Code Examples

Code Example For Symmetric Key Cipher Operation

struct tcrypt_result {
    struct completion completion;
    int err;
};

/* tie all data structures together */
struct skcipher_def {
    struct scatterlist sg;
    struct crypto_skcipher *tfm;
    struct skcipher_request *req;
    struct tcrypt_result result;
};

/* Callback function */
static void test_skcipher_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_skcipher_encdec(struct skcipher_def *sk,
                     int enc)
{
    int rc = 0;

    if (enc)
        rc = crypto_skcipher_encrypt(sk->req);
    else
        rc = crypto_skcipher_decrypt(sk->req);

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

    return rc;
}

/* Initialize and trigger cipher operation */
static int test_skcipher(void)
{
    struct skcipher_def sk;
    struct crypto_skcipher *skcipher = NULL;
    struct skcipher_request *req = NULL;
    char *scratchpad = NULL;
    char *ivdata = NULL;
    unsigned char key[32];
    int ret = -EFAULT;

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

    req = skcipher_request_alloc(skcipher, GFP_KERNEL);
    if (!req) {
        pr_info("could not allocate skcipher request\n");
        ret = -ENOMEM;
        goto out;
    }

    skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
                      test_skcipher_cb,
                      &sk.result);

    /* AES 256 with random key */
    get_random_bytes(&key, 32);
    if (crypto_skcipher_setkey(skcipher, 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);

    sk.tfm = skcipher;
    sk.req = req;

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

    /* encrypt data */
    ret = test_skcipher_encdec(&sk, 1);
    if (ret)
        goto out;

    pr_info("Encryption triggered successfully\n");

out:
    if (skcipher)
        crypto_free_skcipher(skcipher);
    if (req)
        skcipher_request_free(req);
    if (ivdata)
        kfree(ivdata);
    if (scratchpad)
        kfree(scratchpad);
    return ret;
}

Code Example For Use of Operational State Memory With SHASH

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

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;
}