1 /*
2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /*
28 * Implementation Notes
29 * ====================
30 *
31 * Since CTR and GHASH implementations can handle only full blocks, a
32 * 16-byte buffer (buf[]) is maintained in the context:
33 *
34 * - When processing AAD, buf[] contains the 0-15 unprocessed bytes.
35 *
36 * - When doing CTR encryption / decryption, buf[] contains the AES output
37 * for the last partial block, to be used with the next few bytes of
38 * data, as well as the already encrypted bytes. For instance, if the
39 * processed data length so far is 21 bytes, then buf[0..4] contains
40 * the five last encrypted bytes, and buf[5..15] contains the next 11
41 * AES output bytes to be XORed with the next 11 bytes of input.
42 *
43 * The recorded AES output bytes are used to complete the block when
44 * the corresponding bytes are obtained. Note that buf[] always
45 * contains the _encrypted_ bytes, whether we apply encryption or
46 * decryption: these bytes are used as input to GHASH when the block
47 * is complete.
48 *
49 * In both cases, the low bits of the data length counters (count_aad,
50 * count_ctr) are used to work out the current situation.
51 */
52
53 /* see bearssl_aead.h */
54 void
br_gcm_init(br_gcm_context * ctx,const br_block_ctr_class ** bctx,br_ghash gh)55 br_gcm_init(br_gcm_context *ctx, const br_block_ctr_class **bctx, br_ghash gh)
56 {
57 unsigned char iv[12];
58
59 ctx->vtable = &br_gcm_vtable;
60 ctx->bctx = bctx;
61 ctx->gh = gh;
62
63 /*
64 * The GHASH key h[] is the raw encryption of the all-zero
65 * block. Since we only have a CTR implementation, we use it
66 * with an all-zero IV and a zero counter, to CTR-encrypt an
67 * all-zero block.
68 */
69 memset(ctx->h, 0, sizeof ctx->h);
70 memset(iv, 0, sizeof iv);
71 (*bctx)->run(bctx, iv, 0, ctx->h, sizeof ctx->h);
72 }
73
74 /* see bearssl_aead.h */
75 void
br_gcm_reset(br_gcm_context * ctx,const void * iv,size_t len)76 br_gcm_reset(br_gcm_context *ctx, const void *iv, size_t len)
77 {
78 /*
79 * If the provided nonce is 12 bytes, then this is the initial
80 * IV for CTR mode; it will be used with a counter that starts
81 * at 2 (value 1 is for encrypting the GHASH output into the tag).
82 *
83 * If the provided nonce has any other length, then it is hashed
84 * (with GHASH) into a 16-byte value that will be the IV for CTR
85 * (both 12-byte IV and 32-bit counter).
86 */
87 if (len == 12) {
88 memcpy(ctx->j0_1, iv, 12);
89 ctx->j0_2 = 1;
90 } else {
91 unsigned char ty[16], tmp[16];
92
93 memset(ty, 0, sizeof ty);
94 ctx->gh(ty, ctx->h, iv, len);
95 memset(tmp, 0, 8);
96 br_enc64be(tmp + 8, (uint64_t)len << 3);
97 ctx->gh(ty, ctx->h, tmp, 16);
98 memcpy(ctx->j0_1, ty, 12);
99 ctx->j0_2 = br_dec32be(ty + 12);
100 }
101 ctx->jc = ctx->j0_2 + 1;
102 memset(ctx->y, 0, sizeof ctx->y);
103 ctx->count_aad = 0;
104 ctx->count_ctr = 0;
105 }
106
107 /* see bearssl_aead.h */
108 void
br_gcm_aad_inject(br_gcm_context * ctx,const void * data,size_t len)109 br_gcm_aad_inject(br_gcm_context *ctx, const void *data, size_t len)
110 {
111 size_t ptr, dlen;
112
113 ptr = (size_t)ctx->count_aad & (size_t)15;
114 if (ptr != 0) {
115 /*
116 * If there is a partial block, then we first try to
117 * complete it.
118 */
119 size_t clen;
120
121 clen = 16 - ptr;
122 if (len < clen) {
123 memcpy(ctx->buf + ptr, data, len);
124 ctx->count_aad += (uint64_t)len;
125 return;
126 }
127 memcpy(ctx->buf + ptr, data, clen);
128 ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
129 data = (const unsigned char *)data + clen;
130 len -= clen;
131 ctx->count_aad += (uint64_t)clen;
132 }
133
134 /*
135 * Now AAD is aligned on a 16-byte block (with regards to GHASH).
136 * We process all complete blocks, and save the last partial
137 * block.
138 */
139 dlen = len & ~(size_t)15;
140 ctx->gh(ctx->y, ctx->h, data, dlen);
141 memcpy(ctx->buf, (const unsigned char *)data + dlen, len - dlen);
142 ctx->count_aad += (uint64_t)len;
143 }
144
145 /* see bearssl_aead.h */
146 void
br_gcm_flip(br_gcm_context * ctx)147 br_gcm_flip(br_gcm_context *ctx)
148 {
149 /*
150 * We complete the GHASH computation if there is a partial block.
151 * The GHASH implementation automatically applies padding with
152 * zeros.
153 */
154 size_t ptr;
155
156 ptr = (size_t)ctx->count_aad & (size_t)15;
157 if (ptr != 0) {
158 ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
159 }
160 }
161
162 /* see bearssl_aead.h */
163 void
br_gcm_run(br_gcm_context * ctx,int encrypt,void * data,size_t len)164 br_gcm_run(br_gcm_context *ctx, int encrypt, void *data, size_t len)
165 {
166 unsigned char *buf;
167 size_t ptr, dlen;
168
169 buf = data;
170 ptr = (size_t)ctx->count_ctr & (size_t)15;
171 if (ptr != 0) {
172 /*
173 * If we have a partial block, then we try to complete it.
174 */
175 size_t u, clen;
176
177 clen = 16 - ptr;
178 if (len < clen) {
179 clen = len;
180 }
181 for (u = 0; u < clen; u ++) {
182 unsigned x, y;
183
184 x = buf[u];
185 y = x ^ ctx->buf[ptr + u];
186 ctx->buf[ptr + u] = encrypt ? y : x;
187 buf[u] = y;
188 }
189 ctx->count_ctr += (uint64_t)clen;
190 buf += clen;
191 len -= clen;
192 if (ptr + clen < 16) {
193 return;
194 }
195 ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
196 }
197
198 /*
199 * Process full blocks.
200 */
201 dlen = len & ~(size_t)15;
202 if (!encrypt) {
203 ctx->gh(ctx->y, ctx->h, buf, dlen);
204 }
205 ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->jc, buf, dlen);
206 if (encrypt) {
207 ctx->gh(ctx->y, ctx->h, buf, dlen);
208 }
209 buf += dlen;
210 len -= dlen;
211 ctx->count_ctr += (uint64_t)dlen;
212
213 if (len > 0) {
214 /*
215 * There is a partial block.
216 */
217 size_t u;
218
219 memset(ctx->buf, 0, sizeof ctx->buf);
220 ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1,
221 ctx->jc, ctx->buf, 16);
222 for (u = 0; u < len; u ++) {
223 unsigned x, y;
224
225 x = buf[u];
226 y = x ^ ctx->buf[u];
227 ctx->buf[u] = encrypt ? y : x;
228 buf[u] = y;
229 }
230 ctx->count_ctr += (uint64_t)len;
231 }
232 }
233
234 /* see bearssl_aead.h */
235 void
br_gcm_get_tag(br_gcm_context * ctx,void * tag)236 br_gcm_get_tag(br_gcm_context *ctx, void *tag)
237 {
238 size_t ptr;
239 unsigned char tmp[16];
240
241 ptr = (size_t)ctx->count_ctr & (size_t)15;
242 if (ptr > 0) {
243 /*
244 * There is a partial block: encrypted/decrypted data has
245 * been produced, but the encrypted bytes must still be
246 * processed by GHASH.
247 */
248 ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
249 }
250
251 /*
252 * Final block for GHASH: the AAD and plaintext lengths (in bits).
253 */
254 br_enc64be(tmp, ctx->count_aad << 3);
255 br_enc64be(tmp + 8, ctx->count_ctr << 3);
256 ctx->gh(ctx->y, ctx->h, tmp, 16);
257
258 /*
259 * Tag is the GHASH output XORed with the encryption of the
260 * nonce with the initial counter value.
261 */
262 memcpy(tag, ctx->y, 16);
263 (*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->j0_2, tag, 16);
264 }
265
266 /* see bearssl_aead.h */
267 void
br_gcm_get_tag_trunc(br_gcm_context * ctx,void * tag,size_t len)268 br_gcm_get_tag_trunc(br_gcm_context *ctx, void *tag, size_t len)
269 {
270 unsigned char tmp[16];
271
272 br_gcm_get_tag(ctx, tmp);
273 memcpy(tag, tmp, len);
274 }
275
276 /* see bearssl_aead.h */
277 uint32_t
br_gcm_check_tag_trunc(br_gcm_context * ctx,const void * tag,size_t len)278 br_gcm_check_tag_trunc(br_gcm_context *ctx, const void *tag, size_t len)
279 {
280 unsigned char tmp[16];
281 size_t u;
282 int x;
283
284 br_gcm_get_tag(ctx, tmp);
285 x = 0;
286 for (u = 0; u < len; u ++) {
287 x |= tmp[u] ^ ((const unsigned char *)tag)[u];
288 }
289 return EQ0(x);
290 }
291
292 /* see bearssl_aead.h */
293 uint32_t
br_gcm_check_tag(br_gcm_context * ctx,const void * tag)294 br_gcm_check_tag(br_gcm_context *ctx, const void *tag)
295 {
296 return br_gcm_check_tag_trunc(ctx, tag, 16);
297 }
298
299 /* see bearssl_aead.h */
300 const br_aead_class br_gcm_vtable = {
301 16,
302 (void (*)(const br_aead_class **, const void *, size_t))
303 &br_gcm_reset,
304 (void (*)(const br_aead_class **, const void *, size_t))
305 &br_gcm_aad_inject,
306 (void (*)(const br_aead_class **))
307 &br_gcm_flip,
308 (void (*)(const br_aead_class **, int, void *, size_t))
309 &br_gcm_run,
310 (void (*)(const br_aead_class **, void *))
311 &br_gcm_get_tag,
312 (uint32_t (*)(const br_aead_class **, const void *))
313 &br_gcm_check_tag,
314 (void (*)(const br_aead_class **, void *, size_t))
315 &br_gcm_get_tag_trunc,
316 (uint32_t (*)(const br_aead_class **, const void *, size_t))
317 &br_gcm_check_tag_trunc
318 };
319