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’sassumed 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;}