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191 lines
5.3 KiB
191 lines
5.3 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* XCTR: XOR Counter mode - Adapted from ctr.c |
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* |
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* (C) Copyright IBM Corp. 2007 - Joy Latten <[email protected]> |
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* Copyright 2021 Google LLC |
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*/ |
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/* |
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* XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is |
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* closely related to the CTR mode of operation; the main difference is that CTR |
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* generates the keystream using E(CTR + IV) whereas XCTR generates the |
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* keystream using E(CTR ^ IV). This allows implementations to avoid dealing |
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* with multi-limb integers (as is required in CTR mode). XCTR is also specified |
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* using little-endian arithmetic which makes it slightly faster on LE machines. |
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* |
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* See the HCTR2 paper for more details: |
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* Length-preserving encryption with HCTR2 |
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* (https://eprint.iacr.org/2021/1441.pdf) |
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*/ |
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#include <crypto/algapi.h> |
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#include <crypto/internal/cipher.h> |
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#include <crypto/internal/skcipher.h> |
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#include <linux/err.h> |
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#include <linux/init.h> |
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#include <linux/kernel.h> |
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#include <linux/module.h> |
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#include <linux/slab.h> |
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/* For now this implementation is limited to 16-byte blocks for simplicity */ |
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#define XCTR_BLOCKSIZE 16 |
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static void crypto_xctr_crypt_final(struct skcipher_walk *walk, |
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struct crypto_cipher *tfm, u32 byte_ctr) |
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{ |
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u8 keystream[XCTR_BLOCKSIZE]; |
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const u8 *src = walk->src.virt.addr; |
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u8 *dst = walk->dst.virt.addr; |
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unsigned int nbytes = walk->nbytes; |
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__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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crypto_cipher_encrypt_one(tfm, keystream, walk->iv); |
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crypto_xor_cpy(dst, keystream, src, nbytes); |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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} |
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static int crypto_xctr_crypt_segment(struct skcipher_walk *walk, |
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struct crypto_cipher *tfm, u32 byte_ctr) |
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{ |
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void (*fn)(struct crypto_tfm *, u8 *, const u8 *) = |
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crypto_cipher_alg(tfm)->cia_encrypt; |
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const u8 *src = walk->src.virt.addr; |
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u8 *dst = walk->dst.virt.addr; |
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unsigned int nbytes = walk->nbytes; |
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__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); |
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do { |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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fn(crypto_cipher_tfm(tfm), dst, walk->iv); |
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crypto_xor(dst, src, XCTR_BLOCKSIZE); |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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le32_add_cpu(&ctr32, 1); |
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src += XCTR_BLOCKSIZE; |
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dst += XCTR_BLOCKSIZE; |
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} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE); |
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return nbytes; |
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} |
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static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk, |
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struct crypto_cipher *tfm, u32 byte_ctr) |
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{ |
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void (*fn)(struct crypto_tfm *, u8 *, const u8 *) = |
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crypto_cipher_alg(tfm)->cia_encrypt; |
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unsigned long alignmask = crypto_cipher_alignmask(tfm); |
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unsigned int nbytes = walk->nbytes; |
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u8 *data = walk->src.virt.addr; |
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u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK]; |
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u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); |
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__le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); |
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do { |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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fn(crypto_cipher_tfm(tfm), keystream, walk->iv); |
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crypto_xor(data, keystream, XCTR_BLOCKSIZE); |
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crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); |
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le32_add_cpu(&ctr32, 1); |
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data += XCTR_BLOCKSIZE; |
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} while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE); |
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return nbytes; |
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} |
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static int crypto_xctr_crypt(struct skcipher_request *req) |
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{ |
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); |
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struct crypto_cipher *cipher = skcipher_cipher_simple(tfm); |
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struct skcipher_walk walk; |
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unsigned int nbytes; |
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int err; |
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u32 byte_ctr = 0; |
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err = skcipher_walk_virt(&walk, req, false); |
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while (walk.nbytes >= XCTR_BLOCKSIZE) { |
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if (walk.src.virt.addr == walk.dst.virt.addr) |
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nbytes = crypto_xctr_crypt_inplace(&walk, cipher, |
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byte_ctr); |
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else |
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nbytes = crypto_xctr_crypt_segment(&walk, cipher, |
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byte_ctr); |
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byte_ctr += walk.nbytes - nbytes; |
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err = skcipher_walk_done(&walk, nbytes); |
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} |
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if (walk.nbytes) { |
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crypto_xctr_crypt_final(&walk, cipher, byte_ctr); |
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err = skcipher_walk_done(&walk, 0); |
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} |
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return err; |
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} |
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static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb) |
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{ |
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struct skcipher_instance *inst; |
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struct crypto_alg *alg; |
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int err; |
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inst = skcipher_alloc_instance_simple(tmpl, tb); |
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if (IS_ERR(inst)) |
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return PTR_ERR(inst); |
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alg = skcipher_ialg_simple(inst); |
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/* Block size must be 16 bytes. */ |
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err = -EINVAL; |
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if (alg->cra_blocksize != XCTR_BLOCKSIZE) |
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goto out_free_inst; |
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/* XCTR mode is a stream cipher. */ |
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inst->alg.base.cra_blocksize = 1; |
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/* |
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* To simplify the implementation, configure the skcipher walk to only |
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* give a partial block at the very end, never earlier. |
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*/ |
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inst->alg.chunksize = alg->cra_blocksize; |
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inst->alg.encrypt = crypto_xctr_crypt; |
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inst->alg.decrypt = crypto_xctr_crypt; |
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err = skcipher_register_instance(tmpl, inst); |
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if (err) { |
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out_free_inst: |
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inst->free(inst); |
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} |
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return err; |
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} |
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static struct crypto_template crypto_xctr_tmpl = { |
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.name = "xctr", |
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.create = crypto_xctr_create, |
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.module = THIS_MODULE, |
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}; |
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static int __init crypto_xctr_module_init(void) |
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{ |
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return crypto_register_template(&crypto_xctr_tmpl); |
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} |
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static void __exit crypto_xctr_module_exit(void) |
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{ |
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crypto_unregister_template(&crypto_xctr_tmpl); |
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} |
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subsys_initcall(crypto_xctr_module_init); |
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module_exit(crypto_xctr_module_exit); |
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MODULE_LICENSE("GPL"); |
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MODULE_DESCRIPTION("XCTR block cipher mode of operation"); |
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MODULE_ALIAS_CRYPTO("xctr"); |
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MODULE_IMPORT_NS(CRYPTO_INTERNAL);
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