TLS cipher suite using AES_CBC for encryption and SHA-2 for integrity defines that: first we have to calculate SHA-2 digest over the message then we can encrypt it with AES CBC mode cipher. Why we cannot pipeline two operations in one pass over the message ?

  • Can you please give the exact phrase and context of this definition? My guess it is only about order (MAC-then-Encrypt vs. Encrypt-then-MAC) and does not prohibit parallelism as long as the result is the same. – Steffen Ullrich Jul 11 '17 at 9:25
  • Not sure what you mean by "pipeline two operations in one pass". To me pipeline means do x then do y. If that is certain, then "one pass" (or more) has no impact. My understanding is that MAC-then-Encrypt is the sequence expected - since the integrity property is that of the message (plaintext), not the encrypted message (ciphertext). Given this, I'm not sure whether / how parallelism would work. – Sas3 Jul 11 '17 at 10:49
  • i meant after HMAC has been calculated over first block such block may be passed to encryption while HMAC continues with a second one – Elena Gurevich Jul 13 '17 at 8:17

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