1 Code Examples
2 =============
3
4 Code Example For Symmetric Key Cipher Operation
5 -----------------------------------------------
6
7 This code encrypts some data with AES-256-XTS. For sake of example,
8 all inputs are random bytes, the encryption is done in-place, and it's
9 assumed the code is running in a context where it can sleep.
10
11 ::
12
13 static int test_skcipher(void)
14 {
15 struct crypto_skcipher *tfm = NULL;
16 struct skcipher_request *req = NULL;
17 u8 *data = NULL;
18 const size_t datasize = 512; /* data size in bytes */
19 struct scatterlist sg;
20 DECLARE_CRYPTO_WAIT(wait);
21 u8 iv[16]; /* AES-256-XTS takes a 16-byte IV */
22 u8 key[64]; /* AES-256-XTS takes a 64-byte key */
23 int err;
24
25 /*
26 * Allocate a tfm (a transformation object) and set the key.
27 *
28 * In real-world use, a tfm and key are typically used for many
29 * encryption/decryption operations. But in this example, we'll just do a
30 * single encryption operation with it (which is not very efficient).
31 */
32
33 tfm = crypto_alloc_skcipher("xts(aes)", 0, 0);
34 if (IS_ERR(tfm)) {
35 pr_err("Error allocating xts(aes) handle: %ld\n", PTR_ERR(tfm));
36 return PTR_ERR(tfm);
37 }
38
39 get_random_bytes(key, sizeof(key));
40 err = crypto_skcipher_setkey(tfm, key, sizeof(key));
41 if (err) {
42 pr_err("Error setting key: %d\n", err);
43 goto out;
44 }
45
46 /* Allocate a request object */
47 req = skcipher_request_alloc(tfm, GFP_KERNEL);
48 if (!req) {
49 err = -ENOMEM;
50 goto out;
51 }
52
53 /* Prepare the input data */
54 data = kmalloc(datasize, GFP_KERNEL);
55 if (!data) {
56 err = -ENOMEM;
57 goto out;
58 }
59 get_random_bytes(data, datasize);
60
61 /* Initialize the IV */
62 get_random_bytes(iv, sizeof(iv));
63
64 /*
65 * Encrypt the data in-place.
66 *
67 * For simplicity, in this example we wait for the request to complete
68 * before proceeding, even if the underlying implementation is asynchronous.
69 *
70 * To decrypt instead of encrypt, just change crypto_skcipher_encrypt() to
71 * crypto_skcipher_decrypt().
72 */
73 sg_init_one(&sg, data, datasize);
74 skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
75 CRYPTO_TFM_REQ_MAY_SLEEP,
76 crypto_req_done, &wait);
77 skcipher_request_set_crypt(req, &sg, &sg, datasize, iv);
78 err = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
79 if (err) {
80 pr_err("Error encrypting data: %d\n", err);
81 goto out;
82 }
83
84 pr_debug("Encryption was successful\n");
85 out:
86 crypto_free_skcipher(tfm);
87 skcipher_request_free(req);
88 kfree(data);
89 return err;
90 }
91
92
93 Code Example For Use of Operational State Memory With SHASH
94 -----------------------------------------------------------
95
96 ::
97
98
99 struct sdesc {
100 struct shash_desc shash;
101 char ctx[];
102 };
103
104 static struct sdesc *init_sdesc(struct crypto_shash *alg)
105 {
106 struct sdesc *sdesc;
107 int size;
108
109 size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
110 sdesc = kmalloc(size, GFP_KERNEL);
111 if (!sdesc)
112 return ERR_PTR(-ENOMEM);
113 sdesc->shash.tfm = alg;
114 return sdesc;
115 }
116
117 static int calc_hash(struct crypto_shash *alg,
118 const unsigned char *data, unsigned int datalen,
119 unsigned char *digest)
120 {
121 struct sdesc *sdesc;
122 int ret;
123
124 sdesc = init_sdesc(alg);
125 if (IS_ERR(sdesc)) {
126 pr_info("can't alloc sdesc\n");
127 return PTR_ERR(sdesc);
128 }
129
130 ret = crypto_shash_digest(&sdesc->shash, data, datalen, digest);
131 kfree(sdesc);
132 return ret;
133 }
134
135 static int test_hash(const unsigned char *data, unsigned int datalen,
136 unsigned char *digest)
137 {
138 struct crypto_shash *alg;
139 char *hash_alg_name = "sha1-padlock-nano";
140 int ret;
141
142 alg = crypto_alloc_shash(hash_alg_name, 0, 0);
143 if (IS_ERR(alg)) {
144 pr_info("can't alloc alg %s\n", hash_alg_name);
145 return PTR_ERR(alg);
146 }
147 ret = calc_hash(alg, data, datalen, digest);
148 crypto_free_shash(alg);
149 return ret;
150 }
151
152
153 Code Example For Random Number Generator Usage
154 ----------------------------------------------
155
156 ::
157
158
159 static int get_random_numbers(u8 *buf, unsigned int len)
160 {
161 struct crypto_rng *rng = NULL;
162 char *drbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */
163 int ret;
164
165 if (!buf || !len) {
166 pr_debug("No output buffer provided\n");
167 return -EINVAL;
168 }
169
170 rng = crypto_alloc_rng(drbg, 0, 0);
171 if (IS_ERR(rng)) {
172 pr_debug("could not allocate RNG handle for %s\n", drbg);
173 return PTR_ERR(rng);
174 }
175
176 ret = crypto_rng_get_bytes(rng, buf, len);
177 if (ret < 0)
178 pr_debug("generation of random numbers failed\n");
179 else if (ret == 0)
180 pr_debug("RNG returned no data");
181 else
182 pr_debug("RNG returned %d bytes of data\n", ret);
183
184 out:
185 crypto_free_rng(rng);
186 return ret;
187 }
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