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I'm using TLS_RSA_WITH_AES_256_GCM_SHA384 cipher suite. I tracked all handshake messages and successfully can decrypt the Client Finished message(I verified with wireshark).

When I try to calculate the Finished message my self, I can't get the same result as in the Finished message I just tracked.

I collected all messages (in my case Client_Hello, Server_Hello, Certificate, Server_Done, Client_Key_Exchange) and then use the following PRF(master_secret, finished_label, Hash(handshake_messages)) finished_label = "client finished"

When doing Hash(handshake_messages) I'm using the master_secret and SAH384

Also when collecting the data I'm taking only the message data (No TLS record - The first 5 bytes).

What am I doing wrong?

asked 20 Oct '16, 00:02

Gil%20Fefer's gravatar image

Gil Fefer
46225
accept rate: 100%


I just solved it. The following is wrong: When doing Hash(handshake_messages) I'm using the master_secret and SAH384

What should be done is digest using SHA384 and not Hash with the master_secret.

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answered 20 Oct '16, 00:21

Gil%20Fefer's gravatar image

Gil Fefer
46225
accept rate: 100%

I converted your comment to an answer and accepted it so that it will not be listed as an unanswered question anymore... Please read the FAQ for details.

(20 Oct '16, 04:14) SYN-bit ♦♦
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question asked: 20 Oct '16, 00:02

question was seen: 1,153 times

last updated: 20 Oct '16, 04:14

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