e_chacha20poly1305.c revision e9ada863a7b3e81f5d2b1e3bdd2305da902a87f5 
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, aead_chacha20_poly1305_init, 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, aead_chacha20_poly1305_seal, CIPHER_R_TOO_LARGE);
111    return 0;
112  }
113
114  if (in_len + c20_ctx->tag_len < in_len) {
115    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal, 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, aead_chacha20_poly1305_seal,
121                      CIPHER_R_BUFFER_TOO_SMALL);
122    return 0;
123  }
124
125  if (nonce_len != CHACHA20_NONCE_LEN) {
126    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal, CIPHER_R_IV_TOO_LARGE);
127    return 0;
128  }
129
130  memset(poly1305_key, 0, sizeof(poly1305_key));
131  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
132                   c20_ctx->key, nonce, 0);
133
134  CRYPTO_poly1305_init(&poly1305, poly1305_key);
135  poly1305_update_with_length(&poly1305, ad, ad_len);
136  CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
137  poly1305_update_with_length(&poly1305, out, in_len);
138
139  uint8_t tag[POLY1305_TAG_LEN] ALIGNED;
140  CRYPTO_poly1305_finish(&poly1305, tag);
141  memcpy(out + in_len, tag, c20_ctx->tag_len);
142  *out_len = in_len + c20_ctx->tag_len;
143  return 1;
144}
145
146static int aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
147                                       size_t *out_len, size_t max_out_len,
148                                       const uint8_t *nonce, size_t nonce_len,
149                                       const uint8_t *in, size_t in_len,
150                                       const uint8_t *ad, size_t ad_len) {
151  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
152  uint8_t mac[POLY1305_TAG_LEN];
153  uint8_t poly1305_key[32] ALIGNED;
154  size_t plaintext_len;
155  poly1305_state poly1305;
156  const uint64_t in_len_64 = in_len;
157
158  if (in_len < c20_ctx->tag_len) {
159    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_BAD_DECRYPT);
160    return 0;
161  }
162
163  /* The underlying ChaCha implementation may not overflow the block
164   * counter into the second counter word. Therefore we disallow
165   * individual operations that work on more than 256GB at a time.
166   * |in_len_64| is needed because, on 32-bit platforms, size_t is only
167   * 32-bits and this produces a warning because it's always false.
168   * Casting to uint64_t inside the conditional is not sufficient to stop
169   * the warning. */
170  if (in_len_64 >= (1ull << 32) * 64 - 64) {
171    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_TOO_LARGE);
172    return 0;
173  }
174
175  if (nonce_len != CHACHA20_NONCE_LEN) {
176    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_IV_TOO_LARGE);
177    return 0;
178  }
179
180  plaintext_len = in_len - c20_ctx->tag_len;
181
182  if (max_out_len < plaintext_len) {
183    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open,
184                      CIPHER_R_BUFFER_TOO_SMALL);
185    return 0;
186  }
187
188  memset(poly1305_key, 0, sizeof(poly1305_key));
189  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
190                   c20_ctx->key, nonce, 0);
191
192  CRYPTO_poly1305_init(&poly1305, poly1305_key);
193  poly1305_update_with_length(&poly1305, ad, ad_len);
194  poly1305_update_with_length(&poly1305, in, plaintext_len);
195  CRYPTO_poly1305_finish(&poly1305, mac);
196
197  if (CRYPTO_memcmp(mac, in + plaintext_len, c20_ctx->tag_len) != 0) {
198    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_BAD_DECRYPT);
199    return 0;
200  }
201
202  CRYPTO_chacha_20(out, in, plaintext_len, c20_ctx->key, nonce, 1);
203  *out_len = plaintext_len;
204  return 1;
205}
206
207static const EVP_AEAD aead_chacha20_poly1305 = {
208    32,                 /* key len */
209    CHACHA20_NONCE_LEN, /* nonce len */
210    POLY1305_TAG_LEN,   /* overhead */
211    POLY1305_TAG_LEN,   /* max tag length */
212    aead_chacha20_poly1305_init,
213    NULL, /* init_with_direction */
214    aead_chacha20_poly1305_cleanup,
215    aead_chacha20_poly1305_seal,
216    aead_chacha20_poly1305_open,
217    NULL,               /* get_rc4_state */
218};
219
220const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
221  return &aead_chacha20_poly1305;
222}
223