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Diffstat (limited to 'Documentation/crypto/api-samples.rst')
| -rw-r--r-- | Documentation/crypto/api-samples.rst | 176 |
1 files changed, 77 insertions, 99 deletions
diff --git a/Documentation/crypto/api-samples.rst b/Documentation/crypto/api-samples.rst index f14afaaf2f32..e923f17bc2bd 100644 --- a/Documentation/crypto/api-samples.rst +++ b/Documentation/crypto/api-samples.rst @@ -4,111 +4,89 @@ Code Examples Code Example For Symmetric Key Cipher Operation ----------------------------------------------- -:: - - - /* tie all data structures together */ - struct skcipher_def { - struct scatterlist sg; - struct crypto_skcipher *tfm; - struct skcipher_request *req; - struct crypto_wait wait; - }; - - /* Perform cipher operation */ - static unsigned int test_skcipher_encdec(struct skcipher_def *sk, - int enc) - { - int rc; - - if (enc) - rc = crypto_wait_req(crypto_skcipher_encrypt(sk->req), &sk->wait); - else - rc = crypto_wait_req(crypto_skcipher_decrypt(sk->req), &sk->wait); - - if (rc) - pr_info("skcipher encrypt returned with result %d\n", rc); +This code encrypts some data with AES-256-XTS. For sake of example, +all inputs are random bytes, the encryption is done in-place, and it's +assumed the code is running in a context where it can sleep. - return rc; - } +:: - /* Initialize and trigger cipher operation */ static int test_skcipher(void) { - struct skcipher_def sk; - struct crypto_skcipher *skcipher = NULL; - struct skcipher_request *req = NULL; - char *scratchpad = NULL; - char *ivdata = NULL; - unsigned char key[32]; - int ret = -EFAULT; - - skcipher = crypto_alloc_skcipher("cbc-aes-aesni", 0, 0); - if (IS_ERR(skcipher)) { - pr_info("could not allocate skcipher handle\n"); - return PTR_ERR(skcipher); - } - - req = skcipher_request_alloc(skcipher, GFP_KERNEL); - if (!req) { - pr_info("could not allocate skcipher request\n"); - ret = -ENOMEM; - goto out; - } - - skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG, - crypto_req_done, - &sk.wait); - - /* AES 256 with random key */ - get_random_bytes(&key, 32); - if (crypto_skcipher_setkey(skcipher, key, 32)) { - pr_info("key could not be set\n"); - ret = -EAGAIN; - goto out; - } - - /* IV will be random */ - ivdata = kmalloc(16, GFP_KERNEL); - if (!ivdata) { - pr_info("could not allocate ivdata\n"); - goto out; - } - get_random_bytes(ivdata, 16); - - /* Input data will be random */ - scratchpad = kmalloc(16, GFP_KERNEL); - if (!scratchpad) { - pr_info("could not allocate scratchpad\n"); - goto out; - } - get_random_bytes(scratchpad, 16); - - sk.tfm = skcipher; - sk.req = req; - - /* We encrypt one block */ - sg_init_one(&sk.sg, scratchpad, 16); - skcipher_request_set_crypt(req, &sk.sg, &sk.sg, 16, ivdata); - crypto_init_wait(&sk.wait); - - /* encrypt data */ - ret = test_skcipher_encdec(&sk, 1); - if (ret) - goto out; - - pr_info("Encryption triggered successfully\n"); - + struct crypto_skcipher *tfm = NULL; + struct skcipher_request *req = NULL; + u8 *data = NULL; + const size_t datasize = 512; /* data size in bytes */ + struct scatterlist sg; + DECLARE_CRYPTO_WAIT(wait); + u8 iv[16]; /* AES-256-XTS takes a 16-byte IV */ + u8 key[64]; /* AES-256-XTS takes a 64-byte key */ + int err; + + /* + * Allocate a tfm (a transformation object) and set the key. + * + * In real-world use, a tfm and key are typically used for many + * encryption/decryption operations. But in this example, we'll just do a + * single encryption operation with it (which is not very efficient). + */ + + tfm = crypto_alloc_skcipher("xts(aes)", 0, 0); + if (IS_ERR(tfm)) { + pr_err("Error allocating xts(aes) handle: %ld\n", PTR_ERR(tfm)); + return PTR_ERR(tfm); + } + + get_random_bytes(key, sizeof(key)); + err = crypto_skcipher_setkey(tfm, key, sizeof(key)); + if (err) { + pr_err("Error setting key: %d\n", err); + goto out; + } + + /* Allocate a request object */ + req = skcipher_request_alloc(tfm, GFP_KERNEL); + if (!req) { + err = -ENOMEM; + goto out; + } + + /* Prepare the input data */ + data = kmalloc(datasize, GFP_KERNEL); + if (!data) { + err = -ENOMEM; + goto out; + } + get_random_bytes(data, datasize); + + /* Initialize the IV */ + get_random_bytes(iv, sizeof(iv)); + + /* + * Encrypt the data in-place. + * + * For simplicity, in this example we wait for the request to complete + * before proceeding, even if the underlying implementation is asynchronous. + * + * To decrypt instead of encrypt, just change crypto_skcipher_encrypt() to + * crypto_skcipher_decrypt(). + */ + sg_init_one(&sg, data, datasize); + skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG | + CRYPTO_TFM_REQ_MAY_SLEEP, + crypto_req_done, &wait); + skcipher_request_set_crypt(req, &sg, &sg, datasize, iv); + err = crypto_wait_req(crypto_skcipher_encrypt(req), &wait); + if (err) { + pr_err("Error encrypting data: %d\n", err); + goto out; + } + + pr_debug("Encryption was successful\n"); out: - if (skcipher) - crypto_free_skcipher(skcipher); - if (req) + crypto_free_skcipher(tfm); skcipher_request_free(req); - if (ivdata) - kfree(ivdata); - if (scratchpad) - kfree(scratchpad); - return ret; + kfree(data); + return err; } |