No authenticated encryption = ability to modify encrypted files about kindi HOT 3 CLOSED

For Go streams, it seems like it's better to append HMAC to the end of encrypted file. So:

Derive HMAC key:

1. Setup your cipher, as usual.
2. Encrypt 64 bytes of zeroes with this cipher.

Encrypt and authenticate:
3. Setup HMAC-SHA256 with bytes from step 2 as secret key.
4. Create a writer which first encrypts with the same cipher as used in steps 1-2, and then writes encrypted bytes to both output and HMAC (you can use io.MultiWriter here). (Basically, connect multiwriter{output, hmac} to cipher.StreamWriter.)

\5. Append hmac.Sum() to file.

For decryption, do 1-3, then in step 4 do HMAC and then decryption, and finally, compare hmac.Sum() with the one at the end of the file. If they are different, report error.

from kindi.

excellent. thanks very much. will do

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added HMAC for payload and for symmetric header part

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