Chapter 6. Code Examples
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# Chapter 6. Code Examples

## Code Example For Asynchronous Block Cipher Operation

    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;
    }

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