Chapter 6. Code Examples

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;
}