06_Code_Examples.txt

== Code Examples

=== Code Example For Asynchronous Block Cipher Operation

[source,c]
-----------------
struct tcrypt_result {
	struct completion completion;
	int err;
};

/* tie all data structures together */
struct ablkcipher_def {
	struct scatterlist sg;
	struct crypto_ablkcipher *tfm;
	struct ablkcipher_request *req;
	struct tcrypt_result result;
};

/* Callback function */
static void test_ablkcipher_cb(struct crypto_async_request *req, int error)
{
	struct tcrypt_result *result = req->data;

	if (error == -EINPROGRESS)
		return;
	result->err = error;
	complete(&result->completion);
	pr_info("Encryption finished successfully\n");
}

/* Perform cipher operation */
static unsigned int test_ablkcipher_encdec(struct ablkcipher_def *ablk,
					   int enc)
{
	int rc = 0;

	if (enc)
		rc = crypto_ablkcipher_encrypt(ablk->req);
	else
		rc = crypto_ablkcipher_decrypt(ablk->req);

	switch (rc) {
	case 0:
		break;
	case -EINPROGRESS:
	case -EBUSY:
		rc = wait_for_completion_interruptible(
			&ablk->result.completion);
		if (!rc && !ablk->result.err) {
			reinit_completion(&ablk->result.completion);
			break;
		}
	default:
		pr_info("ablkcipher encrypt returned with %d result %d\n",
		       rc, ablk->result.err);
		break;
	}
	init_completion(&ablk->result.completion);

	return rc;
}

/* Initialize and trigger cipher operation */
static int test_ablkcipher(void)
{
	struct ablkcipher_def ablk;
	struct crypto_ablkcipher *ablkcipher = NULL;
	struct ablkcipher_request *req = NULL;
	char *scratchpad = NULL;
	char *ivdata = NULL;
	unsigned char key[32];
	int ret = -EFAULT;

	ablkcipher = crypto_alloc_ablkcipher("cbc-aes-aesni", 0, 0);
	if (IS_ERR(ablkcipher)) {
		pr_info("could not allocate ablkcipher handle\n");
		return PTR_ERR(ablkcipher);
	}

	req = ablkcipher_request_alloc(ablkcipher, GFP_KERNEL);
	if (IS_ERR(req)) {
		pr_info("could not allocate request queue\n");
		ret = PTR_ERR(req);
		goto out;
	}

	ablkcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
					test_ablkcipher_cb,
					&ablk.result);

	/* AES 256 with random key */
	get_random_bytes(&key, 32);
	if (crypto_ablkcipher_setkey(ablkcipher, 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);

	ablk.tfm = ablkcipher;
	ablk.req = req;

	/* We encrypt one block */
	sg_init_one(&ablk.sg, scratchpad, 16);
	ablkcipher_request_set_crypt(req, &ablk.sg, &ablk.sg, 16, ivdata);
	init_completion(&ablk.result.completion);

	/* encrypt data */
	ret = test_ablkcipher_encdec(&ablk, 1);
	if (ret)
		goto out;

	pr_info("Encryption triggered successfully\n");

out:
	if (ablkcipher)
		crypto_free_ablkcipher(ablkcipher);
	if (req)
		ablkcipher_request_free(req);
	if (ivdata)
		kfree(ivdata);
	if (scratchpad)
		kfree(scratchpad);
	return ret;
}
-----------------

=== Code Example For Synchronous Block Cipher Operation

[source,c]
--------------------
static int test_blkcipher(void)
{
	struct crypto_blkcipher *blkcipher = NULL;
	char *cipher = "cbc(aes)";
	// AES 128
	charkey =
"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
	chariv =
"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
	unsigned int ivsize = 0;
	char *scratchpad = NULL; // holds plaintext and ciphertext
	struct scatterlist sg;
	struct blkcipher_desc desc;
	int ret = -EFAULT;

	blkcipher = crypto_alloc_blkcipher(cipher, 0, 0);
	if (IS_ERR(blkcipher)) {
		printk("could not allocate blkcipher handle for %s\n", cipher);
		return -PTR_ERR(blkcipher);
	}

	if (crypto_blkcipher_setkey(blkcipher, key, strlen(key))) {
		printk("key could not be set\n");
		ret = -EAGAIN;
		goto out;
	}

	ivsize = crypto_blkcipher_ivsize(blkcipher);
	if (ivsize) {
		if (ivsize != strlen(iv))
			printk("IV length differs from expected length\n");
		crypto_blkcipher_set_iv(blkcipher, iv, ivsize);
	}

	scratchpad = kmalloc(crypto_blkcipher_blocksize(blkcipher), GFP_KERNEL);
	if (!scratchpad) {
		printk("could not allocate scratchpad for %s\n", cipher);
		goto out;
	}
	/* get some random data that we want to encrypt */
	get_random_bytes(scratchpad, crypto_blkcipher_blocksize(blkcipher));

	desc.flags = 0;
	desc.tfm = blkcipher;
	sg_init_one(&sg, scratchpad, crypto_blkcipher_blocksize(blkcipher));

	/* encrypt data in place */
	crypto_blkcipher_encrypt(&desc, &sg, &sg,
				 crypto_blkcipher_blocksize(blkcipher));

	/* decrypt data in place
	 * crypto_blkcipher_decrypt(&desc, &sg, &sg,
	 */			 crypto_blkcipher_blocksize(blkcipher));


	printk("Cipher operation completed\n");
	return 0;

out:
	if (blkcipher)
		crypto_free_blkcipher(blkcipher);
	if (scratchpad)
		kzfree(scratchpad);
	return ret;
}
--------------------

=== Code Example For Use of Operational State Memory With SHASH

[source,c]
-------------------
struct sdesc {
	struct shash_desc shash;
	char ctx[];
};

static struct sdescinit_sdesc(struct crypto_shash *alg)
{
	struct sdescsdesc;
	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;
	sdesc->shash.flags = 0x0;
	return sdesc;
}

static int calc_hash(struct crypto_shashalg,
		     const unsigned chardata, unsigned int datalen,
		     unsigned chardigest) {
	struct sdescsdesc;
	int ret;

	sdesc = init_sdesc(alg);
	if (IS_ERR(sdesc)) {
		pr_info("trusted_key: can't alloc %s\n", hash_alg);
		return PTR_ERR(sdesc);
	}

	ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest);
	kfree(sdesc);
	return ret;
}
-------------------

=== Code Example For Random Number Generator Usage

[source,c]
----------------
static int get_random_numbers(u8 *buf, unsigned int len)
{
	struct crypto_rngrng = NULL;
	chardrbg = "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;
}
----------------