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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Minimal library implementation of AES in CFB mode
4 *
5 * Copyright 2023 Google LLC
6 */
7
8#include <crypto/aes.h>
9#include <crypto/utils.h>
10#include <linux/export.h>
11#include <linux/module.h>
12
13/**
14 * aescfb_encrypt - Perform AES-CFB encryption on a block of data
15 *
16 * @key: The AES-CFB key schedule
17 * @dst: Pointer to the ciphertext output buffer
18 * @src: Pointer the plaintext (may equal @dst for encryption in place)
19 * @len: The size in bytes of the plaintext and ciphertext.
20 * @iv: The initialization vector (IV) to use for this block of data
21 */
22void aescfb_encrypt(const struct aes_enckey *key, u8 *dst, const u8 *src,
23 int len, const u8 iv[AES_BLOCK_SIZE])
24{
25 u8 ks[AES_BLOCK_SIZE];
26 const u8 *v = iv;
27
28 while (len > 0) {
29 aes_encrypt(key, ks, v);
30 crypto_xor_cpy(dst, src, ks, min(len, AES_BLOCK_SIZE));
31 v = dst;
32
33 dst += AES_BLOCK_SIZE;
34 src += AES_BLOCK_SIZE;
35 len -= AES_BLOCK_SIZE;
36 }
37
38 memzero_explicit(ks, sizeof(ks));
39}
40EXPORT_SYMBOL(aescfb_encrypt);
41
42/**
43 * aescfb_decrypt - Perform AES-CFB decryption on a block of data
44 *
45 * @key: The AES-CFB key schedule
46 * @dst: Pointer to the plaintext output buffer
47 * @src: Pointer the ciphertext (may equal @dst for decryption in place)
48 * @len: The size in bytes of the plaintext and ciphertext.
49 * @iv: The initialization vector (IV) to use for this block of data
50 */
51void aescfb_decrypt(const struct aes_enckey *key, u8 *dst, const u8 *src,
52 int len, const u8 iv[AES_BLOCK_SIZE])
53{
54 u8 ks[2][AES_BLOCK_SIZE];
55
56 aes_encrypt(key, ks[0], iv);
57
58 for (int i = 0; len > 0; i ^= 1) {
59 if (len > AES_BLOCK_SIZE)
60 /*
61 * Generate the keystream for the next block before
62 * performing the XOR, as that may update in place and
63 * overwrite the ciphertext.
64 */
65 aes_encrypt(key, ks[!i], src);
66
67 crypto_xor_cpy(dst, src, ks[i], min(len, AES_BLOCK_SIZE));
68
69 dst += AES_BLOCK_SIZE;
70 src += AES_BLOCK_SIZE;
71 len -= AES_BLOCK_SIZE;
72 }
73
74 memzero_explicit(ks, sizeof(ks));
75}
76EXPORT_SYMBOL(aescfb_decrypt);
77
78MODULE_DESCRIPTION("Generic AES-CFB library");
79MODULE_AUTHOR("Ard Biesheuvel <[email protected]>");
80MODULE_LICENSE("GPL");
81
82#ifdef CONFIG_CRYPTO_SELFTESTS
83
84/*
85 * Test code below. Vectors taken from crypto/testmgr.h
86 */
87
88static struct {
89 u8 ptext[64] __nonstring;
90 u8 ctext[64] __nonstring;
91
92 u8 key[AES_MAX_KEY_SIZE] __nonstring;
93 u8 iv[AES_BLOCK_SIZE] __nonstring;
94
95 int klen;
96 int len;
97} const aescfb_tv[] __initconst = {
98 { /* From NIST SP800-38A */
99 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
100 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
101 .klen = 16,
102 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
103 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
104 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96"
105 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a"
106 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c"
107 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51"
108 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11"
109 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef"
110 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17"
111 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10",
112 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20"
113 "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a"
114 "\xc8\xa6\x45\x37\xa0\xb3\xa9\x3f"
115 "\xcd\xe3\xcd\xad\x9f\x1c\xe5\x8b"
116 "\x26\x75\x1f\x67\xa3\xcb\xb1\x40"
117 "\xb1\x80\x8c\xf1\x87\xa4\xf4\xdf"
118 "\xc0\x4b\x05\x35\x7c\x5d\x1c\x0e"
119 "\xea\xc4\xc6\x6f\x9f\xf7\xf2\xe6",
120 .len = 64,
121 }, {
122 .key = "\x8e\x73\xb0\xf7\xda\x0e\x64\x52"
123 "\xc8\x10\xf3\x2b\x80\x90\x79\xe5"
124 "\x62\xf8\xea\xd2\x52\x2c\x6b\x7b",
125 .klen = 24,
126 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
127 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
128 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96"
129 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a"
130 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c"
131 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51"
132 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11"
133 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef"
134 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17"
135 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10",
136 .ctext = "\xcd\xc8\x0d\x6f\xdd\xf1\x8c\xab"
137 "\x34\xc2\x59\x09\xc9\x9a\x41\x74"
138 "\x67\xce\x7f\x7f\x81\x17\x36\x21"
139 "\x96\x1a\x2b\x70\x17\x1d\x3d\x7a"
140 "\x2e\x1e\x8a\x1d\xd5\x9b\x88\xb1"
141 "\xc8\xe6\x0f\xed\x1e\xfa\xc4\xc9"
142 "\xc0\x5f\x9f\x9c\xa9\x83\x4f\xa0"
143 "\x42\xae\x8f\xba\x58\x4b\x09\xff",
144 .len = 64,
145 }, {
146 .key = "\x60\x3d\xeb\x10\x15\xca\x71\xbe"
147 "\x2b\x73\xae\xf0\x85\x7d\x77\x81"
148 "\x1f\x35\x2c\x07\x3b\x61\x08\xd7"
149 "\x2d\x98\x10\xa3\x09\x14\xdf\xf4",
150 .klen = 32,
151 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
152 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
153 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96"
154 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a"
155 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c"
156 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51"
157 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11"
158 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef"
159 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17"
160 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10",
161 .ctext = "\xdc\x7e\x84\xbf\xda\x79\x16\x4b"
162 "\x7e\xcd\x84\x86\x98\x5d\x38\x60"
163 "\x39\xff\xed\x14\x3b\x28\xb1\xc8"
164 "\x32\x11\x3c\x63\x31\xe5\x40\x7b"
165 "\xdf\x10\x13\x24\x15\xe5\x4b\x92"
166 "\xa1\x3e\xd0\xa8\x26\x7a\xe2\xf9"
167 "\x75\xa3\x85\x74\x1a\xb9\xce\xf8"
168 "\x20\x31\x62\x3d\x55\xb1\xe4\x71",
169 .len = 64,
170 }, { /* > 16 bytes, not a multiple of 16 bytes */
171 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
172 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
173 .klen = 16,
174 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
175 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
176 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96"
177 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a"
178 "\xae",
179 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20"
180 "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a"
181 "\xc8",
182 .len = 17,
183 }, { /* < 16 bytes */
184 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6"
185 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c",
186 .klen = 16,
187 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07"
188 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
189 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f",
190 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad",
191 .len = 7,
192 },
193};
194
195static int __init libaescfb_init(void)
196{
197 for (int i = 0; i < ARRAY_SIZE(aescfb_tv); i++) {
198 struct aes_enckey key;
199 u8 buf[64];
200
201 if (aes_prepareenckey(&key, aescfb_tv[i].key, aescfb_tv[i].klen)) {
202 pr_err("aes_prepareenckey() failed on vector %d\n", i);
203 return -ENODEV;
204 }
205
206 aescfb_encrypt(&key, buf, aescfb_tv[i].ptext, aescfb_tv[i].len,
207 aescfb_tv[i].iv);
208 if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) {
209 pr_err("aescfb_encrypt() #1 failed on vector %d\n", i);
210 return -ENODEV;
211 }
212
213 /* decrypt in place */
214 aescfb_decrypt(&key, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv);
215 if (memcmp(buf, aescfb_tv[i].ptext, aescfb_tv[i].len)) {
216 pr_err("aescfb_decrypt() failed on vector %d\n", i);
217 return -ENODEV;
218 }
219
220 /* encrypt in place */
221 aescfb_encrypt(&key, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv);
222 if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) {
223 pr_err("aescfb_encrypt() #2 failed on vector %d\n", i);
224
225 return -ENODEV;
226 }
227
228 }
229 return 0;
230}
231module_init(libaescfb_init);
232
233static void __exit libaescfb_exit(void)
234{
235}
236module_exit(libaescfb_exit);
237#endif