![]() My question is, how do I calculate label?Īs RFC mentions, "+" denotes concatenation, but concatenation of whatĪnd other thing to mention, TLSCompressed.version means: Hmac.new(,label+message,hashlib.sha256).digest() HMAC_SHA256 calculation, in python, is as follows: import hashlib seq_number is 1 as it's the first message.message length is 1122, removing preceding IV, offset and MAC verification, message, gets a final length of 1122.message version is 0x0303 as it's TLS 1.2.message_type is 0x17, because as an Application_data message type, the correct value should be 0x17. ![]() client_mac is extracted from keyring_material. ![]() Taking this as an example: Chosen cipher_suite is TLS_RSA_WITH_AES_256_CBC_SHA256Įncrypted_message_length = 1184 (IV|Message|MAC|Offset)ĭecrypted_message_length = 1122 (removing IV, MAC and offset) TLSCompressed.version + TLSCompressed.length + ![]() The MAC is generated as: HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type + When I receive the first Application_Data message (0x17), I am able to decrypt it, but unable to verify message integrity. I've extracted all keyring related material (client IV, MAC, Key and Server IV, MAC, key). I'm developing a SSL de-cipher in python but I'm having some problems on HMAC verification:
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