In my work I want to use the aes-gcm algorithm to encrypt data in linux kernel module, so I choose the aead api. In aes gcm the aad data can be setted 0-264 bits,but in the code if i use aead_request_set_ad() function set the data of scatterlist struct is null it will be error. AES-GCM algorithm
next it's my code in linux kernel 4.10:
int aes_gcm_decrypt(struct crypto_aead *tfm, u8 *j_0, u8 *aad,
u8 *data, size_t data_len, u8 *mic)
{
struct scatterlist sg[3];
struct aead_request *aead_req;
int reqsize = sizeof(*aead_req) + crypto_aead_reqsize(tfm);
int err;
if (data_len == 0)
return -EINVAL;
aead_req = kzalloc(reqsize + GCM_AAD_LEN, GFP_ATOMIC);
if (!aead_req)
return -ENOMEM;
sg_init_table(sg, 3);
sg_set_buf(&sg[0], aad,0);
sg_set_buf(&sg[1], data, data_len);
sg_set_buf(&sg[2], mic, 16);
aead_request_set_tfm(aead_req, tfm);
aead_request_set_crypt(aead_req, sg, sg,
data_len + 16, j_0);
aead_request_set_ad(aead_req, sg[0].length);
err = crypto_aead_decrypt(aead_req);
kzfree(aead_req);
return err;
}
And if I use sg_set_page(&sg[0], ZERO_PAGE(0), 0, 0) to set sg[0] it's also wrong.
And if I remove the sg[0] is's also wrong...
In aead_request_set_crypt function the annotations just like this:
/**
* aead_request_set_crypt - set data buffers
* @req: request handle
* @src: source scatter / gather list
* @dst: destination scatter / gather list
* @cryptlen: number of bytes to process from @src
* @iv: IV for the cipher operation which must comply with the IV size defined
* by crypto_aead_ivsize()
*
* Setting the source data and destination data scatter / gather lists which
* hold the associated data concatenated with the plaintext or ciphertext. See
* below for the authentication tag.
*
* For encryption, the source is treated as the plaintext and the
* destination is the ciphertext. For a decryption operation, the use is
* reversed - the source is the ciphertext and the destination is the plaintext.
*
* The memory structure for cipher operation has the following structure:
*
* - AEAD encryption input: assoc data || plaintext
* - AEAD encryption output: assoc data || cipherntext || auth tag
* - AEAD decryption input: assoc data || ciphertext || auth tag
* - AEAD decryption output: assoc data || plaintext
*
* Albeit the kernel requires the presence of the AAD buffer, however,
* the kernel does not fill the AAD buffer in the output case. If the
* caller wants to have that data buffer filled, the caller must either
* use an in-place cipher operation (i.e. same memory location for
* input/output memory location).
*/
The assoc data is must be existense, so how can i set it's length is zero??
I have solved this problem myself.just like this:
just define two scatterlist struct and set the ad zero.