Correct sequence for AEAD incremental functions

* denotes zero or more repeats.

Incremental encryption pseudocode

InitKey(key)
{ For each packet do:
   SetNonce(nonce)
   { AddAAD(aad-chunk) }*
   StartEncrypt()
   { ciphertext-chunk <-- Update(plaintext-chunk) }*
   tag <-- FinishEncrypt()
}*
Destroy()

Incremental decryption pseudocode

InitKey(key)
{ For each packet do:
   SetNonce(nonce)
   { AddAAD(aad-chunk) }*
   StartDecrypt(tag-to-check)
   { plaintext-chunk <-- Update(ciphertext-chunk) }*
   (OK|FAIL) <-- FinishDecrypt()
}*
Destroy()

Notes on incremental mode:

• AAD data must be added in its entirety before starting to encrypt or decrypt
• When decrypting in an incremental manner, the deciphered plaintext is output in chunks as the ciphertext chunks are added. Treat this plaintext as suspect until the AEAD_FinishDecrypt returns either OK or FAIL and throw it all away if FAIL is returned.
• All AEAD incremental functions return zero on success (except AEAD_InitKey). Using an incremental function out of sequence will return a MISUSE_ERROR error code.
• Calling AEAD_InitKey at any time will delete any existing state ready to start again with the same key. AEAD_Destroy is similar except all state including the key is destroyed.

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