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 <openssl/chacha.h>
18#include <openssl/cipher.h>
19#include <openssl/err.h>
20#include <openssl/mem.h>
21#include <openssl/poly1305.h>
22
23#include "internal.h"
24
25
26#define POLY1305_TAG_LEN 16
27#define CHACHA20_NONCE_LEN 8
28
29struct aead_chacha20_poly1305_ctx {
30  unsigned char key[32];
31  unsigned char tag_len;
32};
33
34static int aead_chacha20_poly1305_init(EVP_AEAD_CTX *ctx, const uint8_t *key,
35                                       size_t key_len, size_t tag_len) {
36  struct aead_chacha20_poly1305_ctx *c20_ctx;
37
38  if (tag_len == 0) {
39    tag_len = POLY1305_TAG_LEN;
40  }
41
42  if (tag_len > POLY1305_TAG_LEN) {
43    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_init, CIPHER_R_TOO_LARGE);
44    return 0;
45  }
46
47  if (key_len != sizeof(c20_ctx->key)) {
48    return 0; /* internal error - EVP_AEAD_CTX_init should catch this. */
49  }
50
51  c20_ctx = OPENSSL_malloc(sizeof(struct aead_chacha20_poly1305_ctx));
52  if (c20_ctx == NULL) {
53    return 0;
54  }
55
56  memcpy(c20_ctx->key, key, key_len);
57  c20_ctx->tag_len = tag_len;
58  ctx->aead_state = c20_ctx;
59
60  return 1;
61}
62
63static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {
64  struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
65  OPENSSL_cleanse(c20_ctx->key, sizeof(c20_ctx->key));
66  OPENSSL_free(c20_ctx);
67}
68
69static void poly1305_update_with_length(poly1305_state *poly1305,
70                                        const uint8_t *data, size_t data_len) {
71  size_t j = data_len;
72  uint8_t length_bytes[8];
73  unsigned i;
74
75  for (i = 0; i < sizeof(length_bytes); i++) {
76    length_bytes[i] = j;
77    j >>= 8;
78  }
79
80  CRYPTO_poly1305_update(poly1305, data, data_len);
81  CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
82}
83
84#if __arm__
85#define ALIGNED __attribute__((aligned(16)))
86#else
87#define ALIGNED
88#endif
89
90static int aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, uint8_t *out,
91                                       size_t *out_len, size_t max_out_len,
92                                       const uint8_t *nonce, size_t nonce_len,
93                                       const uint8_t *in, size_t in_len,
94                                       const uint8_t *ad, size_t ad_len) {
95  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
96  uint8_t poly1305_key[32] ALIGNED;
97  poly1305_state poly1305;
98  const uint64_t in_len_64 = in_len;
99
100  /* The underlying ChaCha implementation may not overflow the block
101   * counter into the second counter word. Therefore we disallow
102   * individual operations that work on more than 256GB at a time.
103   * |in_len_64| is needed because, on 32-bit platforms, size_t is only
104   * 32-bits and this produces a warning because it's always false.
105   * Casting to uint64_t inside the conditional is not sufficient to stop
106   * the warning. */
107  if (in_len_64 >= (1ull << 32) * 64 - 64) {
108    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal, CIPHER_R_TOO_LARGE);
109    return 0;
110  }
111
112  if (in_len + c20_ctx->tag_len < in_len) {
113    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal, CIPHER_R_TOO_LARGE);
114    return 0;
115  }
116
117  if (max_out_len < in_len + c20_ctx->tag_len) {
118    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal,
119                      CIPHER_R_BUFFER_TOO_SMALL);
120    return 0;
121  }
122
123  if (nonce_len != CHACHA20_NONCE_LEN) {
124    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_seal, CIPHER_R_IV_TOO_LARGE);
125    return 0;
126  }
127
128  memset(poly1305_key, 0, sizeof(poly1305_key));
129  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
130                   c20_ctx->key, nonce, 0);
131
132  CRYPTO_poly1305_init(&poly1305, poly1305_key);
133  poly1305_update_with_length(&poly1305, ad, ad_len);
134  CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
135  poly1305_update_with_length(&poly1305, out, in_len);
136
137  if (c20_ctx->tag_len != POLY1305_TAG_LEN) {
138    uint8_t tag[POLY1305_TAG_LEN];
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
145  CRYPTO_poly1305_finish(&poly1305, out + in_len);
146  *out_len = in_len + c20_ctx->tag_len;
147  return 1;
148}
149
150static int aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
151                                       size_t *out_len, size_t max_out_len,
152                                       const uint8_t *nonce, size_t nonce_len,
153                                       const uint8_t *in, size_t in_len,
154                                       const uint8_t *ad, size_t ad_len) {
155  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
156  uint8_t mac[POLY1305_TAG_LEN];
157  uint8_t poly1305_key[32] ALIGNED;
158  size_t plaintext_len;
159  poly1305_state poly1305;
160  const uint64_t in_len_64 = in_len;
161
162  if (in_len < c20_ctx->tag_len) {
163    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_BAD_DECRYPT);
164    return 0;
165  }
166
167  /* The underlying ChaCha implementation may not overflow the block
168   * counter into the second counter word. Therefore we disallow
169   * individual operations that work on more than 256GB at a time.
170   * |in_len_64| is needed because, on 32-bit platforms, size_t is only
171   * 32-bits and this produces a warning because it's always false.
172   * Casting to uint64_t inside the conditional is not sufficient to stop
173   * the warning. */
174  if (in_len_64 >= (1ull << 32) * 64 - 64) {
175    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_TOO_LARGE);
176    return 0;
177  }
178
179  if (nonce_len != CHACHA20_NONCE_LEN) {
180    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_IV_TOO_LARGE);
181    return 0;
182  }
183
184  plaintext_len = in_len - c20_ctx->tag_len;
185
186  if (max_out_len < plaintext_len) {
187    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open,
188                      CIPHER_R_BUFFER_TOO_SMALL);
189    return 0;
190  }
191
192  memset(poly1305_key, 0, sizeof(poly1305_key));
193  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
194                   c20_ctx->key, nonce, 0);
195
196  CRYPTO_poly1305_init(&poly1305, poly1305_key);
197  poly1305_update_with_length(&poly1305, ad, ad_len);
198  poly1305_update_with_length(&poly1305, in, plaintext_len);
199  CRYPTO_poly1305_finish(&poly1305, mac);
200
201  if (CRYPTO_memcmp(mac, in + plaintext_len, c20_ctx->tag_len) != 0) {
202    OPENSSL_PUT_ERROR(CIPHER, aead_chacha20_poly1305_open, CIPHER_R_BAD_DECRYPT);
203    return 0;
204  }
205
206  CRYPTO_chacha_20(out, in, plaintext_len, c20_ctx->key, nonce, 1);
207  *out_len = plaintext_len;
208  return 1;
209}
210
211static const EVP_AEAD aead_chacha20_poly1305 = {
212    32,                 /* key len */
213    CHACHA20_NONCE_LEN, /* nonce len */
214    POLY1305_TAG_LEN,   /* overhead */
215    POLY1305_TAG_LEN,   /* max tag length */
216    aead_chacha20_poly1305_init, aead_chacha20_poly1305_cleanup,
217    aead_chacha20_poly1305_seal, aead_chacha20_poly1305_open,
218};
219
220const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
221  return &aead_chacha20_poly1305;
222}
223