crypto: aead - fix inaccurate documentation

The AEAD documentation conflates associated data and authentication
tags: the former (along with the ciphertext) is authenticated by the
latter. Fix the doc accordingly.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/aead.h

@@ -27,15 +27,12 @@
  *
  * For example: authenc(hmac(sha256), cbc(aes))
  *
- * The example code provided for the symmetric key cipher operation
- * applies here as well. Naturally all *skcipher* symbols must be exchanged
- * the *aead* pendants discussed in the following. In addition, for the AEAD
- * operation, the aead_request_set_ad function must be used to set the
- * pointer to the associated data memory location before performing the
- * encryption or decryption operation. In case of an encryption, the associated
- * data memory is filled during the encryption operation. For decryption, the
- * associated data memory must contain data that is used to verify the integrity
- * of the decrypted data. Another deviation from the asynchronous block cipher
+ * The example code provided for the symmetric key cipher operation applies
+ * here as well. Naturally all *skcipher* symbols must be exchanged the *aead*
+ * pendants discussed in the following. In addition, for the AEAD operation,
+ * the aead_request_set_ad function must be used to set the pointer to the
+ * associated data memory location before performing the encryption or
+ * decryption operation. Another deviation from the asynchronous block cipher
  * operation is that the caller should explicitly check for -EBADMSG of the
  * crypto_aead_decrypt. That error indicates an authentication error, i.e.
  * a breach in the integrity of the message. In essence, that -EBADMSG error
@@ -49,7 +46,10 @@
  *
  * The destination scatterlist has the same layout, except that the plaintext
  * (resp. ciphertext) will grow (resp. shrink) by the authentication tag size
- * during encryption (resp. decryption).
+ * during encryption (resp. decryption). The authentication tag is generated
+ * during the encryption operation and appended to the ciphertext. During
+ * decryption, the authentication tag is consumed along with the ciphertext and
+ * used to verify the integrity of the plaintext and the associated data.
  *
  * In-place encryption/decryption is enabled by using the same scatterlist
  * pointer for both the source and destination.