| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * The GCM authenticated encryption mode |
| 4 | * |
| 5 | * (c) 2018 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of Catacomb. |
| 11 | * |
| 12 | * Catacomb is free software: you can redistribute it and/or modify it |
| 13 | * under the terms of the GNU Library General Public License as published |
| 14 | * by the Free Software Foundation; either version 2 of the License, or |
| 15 | * (at your option) any later version. |
| 16 | * |
| 17 | * Catacomb is distributed in the hope that it will be useful, but |
| 18 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 20 | * Library General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU Library General Public |
| 23 | * License along with Catacomb. If not, write to the Free Software |
| 24 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, |
| 25 | * USA. |
| 26 | */ |
| 27 | |
| 28 | /*----- Notes on GCM ------------------------------------------------------* |
| 29 | * |
| 30 | * The name is short for `Galois Counter Mode'. GCM was designed in 2005 by |
| 31 | * David McGrew and John Viega as a fast, patent-free authenticated |
| 32 | * encryption scheme; and it's specified by NIST in SP800-38D. It combines |
| 33 | * counter-mode encryption with a Carter--Wegman authenticator based on a |
| 34 | * polynomial hash over %$\gf{2^{128}}%, so it needs only one blockcipher |
| 35 | * application per message block, together with a multiplication by a |
| 36 | * constant in the finite field. GCM is essentially the winner in the |
| 37 | * authenticated-encryption-mode competition, to the extent that Intel and |
| 38 | * ARM both added instructions to their architectures to accelerate it. |
| 39 | * |
| 40 | * GCM allows arbitrary-sized nonces, though it's happiest if the nonce is 32 |
| 41 | * bits shorter than the block size, leaving a fixed-size block counter in |
| 42 | * the low 32 bits. It permits header data to be processed independently of |
| 43 | * the message, though doing this requires some slightly fiddly algebra and |
| 44 | * most implementations don't allow callers to take advantage of this. |
| 45 | * |
| 46 | * One downside is that the field multiplication is inefficient in software. |
| 47 | * Back in 2005 it was assumed that implementors would use large tables, but |
| 48 | * that leaks the authentication secret through the processor cache. This |
| 49 | * implementation runs in constant time, but the penalty is that, without |
| 50 | * dedicated processor support, it's much slower than an extra blockcipher |
| 51 | * application would have been. |
| 52 | * |
| 53 | * Another downside is that, while GCM came with a security proof, it was |
| 54 | * subtly incorrect in a few ways which mean that its concrete security is |
| 55 | * significantly less than one would expect. |
| 56 | * |
| 57 | * If interoperability isn't a concern, then OCB3 is probably a better |
| 58 | * choice; if the OCB patent situation is also worrying, then EAX is likely |
| 59 | * preferable. |
| 60 | */ |
| 61 | |
| 62 | #ifndef CATACOMB_GCM_H |
| 63 | #define CATACOMB_GCM_H |
| 64 | |
| 65 | #ifdef __cplusplus |
| 66 | extern "C" { |
| 67 | #endif |
| 68 | |
| 69 | /*----- Header files ------------------------------------------------------*/ |
| 70 | |
| 71 | #include <stddef.h> |
| 72 | |
| 73 | #include <mLib/bits.h> |
| 74 | #include <mLib/buf.h> |
| 75 | |
| 76 | #ifndef CATACOMB_GAEAD_H |
| 77 | # include "gaead.h" |
| 78 | #endif |
| 79 | |
| 80 | /*----- Macros ------------------------------------------------------------*/ |
| 81 | |
| 82 | /* --- @GCM_DECL@ --- * |
| 83 | * |
| 84 | * Arguments: @PRE@, @pre@ = prefixes for the underlying block cipher |
| 85 | * |
| 86 | * Use: Creates declarations for GCM authenticated-encryption mode. |
| 87 | */ |
| 88 | |
| 89 | #define GCM_DECL(PRE, pre) \ |
| 90 | \ |
| 91 | typedef struct pre##_gcmkey { \ |
| 92 | pre##_ctx ctx; /* Block cipher key */ \ |
| 93 | uint32 ktab[32*PRE##_BLKSZ*PRE##_BLKSZ]; /* Multiplication table */ \ |
| 94 | } pre##_gcmkey; \ |
| 95 | \ |
| 96 | typedef struct pre##_gcmaadctx { \ |
| 97 | pre##_gcmkey k; /* Underlying key */ \ |
| 98 | uint32 a[PRE##_BLKSZ/4]; /* GHASH accumulator */ \ |
| 99 | octet b[PRE##_BLKSZ]; /* Input buffer */ \ |
| 100 | unsigned off; /* Length of stuff in buffer */ \ |
| 101 | unsigned long len; /* Number of blocks so far */ \ |
| 102 | } pre##_gcmaadctx; \ |
| 103 | \ |
| 104 | typedef struct pre##_gcmctx { \ |
| 105 | /* The buffer is split into two portions. The first N octets hold a \ |
| 106 | * chunk of ciphertext, which will be fed into the OMAC calculation; \ |
| 107 | * the remaining BLKSZ - N octets hold E_K(C), which is the XOR mask \ |
| 108 | * to apply to the plaintext or ciphertext. \ |
| 109 | */ \ |
| 110 | pre##_gcmkey k; /* Underlying key */ \ |
| 111 | uint32 c[PRE##_BLKSZ/4]; /* Current counter value */ \ |
| 112 | uint32 c0[PRE##_BLKSZ/4]; /* Initial counter */ \ |
| 113 | uint32 a[PRE##_BLKSZ]; /* GHASH accumulator */ \ |
| 114 | octet b[PRE##_BLKSZ]; /* Ciphertext/mask buffer */ \ |
| 115 | unsigned off; /* Crossover point in buffer */ \ |
| 116 | unsigned long len; /* Number of blocks so far */ \ |
| 117 | } pre##_gcmctx; \ |
| 118 | \ |
| 119 | extern const octet pre##_gcmnoncesz[], pre##_gcmtagsz[]; \ |
| 120 | \ |
| 121 | /* --- @pre_gcmsetkey@ --- * \ |
| 122 | * \ |
| 123 | * Arguments: @pre_gcmkey *key@ = pointer to key block to fill in \ |
| 124 | * @const void *k@ = pointer to key material \ |
| 125 | * @size_t ksz@ = size of key material \ |
| 126 | * \ |
| 127 | * Returns: --- \ |
| 128 | * \ |
| 129 | * Use: Initializes an GCM key block. \ |
| 130 | */ \ |
| 131 | \ |
| 132 | extern void pre##_gcmsetkey(pre##_gcmkey */*key*/, \ |
| 133 | const void */*k*/, size_t /*ksz*/); \ |
| 134 | \ |
| 135 | /* --- @pre_gcmaadinit@ --- * \ |
| 136 | * \ |
| 137 | * Arguments: @pre_gcmaadctx *aad@ = pointer to AAD context \ |
| 138 | * @const pre_gcmkey *key@ = pointer to key block \ |
| 139 | * \ |
| 140 | * Returns: --- \ |
| 141 | * \ |
| 142 | * Use: Initializes an GCM AAD (`additional authenticated \ |
| 143 | * data') context associated with a given key. AAD \ |
| 144 | * contexts can be copied and/or reused, saving time if \ |
| 145 | * the AAD for a number of messages has a common prefix. \ |
| 146 | * \ |
| 147 | * The @key@ doesn't need to be kept around, though \ |
| 148 | * usually there'll at least be another copy in some GCM \ |
| 149 | * operation context because the AAD on its own isn't much \ |
| 150 | * good. \ |
| 151 | */ \ |
| 152 | \ |
| 153 | extern void pre##_gcmaadinit(pre##_gcmaadctx */*aad*/, \ |
| 154 | const pre##_gcmkey */*key*/); \ |
| 155 | \ |
| 156 | /* --- @pre_gcmaadhash@ --- * \ |
| 157 | * \ |
| 158 | * Arguments: @pre_gcmaadctx *aad@ = pointer to AAD context \ |
| 159 | * @const void *p@ = pointer to AAD material \ |
| 160 | * @size_t sz@ = length of AAD material \ |
| 161 | * \ |
| 162 | * Returns: --- \ |
| 163 | * \ |
| 164 | * Use: Feeds AAD into the context. \ |
| 165 | */ \ |
| 166 | \ |
| 167 | extern void pre##_gcmaadhash(pre##_gcmaadctx */*aad*/, \ |
| 168 | const void */*p*/, size_t /*sz*/); \ |
| 169 | \ |
| 170 | /* --- @pre_gcminit@ --- * \ |
| 171 | * \ |
| 172 | * Arguments: @pre_gcmctx *ctx@ = pointer to GCM context \ |
| 173 | * @const pre_gcmkey *key@ = pointer to key block \ |
| 174 | * @const void *n@ = pointer to nonce \ |
| 175 | * @size_t nsz@ = size of nonce \ |
| 176 | * \ |
| 177 | * Returns: --- \ |
| 178 | * \ |
| 179 | * Use: Initialize an GCM operation context with a given key. \ |
| 180 | * \ |
| 181 | * The original key needn't be kept around any more. \ |
| 182 | */ \ |
| 183 | \ |
| 184 | extern void pre##_gcminit(pre##_gcmctx */*ctx*/, \ |
| 185 | const pre##_gcmkey */*k*/, \ |
| 186 | const void */*n*/, size_t /*nsz*/); \ |
| 187 | \ |
| 188 | /* --- @pre_gcmreinit@ --- * \ |
| 189 | * \ |
| 190 | * Arguments: @pre_gcmctx *ctx@ = pointer to GCM context \ |
| 191 | * @const void *n@ = pointer to nonce \ |
| 192 | * @size_t nsz@ = size of nonce \ |
| 193 | * \ |
| 194 | * Returns: --- \ |
| 195 | * \ |
| 196 | * Use: Reinitialize an GCM operation context, changing the \ |
| 197 | * nonce. \ |
| 198 | */ \ |
| 199 | \ |
| 200 | extern void pre##_gcmreinit(pre##_gcmctx */*ctx*/, \ |
| 201 | const void */*n*/, size_t /*nsz*/); \ |
| 202 | \ |
| 203 | /* --- @pre_gcmencrypt@ --- * \ |
| 204 | * \ |
| 205 | * Arguments: @pre_gcmctx *ctx@ = pointer to GCM operation context \ |
| 206 | * @const void *src@ = pointer to plaintext message chunk \ |
| 207 | * @size_t sz@ = size of the plaintext \ |
| 208 | * @buf *dst@ = a buffer to write the ciphertext to \ |
| 209 | * \ |
| 210 | * Returns: Zero on success; @-1@ on failure. \ |
| 211 | * \ |
| 212 | * Use: Encrypts a chunk of a plaintext message, writing a \ |
| 213 | * chunk of ciphertext to the output buffer and updating \ |
| 214 | * the operation state. \ |
| 215 | * \ |
| 216 | * For GCM, we always write a ciphertext chunk the same \ |
| 217 | * size as the plaintext. The messing about with @buf@ \ |
| 218 | * objects makes the interface consistent with other AEAD \ |
| 219 | * schemes which can't do this. \ |
| 220 | */ \ |
| 221 | \ |
| 222 | extern int pre##_gcmencrypt(pre##_gcmctx */*ctx*/, \ |
| 223 | const void */*src*/, size_t /*sz*/, \ |
| 224 | buf */*dst*/); \ |
| 225 | \ |
| 226 | /* --- @pre_gcmdecrypt@ --- * \ |
| 227 | * \ |
| 228 | * Arguments: @pre_gcmctx *ctx@ = pointer to GCM operation context \ |
| 229 | * @const void *src@ = pointer to ciphertext message chunk \ |
| 230 | * @size_t sz@ = size of the ciphertext \ |
| 231 | * @buf *dst@ = a buffer to write the plaintext to \ |
| 232 | * \ |
| 233 | * Returns: Zero on success; @-1@ on failure. \ |
| 234 | * \ |
| 235 | * Use: Decrypts a chunk of a ciphertext message, writing a \ |
| 236 | * chunk of plaintext to the output buffer and updating \ |
| 237 | * the operation state. \ |
| 238 | * \ |
| 239 | * For GCM, we always write a plaintext chunk the same \ |
| 240 | * size as the ciphertext. The messing about with @buf@ \ |
| 241 | * objects makes the interface consistent with other AEAD \ |
| 242 | * schemes which can't do this. \ |
| 243 | */ \ |
| 244 | \ |
| 245 | extern int pre##_gcmdecrypt(pre##_gcmctx */*ctx*/, \ |
| 246 | const void */*src*/, size_t /*sz*/, \ |
| 247 | buf */*dst*/); \ |
| 248 | \ |
| 249 | /* --- @pre_gcmencryptdone@ --- * \ |
| 250 | * \ |
| 251 | * Arguments: @pre_gcmctx *ctx@ = pointer to an GCM context \ |
| 252 | * @const pre_gcmaadctx *aad@ = pointer to AAD context, or \ |
| 253 | * null \ |
| 254 | * @buf *dst@ = buffer for remaining ciphertext \ |
| 255 | * @void *tag@ = where to write the tag \ |
| 256 | * @size_t tsz@ = length of tag to store \ |
| 257 | * \ |
| 258 | * Returns: Zero on success; @-1@ on failure. \ |
| 259 | * \ |
| 260 | * Use: Completes an GCM encryption operation. The @aad@ \ |
| 261 | * pointer may be null if there is no additional \ |
| 262 | * authenticated data. GCM doesn't buffer ciphertext, but \ |
| 263 | * the output buffer is provided anyway for consistency \ |
| 264 | * with other AEAD schemes which don't have this property; \ |
| 265 | * the function will fail if the output buffer is broken. \ |
| 266 | */ \ |
| 267 | \ |
| 268 | extern int pre##_gcmencryptdone(pre##_gcmctx */*ctx*/, \ |
| 269 | const pre##_gcmaadctx */*aad*/, \ |
| 270 | buf */*dst*/, \ |
| 271 | void */*tag*/, size_t /*tsz*/); \ |
| 272 | \ |
| 273 | /* --- @pre_gcmdecryptdone@ --- * \ |
| 274 | * \ |
| 275 | * Arguments: @pre_gcmctx *ctx@ = pointer to an GCM context \ |
| 276 | * @const pre_gcmaadctx *aad@ = pointer to AAD context, or \ |
| 277 | * null \ |
| 278 | * @buf *dst@ = buffer for remaining plaintext \ |
| 279 | * @const void *tag@ = tag to verify \ |
| 280 | * @size_t tsz@ = length of tag \ |
| 281 | * \ |
| 282 | * Returns: @+1@ for complete success; @0@ if tag verification \ |
| 283 | * failed; @-1@ for other kinds of errors. \ |
| 284 | * \ |
| 285 | * Use: Completes an GCM decryption operation. The @aad@ \ |
| 286 | * pointer may be null if there is no additional \ |
| 287 | * authenticated data. GCM doesn't buffer plaintext, but \ |
| 288 | * the output buffer is provided anyway for consistency \ |
| 289 | * with other AEAD schemes which don't have this property; \ |
| 290 | * the function will fail if the output buffer is broken. \ |
| 291 | */ \ |
| 292 | \ |
| 293 | extern int pre##_gcmdecryptdone(pre##_gcmctx */*ctx*/, \ |
| 294 | const pre##_gcmaadctx */*aad*/, \ |
| 295 | buf */*dst*/, \ |
| 296 | const void */*tag*/, size_t /*tsz*/); \ |
| 297 | \ |
| 298 | /* --- Generic AEAD interface --- */ \ |
| 299 | \ |
| 300 | extern const gcaead pre##_gcm; |
| 301 | |
| 302 | /*----- That's all, folks -------------------------------------------------*/ |
| 303 | |
| 304 | #ifdef __cplusplus |
| 305 | } |
| 306 | #endif |
| 307 | |
| 308 | #endif |