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 <linux/module.h> 9 10 #include <crypto/algapi.h> 11 #include <crypto/aes.h> 12 13 #include <asm/irqflags.h> 14 15 static void aescfb_encrypt_block(const struct crypto_aes_ctx *ctx, void *dst, 16 const void *src) 17 { 18 unsigned long flags; 19 20 /* 21 * In AES-CFB, the AES encryption operates on known 'plaintext' (the IV 22 * and ciphertext), making it susceptible to timing attacks on the 23 * encryption key. The AES library already mitigates this risk to some 24 * extent by pulling the entire S-box into the caches before doing any 25 * substitutions, but this strategy is more effective when running with 26 * interrupts disabled. 27 */ 28 local_irq_save(flags); 29 aes_encrypt(ctx, dst, src); 30 local_irq_restore(flags); 31 } 32 33 /** 34 * aescfb_encrypt - Perform AES-CFB encryption on a block of data 35 * 36 * @ctx: The AES-CFB key schedule 37 * @dst: Pointer to the ciphertext output buffer 38 * @src: Pointer the plaintext (may equal @dst for encryption in place) 39 * @len: The size in bytes of the plaintext and ciphertext. 40 * @iv: The initialization vector (IV) to use for this block of data 41 */ 42 void aescfb_encrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, 43 int len, const u8 iv[AES_BLOCK_SIZE]) 44 { 45 u8 ks[AES_BLOCK_SIZE]; 46 const u8 *v = iv; 47 48 while (len > 0) { 49 aescfb_encrypt_block(ctx, ks, v); 50 crypto_xor_cpy(dst, src, ks, min(len, AES_BLOCK_SIZE)); 51 v = dst; 52 53 dst += AES_BLOCK_SIZE; 54 src += AES_BLOCK_SIZE; 55 len -= AES_BLOCK_SIZE; 56 } 57 58 memzero_explicit(ks, sizeof(ks)); 59 } 60 EXPORT_SYMBOL(aescfb_encrypt); 61 62 /** 63 * aescfb_decrypt - Perform AES-CFB decryption on a block of data 64 * 65 * @ctx: The AES-CFB key schedule 66 * @dst: Pointer to the plaintext output buffer 67 * @src: Pointer the ciphertext (may equal @dst for decryption in place) 68 * @len: The size in bytes of the plaintext and ciphertext. 69 * @iv: The initialization vector (IV) to use for this block of data 70 */ 71 void aescfb_decrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, 72 int len, const u8 iv[AES_BLOCK_SIZE]) 73 { 74 u8 ks[2][AES_BLOCK_SIZE]; 75 76 aescfb_encrypt_block(ctx, ks[0], iv); 77 78 for (int i = 0; len > 0; i ^= 1) { 79 if (len > AES_BLOCK_SIZE) 80 /* 81 * Generate the keystream for the next block before 82 * performing the XOR, as that may update in place and 83 * overwrite the ciphertext. 84 */ 85 aescfb_encrypt_block(ctx, ks[!i], src); 86 87 crypto_xor_cpy(dst, src, ks[i], min(len, AES_BLOCK_SIZE)); 88 89 dst += AES_BLOCK_SIZE; 90 src += AES_BLOCK_SIZE; 91 len -= AES_BLOCK_SIZE; 92 } 93 94 memzero_explicit(ks, sizeof(ks)); 95 } 96 EXPORT_SYMBOL(aescfb_decrypt); 97 98 MODULE_DESCRIPTION("Generic AES-CFB library"); 99 MODULE_AUTHOR("Ard Biesheuvel <ardb@kernel.org>"); 100 MODULE_LICENSE("GPL"); 101 102 #ifndef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS 103 104 /* 105 * Test code below. Vectors taken from crypto/testmgr.h 106 */ 107 108 static struct { 109 u8 ptext[64]; 110 u8 ctext[64]; 111 112 u8 key[AES_MAX_KEY_SIZE]; 113 u8 iv[AES_BLOCK_SIZE]; 114 115 int klen; 116 int len; 117 } const aescfb_tv[] __initconst = { 118 { /* From NIST SP800-38A */ 119 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" 120 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", 121 .klen = 16, 122 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" 123 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", 124 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" 125 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" 126 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" 127 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" 128 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" 129 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" 130 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" 131 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", 132 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" 133 "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" 134 "\xc8\xa6\x45\x37\xa0\xb3\xa9\x3f" 135 "\xcd\xe3\xcd\xad\x9f\x1c\xe5\x8b" 136 "\x26\x75\x1f\x67\xa3\xcb\xb1\x40" 137 "\xb1\x80\x8c\xf1\x87\xa4\xf4\xdf" 138 "\xc0\x4b\x05\x35\x7c\x5d\x1c\x0e" 139 "\xea\xc4\xc6\x6f\x9f\xf7\xf2\xe6", 140 .len = 64, 141 }, { 142 .key = "\x8e\x73\xb0\xf7\xda\x0e\x64\x52" 143 "\xc8\x10\xf3\x2b\x80\x90\x79\xe5" 144 "\x62\xf8\xea\xd2\x52\x2c\x6b\x7b", 145 .klen = 24, 146 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" 147 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", 148 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" 149 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" 150 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" 151 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" 152 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" 153 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" 154 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" 155 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", 156 .ctext = "\xcd\xc8\x0d\x6f\xdd\xf1\x8c\xab" 157 "\x34\xc2\x59\x09\xc9\x9a\x41\x74" 158 "\x67\xce\x7f\x7f\x81\x17\x36\x21" 159 "\x96\x1a\x2b\x70\x17\x1d\x3d\x7a" 160 "\x2e\x1e\x8a\x1d\xd5\x9b\x88\xb1" 161 "\xc8\xe6\x0f\xed\x1e\xfa\xc4\xc9" 162 "\xc0\x5f\x9f\x9c\xa9\x83\x4f\xa0" 163 "\x42\xae\x8f\xba\x58\x4b\x09\xff", 164 .len = 64, 165 }, { 166 .key = "\x60\x3d\xeb\x10\x15\xca\x71\xbe" 167 "\x2b\x73\xae\xf0\x85\x7d\x77\x81" 168 "\x1f\x35\x2c\x07\x3b\x61\x08\xd7" 169 "\x2d\x98\x10\xa3\x09\x14\xdf\xf4", 170 .klen = 32, 171 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" 172 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", 173 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" 174 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" 175 "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" 176 "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" 177 "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" 178 "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" 179 "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" 180 "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", 181 .ctext = "\xdc\x7e\x84\xbf\xda\x79\x16\x4b" 182 "\x7e\xcd\x84\x86\x98\x5d\x38\x60" 183 "\x39\xff\xed\x14\x3b\x28\xb1\xc8" 184 "\x32\x11\x3c\x63\x31\xe5\x40\x7b" 185 "\xdf\x10\x13\x24\x15\xe5\x4b\x92" 186 "\xa1\x3e\xd0\xa8\x26\x7a\xe2\xf9" 187 "\x75\xa3\x85\x74\x1a\xb9\xce\xf8" 188 "\x20\x31\x62\x3d\x55\xb1\xe4\x71", 189 .len = 64, 190 }, { /* > 16 bytes, not a multiple of 16 bytes */ 191 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" 192 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", 193 .klen = 16, 194 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" 195 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", 196 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" 197 "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" 198 "\xae", 199 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" 200 "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" 201 "\xc8", 202 .len = 17, 203 }, { /* < 16 bytes */ 204 .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" 205 "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", 206 .klen = 16, 207 .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" 208 "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", 209 .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f", 210 .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad", 211 .len = 7, 212 }, 213 }; 214 215 static int __init libaescfb_init(void) 216 { 217 for (int i = 0; i < ARRAY_SIZE(aescfb_tv); i++) { 218 struct crypto_aes_ctx ctx; 219 u8 buf[64]; 220 221 if (aes_expandkey(&ctx, aescfb_tv[i].key, aescfb_tv[i].klen)) { 222 pr_err("aes_expandkey() failed on vector %d\n", i); 223 return -ENODEV; 224 } 225 226 aescfb_encrypt(&ctx, buf, aescfb_tv[i].ptext, aescfb_tv[i].len, 227 aescfb_tv[i].iv); 228 if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { 229 pr_err("aescfb_encrypt() #1 failed on vector %d\n", i); 230 return -ENODEV; 231 } 232 233 /* decrypt in place */ 234 aescfb_decrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); 235 if (memcmp(buf, aescfb_tv[i].ptext, aescfb_tv[i].len)) { 236 pr_err("aescfb_decrypt() failed on vector %d\n", i); 237 return -ENODEV; 238 } 239 240 /* encrypt in place */ 241 aescfb_encrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); 242 if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { 243 pr_err("aescfb_encrypt() #2 failed on vector %d\n", i); 244 245 return -ENODEV; 246 } 247 248 } 249 return 0; 250 } 251 module_init(libaescfb_init); 252 253 static void __exit libaescfb_exit(void) 254 { 255 } 256 module_exit(libaescfb_exit); 257 #endif 258