| 1 | Code Examples
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| 2 | =============
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| 3 |
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| 4 | Code Example For Symmetric Key Cipher Operation
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| 5 | -----------------------------------------------
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| 6 |
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| 7 | This code encrypts some data with AES-256-XTS. For sake of example,
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| 8 | all inputs are random bytes, the encryption is done in-place, and it's
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| 9 | assumed the code is running in a context where it can sleep.
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| 10 |
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| 11 | ::
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| 12 |
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| 13 | static int test_skcipher(void)
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| 14 | {
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| 15 | struct crypto_skcipher *tfm = NULL;
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| 16 | struct skcipher_request *req = NULL;
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| 17 | u8 *data = NULL;
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| 18 | const size_t datasize = 512; /* data size in bytes */
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| 19 | struct scatterlist sg;
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| 20 | DECLARE_CRYPTO_WAIT(wait);
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| 21 | u8 iv[16]; /* AES-256-XTS takes a 16-byte IV */
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| 22 | u8 key[64]; /* AES-256-XTS takes a 64-byte key */
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| 23 | int err;
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| 24 |
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| 25 | /*
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| 26 | * Allocate a tfm (a transformation object) and set the key.
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| 27 | *
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| 28 | * In real-world use, a tfm and key are typically used for many
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| 29 | * encryption/decryption operations. But in this example, we'll just do a
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| 30 | * single encryption operation with it (which is not very efficient).
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| 31 | */
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| 32 |
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| 33 | tfm = crypto_alloc_skcipher("xts(aes)", 0, 0);
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| 34 | if (IS_ERR(tfm)) {
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| 35 | pr_err("Error allocating xts(aes) handle: %ld\n", PTR_ERR(tfm));
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| 36 | return PTR_ERR(tfm);
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| 37 | }
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| 38 |
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| 39 | get_random_bytes(key, sizeof(key));
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| 40 | err = crypto_skcipher_setkey(tfm, key, sizeof(key));
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| 41 | if (err) {
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| 42 | pr_err("Error setting key: %d\n", err);
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| 43 | goto out;
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| 44 | }
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| 45 |
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| 46 | /* Allocate a request object */
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| 47 | req = skcipher_request_alloc(tfm, GFP_KERNEL);
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| 48 | if (!req) {
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| 49 | err = -ENOMEM;
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| 50 | goto out;
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| 51 | }
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| 52 |
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| 53 | /* Prepare the input data */
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| 54 | data = kmalloc(datasize, GFP_KERNEL);
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| 55 | if (!data) {
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| 56 | err = -ENOMEM;
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| 57 | goto out;
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| 58 | }
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| 59 | get_random_bytes(data, datasize);
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| 60 |
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| 61 | /* Initialize the IV */
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| 62 | get_random_bytes(iv, sizeof(iv));
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| 63 |
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| 64 | /*
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| 65 | * Encrypt the data in-place.
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| 66 | *
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| 67 | * For simplicity, in this example we wait for the request to complete
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| 68 | * before proceeding, even if the underlying implementation is asynchronous.
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| 69 | *
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| 70 | * To decrypt instead of encrypt, just change crypto_skcipher_encrypt() to
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| 71 | * crypto_skcipher_decrypt().
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| 72 | */
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| 73 | sg_init_one(&sg, data, datasize);
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| 74 | skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
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| 75 | CRYPTO_TFM_REQ_MAY_SLEEP,
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| 76 | crypto_req_done, &wait);
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| 77 | skcipher_request_set_crypt(req, &sg, &sg, datasize, iv);
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| 78 | err = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
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| 79 | if (err) {
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| 80 | pr_err("Error encrypting data: %d\n", err);
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| 81 | goto out;
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| 82 | }
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| 83 |
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| 84 | pr_debug("Encryption was successful\n");
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| 85 | out:
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| 86 | crypto_free_skcipher(tfm);
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| 87 | skcipher_request_free(req);
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| 88 | kfree(data);
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| 89 | return err;
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| 90 | }
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| 91 |
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| 92 |
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| 93 | Code Example For Use of Operational State Memory With SHASH
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| 94 | -----------------------------------------------------------
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| 95 |
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| 96 | ::
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| 97 |
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| 98 |
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| 99 | struct sdesc {
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| 100 | struct shash_desc shash;
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| 101 | char ctx[];
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| 102 | };
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| 103 |
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| 104 | static struct sdesc *init_sdesc(struct crypto_shash *alg)
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| 105 | {
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| 106 | struct sdesc *sdesc;
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| 107 | int size;
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| 108 |
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| 109 | size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
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| 110 | sdesc = kmalloc(size, GFP_KERNEL);
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| 111 | if (!sdesc)
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| 112 | return ERR_PTR(-ENOMEM);
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| 113 | sdesc->shash.tfm = alg;
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| 114 | return sdesc;
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| 115 | }
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| 116 |
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| 117 | static int calc_hash(struct crypto_shash *alg,
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| 118 | const unsigned char *data, unsigned int datalen,
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| 119 | unsigned char *digest)
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| 120 | {
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| 121 | struct sdesc *sdesc;
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| 122 | int ret;
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| 123 |
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| 124 | sdesc = init_sdesc(alg);
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| 125 | if (IS_ERR(sdesc)) {
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| 126 | pr_info("can't alloc sdesc\n");
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| 127 | return PTR_ERR(sdesc);
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| 128 | }
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| 129 |
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| 130 | ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest);
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| 131 | kfree(sdesc);
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| 132 | return ret;
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| 133 | }
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| 134 |
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| 135 | static int test_hash(const unsigned char *data, unsigned int datalen,
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| 136 | unsigned char *digest)
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| 137 | {
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| 138 | struct crypto_shash *alg;
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| 139 | char *hash_alg_name = "sha1-padlock-nano";
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| 140 | int ret;
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| 141 |
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| 142 | alg = crypto_alloc_shash(hash_alg_name, 0, 0);
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| 143 | if (IS_ERR(alg)) {
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| 144 | pr_info("can't alloc alg %s\n", hash_alg_name);
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| 145 | return PTR_ERR(alg);
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| 146 | }
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| 147 | ret = calc_hash(alg, data, datalen, digest);
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| 148 | crypto_free_shash(alg);
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| 149 | return ret;
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| 150 | }
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| 151 |
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| 152 |
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| 153 | Code Example For Random Number Generator Usage
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| 154 | ----------------------------------------------
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| 155 |
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| 156 | ::
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| 157 |
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| 158 |
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| 159 | static int get_random_numbers(u8 *buf, unsigned int len)
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| 160 | {
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| 161 | struct crypto_rng *rng = NULL;
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| 162 | char *drbg = "stdrng";
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| 163 | int ret;
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| 164 |
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| 165 | if (!buf || !len) {
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| 166 | pr_debug("No output buffer provided\n");
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| 167 | return -EINVAL;
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| 168 | }
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| 169 |
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| 170 | rng = crypto_alloc_rng(drbg, 0, 0);
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| 171 | if (IS_ERR(rng)) {
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| 172 | pr_debug("could not allocate RNG handle for %s\n", drbg);
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| 173 | return PTR_ERR(rng);
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| 174 | }
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| 175 |
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| 176 | ret = crypto_rng_get_bytes(rng, buf, len);
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| 177 | if (ret < 0)
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| 178 | pr_debug("generation of random numbers failed\n");
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| 179 | else if (ret == 0)
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| 180 | pr_debug("RNG returned no data");
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| 181 | else
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| 182 | pr_debug("RNG returned %d bytes of data\n", ret);
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| 183 |
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| 184 | out:
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| 185 | crypto_free_rng(rng);
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| 186 | return ret;
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| 187 | }
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