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I've been studying encryption on a hobby basis, and wanted to know if I got this basic cypher construction right (this is another experiment, see the AES ECB experiment thread earlier).

Encryption:

  1. XOR plain text block, initialization vector and counter together.
  2. AES resulting block.
  3. Increment counter.
  4. Goto 1 until all plain text blocks are done.

Authentication tag:

  1. Sha256 cipher text.
  2. AES resulting hash using authentication key.
Thorham
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  • As to the first part, this will answer your question: http://crypto.stackexchange.com/questions/14782/why-does-ctr-mode-xor-the-plaintext-into-the-output-of-the-block-cipher-rather-t/14785#14785 – Richie Frame Mar 04 '15 at 20:21
  • For the second part, see http://crypto.stackexchange.com/questions/3229/is-the-encryption-of-a-hash-a-good-mac – Ilmari Karonen Mar 04 '15 at 21:03
  • Yeah, those posts explain it all. Thanks. It sure is easy to get this wrong. – Thorham Mar 05 '15 at 08:15
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    A common truth is: It is easy to design a scheme you can't break yourself. But it is an entirely different matter to design a scheme, which no one can break. – tylo Mar 05 '15 at 13:49

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