xref: /freebsd/contrib/wpa/src/crypto/aes-gcm.c (revision cc16dea626cf2fc80cde667ac4798065108e596c) 
1 /*
2  * Galois/Counter Mode (GCM) and GMAC with AES
3  *
4  * Copyright (c) 2012, Jouni Malinen <j@w1.fi>
5  *
6  * This software may be distributed under the terms of the BSD license.
7  * See README for more details.
8  */
9 
10 #include "includes.h"
11 
12 #include "common.h"
13 #include "aes.h"
14 #include "aes_wrap.h"
15 
16 static void inc32(u8 *block)
17 {
18 	u32 val;
19 	val = WPA_GET_BE32(block + AES_BLOCK_SIZE - 4);
20 	val++;
21 	WPA_PUT_BE32(block + AES_BLOCK_SIZE - 4, val);
22 }
23 
24 
25 static void xor_block(u8 *dst, const u8 *src)
26 {
27 	u32 *d = (u32 *) dst;
28 	u32 *s = (u32 *) src;
29 	*d++ ^= *s++;
30 	*d++ ^= *s++;
31 	*d++ ^= *s++;
32 	*d++ ^= *s++;
33 }
34 
35 
36 static void shift_right_block(u8 *v)
37 {
38 	u32 val;
39 
40 	val = WPA_GET_BE32(v + 12);
41 	val >>= 1;
42 	if (v[11] & 0x01)
43 		val |= 0x80000000;
44 	WPA_PUT_BE32(v + 12, val);
45 
46 	val = WPA_GET_BE32(v + 8);
47 	val >>= 1;
48 	if (v[7] & 0x01)
49 		val |= 0x80000000;
50 	WPA_PUT_BE32(v + 8, val);
51 
52 	val = WPA_GET_BE32(v + 4);
53 	val >>= 1;
54 	if (v[3] & 0x01)
55 		val |= 0x80000000;
56 	WPA_PUT_BE32(v + 4, val);
57 
58 	val = WPA_GET_BE32(v);
59 	val >>= 1;
60 	WPA_PUT_BE32(v, val);
61 }
62 
63 
64 /* Multiplication in GF(2^128) */
65 static void gf_mult(const u8 *x, const u8 *y, u8 *z)
66 {
67 	u8 v[16];
68 	int i, j;
69 
70 	os_memset(z, 0, 16); /* Z_0 = 0^128 */
71 	os_memcpy(v, y, 16); /* V_0 = Y */
72 
73 	for (i = 0; i < 16; i++) {
74 		for (j = 0; j < 8; j++) {
75 			if (x[i] & BIT(7 - j)) {
76 				/* Z_(i + 1) = Z_i XOR V_i */
77 				xor_block(z, v);
78 			} else {
79 				/* Z_(i + 1) = Z_i */
80 			}
81 
82 			if (v[15] & 0x01) {
83 				/* V_(i + 1) = (V_i >> 1) XOR R */
84 				shift_right_block(v);
85 				/* R = 11100001 || 0^120 */
86 				v[0] ^= 0xe1;
87 			} else {
88 				/* V_(i + 1) = V_i >> 1 */
89 				shift_right_block(v);
90 			}
91 		}
92 	}
93 }
94 
95 
96 static void ghash_start(u8 *y)
97 {
98 	/* Y_0 = 0^128 */
99 	os_memset(y, 0, 16);
100 }
101 
102 
103 static void ghash(const u8 *h, const u8 *x, size_t xlen, u8 *y)
104 {
105 	size_t m, i;
106 	const u8 *xpos = x;
107 	u8 tmp[16];
108 
109 	m = xlen / 16;
110 
111 	for (i = 0; i < m; i++) {
112 		/* Y_i = (Y^(i-1) XOR X_i) dot H */
113 		xor_block(y, xpos);
114 		xpos += 16;
115 
116 		/* dot operation:
117 		 * multiplication operation for binary Galois (finite) field of
118 		 * 2^128 elements */
119 		gf_mult(y, h, tmp);
120 		os_memcpy(y, tmp, 16);
121 	}
122 
123 	if (x + xlen > xpos) {
124 		/* Add zero padded last block */
125 		size_t last = x + xlen - xpos;
126 		os_memcpy(tmp, xpos, last);
127 		os_memset(tmp + last, 0, sizeof(tmp) - last);
128 
129 		/* Y_i = (Y^(i-1) XOR X_i) dot H */
130 		xor_block(y, tmp);
131 
132 		/* dot operation:
133 		 * multiplication operation for binary Galois (finite) field of
134 		 * 2^128 elements */
135 		gf_mult(y, h, tmp);
136 		os_memcpy(y, tmp, 16);
137 	}
138 
139 	/* Return Y_m */
140 }
141 
142 
143 static void aes_gctr(void *aes, const u8 *icb, const u8 *x, size_t xlen, u8 *y)
144 {
145 	size_t i, n, last;
146 	u8 cb[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE];
147 	const u8 *xpos = x;
148 	u8 *ypos = y;
149 
150 	if (xlen == 0)
151 		return;
152 
153 	n = xlen / 16;
154 
155 	os_memcpy(cb, icb, AES_BLOCK_SIZE);
156 	/* Full blocks */
157 	for (i = 0; i < n; i++) {
158 		aes_encrypt(aes, cb, ypos);
159 		xor_block(ypos, xpos);
160 		xpos += AES_BLOCK_SIZE;
161 		ypos += AES_BLOCK_SIZE;
162 		inc32(cb);
163 	}
164 
165 	last = x + xlen - xpos;
166 	if (last) {
167 		/* Last, partial block */
168 		aes_encrypt(aes, cb, tmp);
169 		for (i = 0; i < last; i++)
170 			*ypos++ = *xpos++ ^ tmp[i];
171 	}
172 }
173 
174 
175 static void * aes_gcm_init_hash_subkey(const u8 *key, size_t key_len, u8 *H)
176 {
177 	void *aes;
178 
179 	aes = aes_encrypt_init(key, key_len);
180 	if (aes == NULL)
181 		return NULL;
182 
183 	/* Generate hash subkey H = AES_K(0^128) */
184 	os_memset(H, 0, AES_BLOCK_SIZE);
185 	aes_encrypt(aes, H, H);
186 	wpa_hexdump_key(MSG_EXCESSIVE, "Hash subkey H for GHASH",
187 			H, AES_BLOCK_SIZE);
188 	return aes;
189 }
190 
191 
192 static void aes_gcm_prepare_j0(const u8 *iv, size_t iv_len, const u8 *H, u8 *J0)
193 {
194 	u8 len_buf[16];
195 
196 	if (iv_len == 12) {
197 		/* Prepare block J_0 = IV || 0^31 || 1 [len(IV) = 96] */
198 		os_memcpy(J0, iv, iv_len);
199 		os_memset(J0 + iv_len, 0, AES_BLOCK_SIZE - iv_len);
200 		J0[AES_BLOCK_SIZE - 1] = 0x01;
201 	} else {
202 		/*
203 		 * s = 128 * ceil(len(IV)/128) - len(IV)
204 		 * J_0 = GHASH_H(IV || 0^(s+64) || [len(IV)]_64)
205 		 */
206 		ghash_start(J0);
207 		ghash(H, iv, iv_len, J0);
208 		WPA_PUT_BE64(len_buf, 0);
209 		WPA_PUT_BE64(len_buf + 8, iv_len * 8);
210 		ghash(H, len_buf, sizeof(len_buf), J0);
211 	}
212 }
213 
214 
215 static void aes_gcm_gctr(void *aes, const u8 *J0, const u8 *in, size_t len,
216 			 u8 *out)
217 {
218 	u8 J0inc[AES_BLOCK_SIZE];
219 
220 	if (len == 0)
221 		return;
222 
223 	os_memcpy(J0inc, J0, AES_BLOCK_SIZE);
224 	inc32(J0inc);
225 	aes_gctr(aes, J0inc, in, len, out);
226 }
227 
228 
229 static void aes_gcm_ghash(const u8 *H, const u8 *aad, size_t aad_len,
230 			  const u8 *crypt, size_t crypt_len, u8 *S)
231 {
232 	u8 len_buf[16];
233 
234 	/*
235 	 * u = 128 * ceil[len(C)/128] - len(C)
236 	 * v = 128 * ceil[len(A)/128] - len(A)
237 	 * S = GHASH_H(A || 0^v || C || 0^u || [len(A)]64 || [len(C)]64)
238 	 * (i.e., zero padded to block size A || C and lengths of each in bits)
239 	 */
240 	ghash_start(S);
241 	ghash(H, aad, aad_len, S);
242 	ghash(H, crypt, crypt_len, S);
243 	WPA_PUT_BE64(len_buf, aad_len * 8);
244 	WPA_PUT_BE64(len_buf + 8, crypt_len * 8);
245 	ghash(H, len_buf, sizeof(len_buf), S);
246 
247 	wpa_hexdump_key(MSG_EXCESSIVE, "S = GHASH_H(...)", S, 16);
248 }
249 
250 
251 /**
252  * aes_gcm_ae - GCM-AE_K(IV, P, A)
253  */
254 int aes_gcm_ae(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
255 	       const u8 *plain, size_t plain_len,
256 	       const u8 *aad, size_t aad_len, u8 *crypt, u8 *tag)
257 {
258 	u8 H[AES_BLOCK_SIZE];
259 	u8 J0[AES_BLOCK_SIZE];
260 	u8 S[16];
261 	void *aes;
262 
263 	aes = aes_gcm_init_hash_subkey(key, key_len, H);
264 	if (aes == NULL)
265 		return -1;
266 
267 	aes_gcm_prepare_j0(iv, iv_len, H, J0);
268 
269 	/* C = GCTR_K(inc_32(J_0), P) */
270 	aes_gcm_gctr(aes, J0, plain, plain_len, crypt);
271 
272 	aes_gcm_ghash(H, aad, aad_len, crypt, plain_len, S);
273 
274 	/* T = MSB_t(GCTR_K(J_0, S)) */
275 	aes_gctr(aes, J0, S, sizeof(S), tag);
276 
277 	/* Return (C, T) */
278 
279 	aes_encrypt_deinit(aes);
280 
281 	return 0;
282 }
283 
284 
285 /**
286  * aes_gcm_ad - GCM-AD_K(IV, C, A, T)
287  */
288 int aes_gcm_ad(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
289 	       const u8 *crypt, size_t crypt_len,
290 	       const u8 *aad, size_t aad_len, const u8 *tag, u8 *plain)
291 {
292 	u8 H[AES_BLOCK_SIZE];
293 	u8 J0[AES_BLOCK_SIZE];
294 	u8 S[16], T[16];
295 	void *aes;
296 
297 	aes = aes_gcm_init_hash_subkey(key, key_len, H);
298 	if (aes == NULL)
299 		return -1;
300 
301 	aes_gcm_prepare_j0(iv, iv_len, H, J0);
302 
303 	/* P = GCTR_K(inc_32(J_0), C) */
304 	aes_gcm_gctr(aes, J0, crypt, crypt_len, plain);
305 
306 	aes_gcm_ghash(H, aad, aad_len, crypt, crypt_len, S);
307 
308 	/* T' = MSB_t(GCTR_K(J_0, S)) */
309 	aes_gctr(aes, J0, S, sizeof(S), T);
310 
311 	aes_encrypt_deinit(aes);
312 
313 	if (os_memcmp(tag, T, 16) != 0) {
314 		wpa_printf(MSG_EXCESSIVE, "GCM: Tag mismatch");
315 		return -1;
316 	}
317 
318 	return 0;
319 }
320 
321 
322 int aes_gmac(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
323 	     const u8 *aad, size_t aad_len, u8 *tag)
324 {
325 	return aes_gcm_ae(key, key_len, iv, iv_len, NULL, 0, aad, aad_len, NULL,
326 			  tag);
327 }
328