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- Code Examples
- =============
- Code Example For Symmetric Key Cipher Operation
- -----------------------------------------------
- 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.
- ::
- static int test_skcipher(void)
- {
- 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:
- crypto_free_skcipher(tfm);
- skcipher_request_free(req);
- kfree(data);
- return err;
- }
- Code Example For Use of Operational State Memory With SHASH
- -----------------------------------------------------------
- ::
- struct sdesc {
- struct shash_desc shash;
- char ctx[];
- };
- static struct sdesc *init_sdesc(struct crypto_shash *alg)
- {
- struct sdesc *sdesc;
- int size;
- size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
- sdesc = kmalloc(size, GFP_KERNEL);
- if (!sdesc)
- return ERR_PTR(-ENOMEM);
- sdesc->shash.tfm = alg;
- return sdesc;
- }
- static int calc_hash(struct crypto_shash *alg,
- const unsigned char *data, unsigned int datalen,
- unsigned char *digest)
- {
- struct sdesc *sdesc;
- int ret;
- sdesc = init_sdesc(alg);
- if (IS_ERR(sdesc)) {
- pr_info("can't alloc sdesc\n");
- return PTR_ERR(sdesc);
- }
- ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest);
- kfree(sdesc);
- return ret;
- }
- static int test_hash(const unsigned char *data, unsigned int datalen,
- unsigned char *digest)
- {
- struct crypto_shash *alg;
- char *hash_alg_name = "sha1-padlock-nano";
- int ret;
- alg = crypto_alloc_shash(hash_alg_name, 0, 0);
- if (IS_ERR(alg)) {
- pr_info("can't alloc alg %s\n", hash_alg_name);
- return PTR_ERR(alg);
- }
- ret = calc_hash(alg, data, datalen, digest);
- crypto_free_shash(alg);
- return ret;
- }
- Code Example For Random Number Generator Usage
- ----------------------------------------------
- ::
- static int get_random_numbers(u8 *buf, unsigned int len)
- {
- struct crypto_rng *rng = NULL;
- char *drbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */
- int ret;
- if (!buf || !len) {
- pr_debug("No output buffer provided\n");
- return -EINVAL;
- }
- rng = crypto_alloc_rng(drbg, 0, 0);
- if (IS_ERR(rng)) {
- pr_debug("could not allocate RNG handle for %s\n", drbg);
- return PTR_ERR(rng);
- }
- ret = crypto_rng_get_bytes(rng, buf, len);
- if (ret < 0)
- pr_debug("generation of random numbers failed\n");
- else if (ret == 0)
- pr_debug("RNG returned no data");
- else
- pr_debug("RNG returned %d bytes of data\n", ret);
- out:
- crypto_free_rng(rng);
- return ret;
- }
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