e_chacha20poly1305.c revision 1e4884f615b20946411a74e41eb9c6aa65e2d5f3 
1/* Copyright (c) 2014, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15#include <openssl/aead.h>
16
17#include <string.h>
18
19#include <openssl/chacha.h>
20#include <openssl/cipher.h>
21#include <openssl/err.h>
22#include <openssl/mem.h>
23#include <openssl/poly1305.h>
24
25#include "internal.h"
26
27
28#define POLY1305_TAG_LEN 16
29#define CHACHA20_NONCE_LEN 8
30
31struct aead_chacha20_poly1305_ctx {
32  unsigned char key[32];
33  unsigned char tag_len;
34};
35
36static int aead_chacha20_poly1305_init(EVP_AEAD_CTX *ctx, const uint8_t *key,
37                                       size_t key_len, size_t tag_len) {
38  struct aead_chacha20_poly1305_ctx *c20_ctx;
39
40  if (tag_len == 0) {
41    tag_len = POLY1305_TAG_LEN;
42  }
43
44  if (tag_len > POLY1305_TAG_LEN) {
45    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
46    return 0;
47  }
48
49  if (key_len != sizeof(c20_ctx->key)) {
50    return 0; /* internal error - EVP_AEAD_CTX_init should catch this. */
51  }
52
53  c20_ctx = OPENSSL_malloc(sizeof(struct aead_chacha20_poly1305_ctx));
54  if (c20_ctx == NULL) {
55    return 0;
56  }
57
58  memcpy(c20_ctx->key, key, key_len);
59  c20_ctx->tag_len = tag_len;
60  ctx->aead_state = c20_ctx;
61
62  return 1;
63}
64
65static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {
66  struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
67  OPENSSL_cleanse(c20_ctx->key, sizeof(c20_ctx->key));
68  OPENSSL_free(c20_ctx);
69}
70
71static void poly1305_update_with_length(poly1305_state *poly1305,
72                                        const uint8_t *data, size_t data_len) {
73  size_t j = data_len;
74  uint8_t length_bytes[8];
75  unsigned i;
76
77  for (i = 0; i < sizeof(length_bytes); i++) {
78    length_bytes[i] = j;
79    j >>= 8;
80  }
81
82  CRYPTO_poly1305_update(poly1305, data, data_len);
83  CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
84}
85
86#if defined(__arm__)
87#define ALIGNED __attribute__((aligned(16)))
88#else
89#define ALIGNED
90#endif
91
92static int aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, uint8_t *out,
93                                       size_t *out_len, size_t max_out_len,
94                                       const uint8_t *nonce, size_t nonce_len,
95                                       const uint8_t *in, size_t in_len,
96                                       const uint8_t *ad, size_t ad_len) {
97  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
98  uint8_t poly1305_key[32] ALIGNED;
99  poly1305_state poly1305;
100  const uint64_t in_len_64 = in_len;
101
102  /* The underlying ChaCha implementation may not overflow the block
103   * counter into the second counter word. Therefore we disallow
104   * individual operations that work on more than 256GB at a time.
105   * |in_len_64| is needed because, on 32-bit platforms, size_t is only
106   * 32-bits and this produces a warning because it's always false.
107   * Casting to uint64_t inside the conditional is not sufficient to stop
108   * the warning. */
109  if (in_len_64 >= (1ull << 32) * 64 - 64) {
110    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
111    return 0;
112  }
113
114  if (in_len + c20_ctx->tag_len < in_len) {
115    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
116    return 0;
117  }
118
119  if (max_out_len < in_len + c20_ctx->tag_len) {
120    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
121    return 0;
122  }
123
124  if (nonce_len != CHACHA20_NONCE_LEN) {
125    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_IV_TOO_LARGE);
126    return 0;
127  }
128
129  memset(poly1305_key, 0, sizeof(poly1305_key));
130  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
131                   c20_ctx->key, nonce, 0);
132
133  CRYPTO_poly1305_init(&poly1305, poly1305_key);
134  poly1305_update_with_length(&poly1305, ad, ad_len);
135  CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
136  poly1305_update_with_length(&poly1305, out, in_len);
137
138  uint8_t tag[POLY1305_TAG_LEN] ALIGNED;
139  CRYPTO_poly1305_finish(&poly1305, tag);
140  memcpy(out + in_len, tag, c20_ctx->tag_len);
141  *out_len = in_len + c20_ctx->tag_len;
142  return 1;
143}
144
145static int aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
146                                       size_t *out_len, size_t max_out_len,
147                                       const uint8_t *nonce, size_t nonce_len,
148                                       const uint8_t *in, size_t in_len,
149                                       const uint8_t *ad, size_t ad_len) {
150  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
151  uint8_t mac[POLY1305_TAG_LEN];
152  uint8_t poly1305_key[32] ALIGNED;
153  size_t plaintext_len;
154  poly1305_state poly1305;
155  const uint64_t in_len_64 = in_len;
156
157  if (in_len < c20_ctx->tag_len) {
158    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
159    return 0;
160  }
161
162  /* The underlying ChaCha implementation may not overflow the block
163   * counter into the second counter word. Therefore we disallow
164   * individual operations that work on more than 256GB at a time.
165   * |in_len_64| is needed because, on 32-bit platforms, size_t is only
166   * 32-bits and this produces a warning because it's always false.
167   * Casting to uint64_t inside the conditional is not sufficient to stop
168   * the warning. */
169  if (in_len_64 >= (1ull << 32) * 64 - 64) {
170    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
171    return 0;
172  }
173
174  if (nonce_len != CHACHA20_NONCE_LEN) {
175    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_IV_TOO_LARGE);
176    return 0;
177  }
178
179  plaintext_len = in_len - c20_ctx->tag_len;
180
181  if (max_out_len < plaintext_len) {
182    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
183    return 0;
184  }
185
186  memset(poly1305_key, 0, sizeof(poly1305_key));
187  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
188                   c20_ctx->key, nonce, 0);
189
190  CRYPTO_poly1305_init(&poly1305, poly1305_key);
191  poly1305_update_with_length(&poly1305, ad, ad_len);
192  poly1305_update_with_length(&poly1305, in, plaintext_len);
193  CRYPTO_poly1305_finish(&poly1305, mac);
194
195  if (CRYPTO_memcmp(mac, in + plaintext_len, c20_ctx->tag_len) != 0) {
196    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
197    return 0;
198  }
199
200  CRYPTO_chacha_20(out, in, plaintext_len, c20_ctx->key, nonce, 1);
201  *out_len = plaintext_len;
202  return 1;
203}
204
205static const EVP_AEAD aead_chacha20_poly1305 = {
206    32,                 /* key len */
207    CHACHA20_NONCE_LEN, /* nonce len */
208    POLY1305_TAG_LEN,   /* overhead */
209    POLY1305_TAG_LEN,   /* max tag length */
210    aead_chacha20_poly1305_init,
211    NULL, /* init_with_direction */
212    aead_chacha20_poly1305_cleanup,
213    aead_chacha20_poly1305_seal,
214    aead_chacha20_poly1305_open,
215    NULL,               /* get_rc4_state */
216};
217
218const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
219  return &aead_chacha20_poly1305;
220}
221