// SPDX-License-Identifier: GPL-2.0 /* * Minimal library implementation of AES in CFB mode * * Copyright 2023 Google LLC */ #include #include #include #include static void aescfb_encrypt_block(const struct crypto_aes_ctx *ctx, void *dst, const void *src) { unsigned long flags; /* * In AES-CFB, the AES encryption operates on known 'plaintext' (the IV * and ciphertext), making it susceptible to timing attacks on the * encryption key. The AES library already mitigates this risk to some * extent by pulling the entire S-box into the caches before doing any * substitutions, but this strategy is more effective when running with * interrupts disabled. */ local_irq_save(flags); aes_encrypt(ctx, dst, src); local_irq_restore(flags); } /** * aescfb_encrypt - Perform AES-CFB encryption on a block of data * * @ctx: The AES-CFB key schedule * @dst: Pointer to the ciphertext output buffer * @src: Pointer the plaintext (may equal @dst for encryption in place) * @len: The size in bytes of the plaintext and ciphertext. * @iv: The initialization vector (IV) to use for this block of data */ void aescfb_encrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, int len, const u8 iv[AES_BLOCK_SIZE]) { u8 ks[AES_BLOCK_SIZE]; const u8 *v = iv; while (len > 0) { aescfb_encrypt_block(ctx, ks, v); crypto_xor_cpy(dst, src, ks, min(len, AES_BLOCK_SIZE)); v = dst; dst += AES_BLOCK_SIZE; src += AES_BLOCK_SIZE; len -= AES_BLOCK_SIZE; } memzero_explicit(ks, sizeof(ks)); } EXPORT_SYMBOL(aescfb_encrypt); /** * aescfb_decrypt - Perform AES-CFB decryption on a block of data * * @ctx: The AES-CFB key schedule * @dst: Pointer to the plaintext output buffer * @src: Pointer the ciphertext (may equal @dst for decryption in place) * @len: The size in bytes of the plaintext and ciphertext. * @iv: The initialization vector (IV) to use for this block of data */ void aescfb_decrypt(const struct crypto_aes_ctx *ctx, u8 *dst, const u8 *src, int len, const u8 iv[AES_BLOCK_SIZE]) { u8 ks[2][AES_BLOCK_SIZE]; aescfb_encrypt_block(ctx, ks[0], iv); for (int i = 0; len > 0; i ^= 1) { if (len > AES_BLOCK_SIZE) /* * Generate the keystream for the next block before * performing the XOR, as that may update in place and * overwrite the ciphertext. */ aescfb_encrypt_block(ctx, ks[!i], src); crypto_xor_cpy(dst, src, ks[i], min(len, AES_BLOCK_SIZE)); dst += AES_BLOCK_SIZE; src += AES_BLOCK_SIZE; len -= AES_BLOCK_SIZE; } memzero_explicit(ks, sizeof(ks)); } EXPORT_SYMBOL(aescfb_decrypt); MODULE_DESCRIPTION("Generic AES-CFB library"); MODULE_AUTHOR("Ard Biesheuvel "); MODULE_LICENSE("GPL"); #ifndef CONFIG_CRYPTO_MANAGER_DISABLE_TESTS /* * Test code below. Vectors taken from crypto/testmgr.h */ static struct { u8 ptext[64]; u8 ctext[64]; u8 key[AES_MAX_KEY_SIZE]; u8 iv[AES_BLOCK_SIZE]; int klen; int len; } const aescfb_tv[] __initconst = { { /* From NIST SP800-38A */ .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", .klen = 16, .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" "\xc8\xa6\x45\x37\xa0\xb3\xa9\x3f" "\xcd\xe3\xcd\xad\x9f\x1c\xe5\x8b" "\x26\x75\x1f\x67\xa3\xcb\xb1\x40" "\xb1\x80\x8c\xf1\x87\xa4\xf4\xdf" "\xc0\x4b\x05\x35\x7c\x5d\x1c\x0e" "\xea\xc4\xc6\x6f\x9f\xf7\xf2\xe6", .len = 64, }, { .key = "\x8e\x73\xb0\xf7\xda\x0e\x64\x52" "\xc8\x10\xf3\x2b\x80\x90\x79\xe5" "\x62\xf8\xea\xd2\x52\x2c\x6b\x7b", .klen = 24, .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", .ctext = "\xcd\xc8\x0d\x6f\xdd\xf1\x8c\xab" "\x34\xc2\x59\x09\xc9\x9a\x41\x74" "\x67\xce\x7f\x7f\x81\x17\x36\x21" "\x96\x1a\x2b\x70\x17\x1d\x3d\x7a" "\x2e\x1e\x8a\x1d\xd5\x9b\x88\xb1" "\xc8\xe6\x0f\xed\x1e\xfa\xc4\xc9" "\xc0\x5f\x9f\x9c\xa9\x83\x4f\xa0" "\x42\xae\x8f\xba\x58\x4b\x09\xff", .len = 64, }, { .key = "\x60\x3d\xeb\x10\x15\xca\x71\xbe" "\x2b\x73\xae\xf0\x85\x7d\x77\x81" "\x1f\x35\x2c\x07\x3b\x61\x08\xd7" "\x2d\x98\x10\xa3\x09\x14\xdf\xf4", .klen = 32, .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" "\xae\x2d\x8a\x57\x1e\x03\xac\x9c" "\x9e\xb7\x6f\xac\x45\xaf\x8e\x51" "\x30\xc8\x1c\x46\xa3\x5c\xe4\x11" "\xe5\xfb\xc1\x19\x1a\x0a\x52\xef" "\xf6\x9f\x24\x45\xdf\x4f\x9b\x17" "\xad\x2b\x41\x7b\xe6\x6c\x37\x10", .ctext = "\xdc\x7e\x84\xbf\xda\x79\x16\x4b" "\x7e\xcd\x84\x86\x98\x5d\x38\x60" "\x39\xff\xed\x14\x3b\x28\xb1\xc8" "\x32\x11\x3c\x63\x31\xe5\x40\x7b" "\xdf\x10\x13\x24\x15\xe5\x4b\x92" "\xa1\x3e\xd0\xa8\x26\x7a\xe2\xf9" "\x75\xa3\x85\x74\x1a\xb9\xce\xf8" "\x20\x31\x62\x3d\x55\xb1\xe4\x71", .len = 64, }, { /* > 16 bytes, not a multiple of 16 bytes */ .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", .klen = 16, .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f\x96" "\xe9\x3d\x7e\x11\x73\x93\x17\x2a" "\xae", .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad\x20" "\x33\x34\x49\xf8\xe8\x3c\xfb\x4a" "\xc8", .len = 17, }, { /* < 16 bytes */ .key = "\x2b\x7e\x15\x16\x28\xae\xd2\xa6" "\xab\xf7\x15\x88\x09\xcf\x4f\x3c", .klen = 16, .iv = "\x00\x01\x02\x03\x04\x05\x06\x07" "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f", .ptext = "\x6b\xc1\xbe\xe2\x2e\x40\x9f", .ctext = "\x3b\x3f\xd9\x2e\xb7\x2d\xad", .len = 7, }, }; static int __init libaescfb_init(void) { for (int i = 0; i < ARRAY_SIZE(aescfb_tv); i++) { struct crypto_aes_ctx ctx; u8 buf[64]; if (aes_expandkey(&ctx, aescfb_tv[i].key, aescfb_tv[i].klen)) { pr_err("aes_expandkey() failed on vector %d\n", i); return -ENODEV; } aescfb_encrypt(&ctx, buf, aescfb_tv[i].ptext, aescfb_tv[i].len, aescfb_tv[i].iv); if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { pr_err("aescfb_encrypt() #1 failed on vector %d\n", i); return -ENODEV; } /* decrypt in place */ aescfb_decrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); if (memcmp(buf, aescfb_tv[i].ptext, aescfb_tv[i].len)) { pr_err("aescfb_decrypt() failed on vector %d\n", i); return -ENODEV; } /* encrypt in place */ aescfb_encrypt(&ctx, buf, buf, aescfb_tv[i].len, aescfb_tv[i].iv); if (memcmp(buf, aescfb_tv[i].ctext, aescfb_tv[i].len)) { pr_err("aescfb_encrypt() #2 failed on vector %d\n", i); return -ENODEV; } } return 0; } module_init(libaescfb_init); static void __exit libaescfb_exit(void) { } module_exit(libaescfb_exit); #endif