In wireshark, I am able to see the encrypted data to and fro from my PC. It does not use diffie hellman algorihm for key exchange because I see only the Client Key Exchange packet but there is no Server Key Exchange packet. That means the browser is sending the encrypted key to the server(encrypted using the server's public key).
But I do not see any encrypted data in that packet("Client Key Exchange"). How to view the encrypted key?
1
votes
I'm somewhat surprised that you've chosen to accept an answer that doesn't actually answer your question, unless I've missed something...
– Bruno
@Bruno Now I got the right answer from right person and I Accepted it. Thanks for notifying me my mistake :)
– suraj
If you and @Ashwin have chosen to come on SO to give each other rep, don't bother (easy to see you respective profiles, including deleted answers). You were asking a very detailed question which requires a expertise an SSL (and assumes that someone asking it knew the basics of looking at packets). Admittedly, I though you were more interested of what had been encrypted, rather that just the result. Ashwin's answer is ridiculously trivial for someone who's trying to learn about SSL: it you can't remove the first 2 bytes (and use a recent version of Wireshark anyway), don't bother learning more.
– Bruno
As for un-upvoting and downvoting my correct answer, you guys are just cheeky, especially considering that Ashwin had asked even more details about the master secret itself (it's clear you two work on these questions together, which isn't a problem as such of course). Yes, I downvoted your question (and only this one), only because you didn't seem to make up your mind as to what you were asking (like you've done in many other questions about SSL or on security.SE).
– Bruno
3 Answers
8
votes
You won't see the encrypted shared-key, it's not exchanged. You can see the encrypted pre-master secret when using RSA authenticated key exchange. (Note that using Ephemeral Diffie-Hellman isn't the only reason for not seeing a server key exchange message: it could also use a DH_DSS or DH_RSA cipher suite, but this is unusual as far as I know).
If you follow the instructions about decrypting SSL with Wireshark, use the "SSL debug file" option to store the logs into a file. (Note that the user interface has changed slightly in newer versions of Wireshark, in the way you configure the private key.)
The log files will contain the pre-master secret and the shared keys.
(By the way, you need the server's private key to do this, of course.)
Using the sample data provided on the Wireshark page, you get:
pre master encrypted[128]:
65 51 2d a6 d4 a7 38 df ac 79 1f 0b d9 b2 61 7d
73 88 32 d9 f2 62 3a 8b 11 04 75 ca 42 ff 4e d9
cc b9 fa 86 f3 16 2f 09 73 51 66 aa 29 cd 80 61
0f e8 13 ce 5b 8e 0a 23 f8 91 5e 5f 54 70 80 8e
7b 28 ef b6 69 b2 59 85 74 98 e2 7e d8 cc 76 80
e1 b6 45 4d c7 cd 84 ce b4 52 79 74 cd e6 d7 d1
9c ad ef 63 6c 0f f7 05 e4 4d 1a d3 cb 9c d2 51
b5 61 cb ff 7c ee c7 bc 5e 15 a3 f2 52 0f bb 32
pre master secret[48]:
03 00 ff 84 56 6d a0 fb cc fd c6 c8 20 d5 f0 65
18 87 b0 44 45 9c e3 92 f0 4d 32 cd 41 85 10 24
cb 7a b3 01 36 3d 93 27 12 a4 7e 00 29 96 59 d8
master secret[48]:
1e db 35 95 b8 18 b3 52 58 f3 07 3f e6 af 8a a6
ab c3 a4 ed 66 3a 46 86 b6 e5 49 2a 7c f7 8c c2
ac 22 bb 13 15 0f d8 62 a2 39 23 7b c2 ff 28 fb
key expansion[136]:
11 60 e4 e1 74 e9 a1 cf 67 f9 b7 bc ef bc a7 c7
b3 f7 33 aa b2 42 d0 1c a6 4e fb e9 9b 13 dd 29
63 aa 17 1f 47 71 95 71 08 e0 4b 8e e1 da 7b 4a
5a f3 c2 32 bd e0 a5 82 6d 14 44 3a d6 cb 2d c0
7d 57 be a8 37 de 5d d9 a1 07 fd 1b 22 71 b9 4b
7a 1e 0f 70 37 14 97 0a f0 db 98 3b 7b 74 e3 2d
51 66 2e 31 68 90 ac 6f e6 53 3c c9 5e 48 0c 05
bc 9f 92 e7 f9 91 98 f5 95 1c c4 bf d9 cb 26 ef
35 70 5e ad 21 22 3e f6
Client MAC key[20]:
11 60 e4 e1 74 e9 a1 cf 67 f9 b7 bc ef bc a7 c7
b3 f7 33 aa
Server MAC key[20]:
b2 42 d0 1c a6 4e fb e9 9b 13 dd 29 63 aa 17 1f
47 71 95 71
Client Write key[32]:
08 e0 4b 8e e1 da 7b 4a 5a f3 c2 32 bd e0 a5 82
6d 14 44 3a d6 cb 2d c0 7d 57 be a8 37 de 5d d9
Server Write key[32]:
a1 07 fd 1b 22 71 b9 4b 7a 1e 0f 70 37 14 97 0a
f0 db 98 3b 7b 74 e3 2d 51 66 2e 31 68 90 ac 6f
Client Write IV[16]:
e6 53 3c c9 5e 48 0c 05 bc 9f 92 e7 f9 91 98 f5
Server Write IV[16]:
95 1c c4 bf d9 cb 26 ef 35 70 5e ad 21 22 3e f6
3
votes
Until recently the dissection of the ClientKeyExchange was like this(version 1.6 and below):
TLSv1 Record Layer: Handshake Protocol: Client Key Exchange
Content Type: Handshake (22)
Version: TLS 1.0 (0x0301)
Length: 134
Handshake Protocol: Client Key Exchange
Handshake Type: Client Key Exchange (16)
Length: 130
But if you use this verison(1.7.2 upwards) the key dissection will be like this:
TLSv1 Record Layer: Handshake Protocol: Client Key Exchange
Content Type: Handshake (22)
Version: TLS 1.0 (0x0301)
Length: 134
Handshake Protocol: Client Key Exchange
Handshake Type: Client Key Exchange (16)
Length: 130
RSA Encrypted PreMaster Secret
Encrypted PreMaster length: 128
Encrypted PreMaster: 761b1beac35e59de9a3bb9f74ebf9109b738e8ad346
You can see the encrypted pre-master:)
3
votes
Awesome write up here explaining how SSL works, notice at no time during this handshake is the private key ever sent over the wire.
http://4orensics.wordpress.com/2011/10/21/ssl-in-a-nutshell/
Long story short there is no way to decrypt SSL streams without the server's private key (unless you work for the NSA or something), however you may want to look into getting in between the server and client during the handshake and if the user does not check the validity of the certificate that is presented you are in business.
Here is a tool that can do that for you among many others
Of note I highly recommend the sans reading room article on SSL Mitm(Man in the Middle) attacks.
