_hnd_srv_hello can't find cipher suite 0x9C
  record: offset = 67, reported_length_remaining = 1351
  need_desegmentation: offset = 67, reported_length_remaining = 1351

(27 Aug '13, 05:49) Jack Norris

@Jack Norris The GCM cipher suite is supported in the development version (1.11.0 or newer).

(15 Dec '13, 12:09) Lekensteyn

@Lekensteyn This is great news! Thank you for this information!

(22 Dec '13, 16:00) Jack Norris