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When running the command: openssl ciphers -v I get a long list of cipher combinations. I'm having issues interpreting some of them. An example is:

DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(256) Mac=AEAD

I thought the last part of the combination, in this case SHA384 would be the HMAC function. It seems it's been replaced by AEAD instead. Reading up on Authenticated Encryption with Associated Data (AEAD) it seems to be a class of block cipher modes, not a specific HMAC function.

Could someone explain this further? Is SHA384 one of these modes? Is SHA384 used in the AES encryption somehow and then that algorithm re-used for the MAC?

span
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1 Answers1

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Mostly(?) duplicate of What's the hash for in ECDHE-RSA-AES-GCM-SHA?

TLSv1.2 adds a new class of ciphers using AEAD modes such as GCM, which is a single crypto operation that does both encryption and integrity protection, instead of having separate encryption and HMAC e.g. AES128-CBC plus HMAC-SHA1. Mac=AEAD means really no HMAC is needed because of AEAD. However, TLSv1.2 also changes the PRF (key derivation) to use varying SHA-2 hashes (instead of always SHA-1 and MD5) so the hash is still specified in the ciphersuite.

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dave_thompson_085
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