From: Eric Biggers <ebiggers@xxxxxxxxxx> Properly document the scatterlist layout for AEAD ciphers. Reported-by: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx> Cc: Stephan Mueller <smueller@xxxxxxxxxx> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- include/crypto/aead.h | 48 ++++++++++++++++++++++++------------------- 1 file changed, 27 insertions(+), 21 deletions(-) diff --git a/include/crypto/aead.h b/include/crypto/aead.h index 1b3ebe8593c0..62c68550aab6 100644 --- a/include/crypto/aead.h +++ b/include/crypto/aead.h @@ -43,27 +43,33 @@ * * Memory Structure: * - * To support the needs of the most prominent user of AEAD ciphers, namely - * IPSEC, the AEAD ciphers have a special memory layout the caller must adhere - * to. - * - * The scatter list pointing to the input data must contain: - * - * * for RFC4106 ciphers, the concatenation of - * associated authentication data || IV || plaintext or ciphertext. Note, the - * same IV (buffer) is also set with the aead_request_set_crypt call. Note, - * the API call of aead_request_set_ad must provide the length of the AAD and - * the IV. The API call of aead_request_set_crypt only points to the size of - * the input plaintext or ciphertext. - * - * * for "normal" AEAD ciphers, the concatenation of - * associated authentication data || plaintext or ciphertext. - * - * It is important to note that if multiple scatter gather list entries form - * the input data mentioned above, the first entry must not point to a NULL - * buffer. If there is any potential where the AAD buffer can be NULL, the - * calling code must contain a precaution to ensure that this does not result - * in the first scatter gather list entry pointing to a NULL buffer. + * The source scatterlist must contain the concatenation of + * associated data || plaintext or ciphertext. + * + * 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). + * + * In-place encryption/decryption is enabled by using the same scatterlist + * pointer for both the source and destination. + * + * Even in the out-of-place case, space must be reserved in the destination for + * the associated data, even though it won't be written to. This makes the + * in-place and out-of-place cases more consistent. It is permissible for the + * "destination" associated data to alias the "source" associated data. + * + * As with the other scatterlist crypto APIs, zero-length scatterlist elements + * are not allowed in the used part of the scatterlist. Thus, if there is no + * associated data, the first element must point to the plaintext/ciphertext. + * + * To meet the needs of IPsec, a special quirk applies to rfc4106, rfc4309, + * rfc4543, and rfc7539esp ciphers. For these ciphers, the final 'ivsize' bytes + * of the associated data buffer must contain a second copy of the IV. This is + * in addition to the copy passed to aead_request_set_crypt(). These two IV + * copies must not differ; different implementations of the same algorithm may + * behave differently in that case. Note that the algorithm might not actually + * treat the IV as associated data; nevertheless the length passed to + * aead_request_set_ad() must include it. */ struct crypto_aead; -- 2.25.1
