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Diffstat (limited to 'crypto/xctr.c')
| -rw-r--r-- | crypto/xctr.c | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/crypto/xctr.c b/crypto/xctr.c new file mode 100644 index 000000000..5c00147e8 --- /dev/null +++ b/crypto/xctr.c @@ -0,0 +1,191 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * XCTR: XOR Counter mode - Adapted from ctr.c + * + * (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com> + * Copyright 2021 Google LLC + */ + +/* + * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is + * closely related to the CTR mode of operation; the main difference is that CTR + * generates the keystream using E(CTR + IV) whereas XCTR generates the + * keystream using E(CTR ^ IV). This allows implementations to avoid dealing + * with multi-limb integers (as is required in CTR mode). XCTR is also specified + * using little-endian arithmetic which makes it slightly faster on LE machines. + * + * See the HCTR2 paper for more details: + * Length-preserving encryption with HCTR2 + * (https://eprint.iacr.org/2021/1441.pdf) + */ + +#include <crypto/algapi.h> +#include <crypto/internal/cipher.h> +#include <crypto/internal/skcipher.h> +#include <linux/err.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/slab.h> + +/* For now this implementation is limited to 16-byte blocks for simplicity */ +#define XCTR_BLOCKSIZE 16 + +static void crypto_xctr_crypt_final(struct skcipher_walk *walk, + struct crypto_cipher *tfm, u32 byte_ctr) +{ + u8 keystream[XCTR_BLOCKSIZE]; + const u8 *src = walk->src.virt.addr; + u8 *dst = walk->dst.virt.addr; + unsigned int nbytes = walk->nbytes; + __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); + + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); + crypto_cipher_encrypt_one(tfm, keystream, walk->iv); + crypto_xor_cpy(dst, keystream, src, nbytes); + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); +} + +static int crypto_xctr_crypt_segment(struct skcipher_walk *walk, + struct crypto_cipher *tfm, u32 byte_ctr) +{ + void (*fn)(struct crypto_tfm *, u8 *, const u8 *) = + crypto_cipher_alg(tfm)->cia_encrypt; + const u8 *src = walk->src.virt.addr; + u8 *dst = walk->dst.virt.addr; + unsigned int nbytes = walk->nbytes; + __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); + + do { + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); + fn(crypto_cipher_tfm(tfm), dst, walk->iv); + crypto_xor(dst, src, XCTR_BLOCKSIZE); + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); + + le32_add_cpu(&ctr32, 1); + + src += XCTR_BLOCKSIZE; + dst += XCTR_BLOCKSIZE; + } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE); + + return nbytes; +} + +static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk, + struct crypto_cipher *tfm, u32 byte_ctr) +{ + void (*fn)(struct crypto_tfm *, u8 *, const u8 *) = + crypto_cipher_alg(tfm)->cia_encrypt; + unsigned long alignmask = crypto_cipher_alignmask(tfm); + unsigned int nbytes = walk->nbytes; + u8 *data = walk->src.virt.addr; + u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK]; + u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); + __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1); + + do { + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); + fn(crypto_cipher_tfm(tfm), keystream, walk->iv); + crypto_xor(data, keystream, XCTR_BLOCKSIZE); + crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32)); + + le32_add_cpu(&ctr32, 1); + + data += XCTR_BLOCKSIZE; + } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE); + + return nbytes; +} + +static int crypto_xctr_crypt(struct skcipher_request *req) +{ + struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); + struct crypto_cipher *cipher = skcipher_cipher_simple(tfm); + struct skcipher_walk walk; + unsigned int nbytes; + int err; + u32 byte_ctr = 0; + + err = skcipher_walk_virt(&walk, req, false); + + while (walk.nbytes >= XCTR_BLOCKSIZE) { + if (walk.src.virt.addr == walk.dst.virt.addr) + nbytes = crypto_xctr_crypt_inplace(&walk, cipher, + byte_ctr); + else + nbytes = crypto_xctr_crypt_segment(&walk, cipher, + byte_ctr); + + byte_ctr += walk.nbytes - nbytes; + err = skcipher_walk_done(&walk, nbytes); + } + + if (walk.nbytes) { + crypto_xctr_crypt_final(&walk, cipher, byte_ctr); + err = skcipher_walk_done(&walk, 0); + } + + return err; +} + +static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb) +{ + struct skcipher_instance *inst; + struct crypto_alg *alg; + int err; + + inst = skcipher_alloc_instance_simple(tmpl, tb); + if (IS_ERR(inst)) + return PTR_ERR(inst); + + alg = skcipher_ialg_simple(inst); + + /* Block size must be 16 bytes. */ + err = -EINVAL; + if (alg->cra_blocksize != XCTR_BLOCKSIZE) + goto out_free_inst; + + /* XCTR mode is a stream cipher. */ + inst->alg.base.cra_blocksize = 1; + + /* + * To simplify the implementation, configure the skcipher walk to only + * give a partial block at the very end, never earlier. + */ + inst->alg.chunksize = alg->cra_blocksize; + + inst->alg.encrypt = crypto_xctr_crypt; + inst->alg.decrypt = crypto_xctr_crypt; + + err = skcipher_register_instance(tmpl, inst); + if (err) { +out_free_inst: + inst->free(inst); + } + + return err; +} + +static struct crypto_template crypto_xctr_tmpl = { + .name = "xctr", + .create = crypto_xctr_create, + .module = THIS_MODULE, +}; + +static int __init crypto_xctr_module_init(void) +{ + return crypto_register_template(&crypto_xctr_tmpl); +} + +static void __exit crypto_xctr_module_exit(void) +{ + crypto_unregister_template(&crypto_xctr_tmpl); +} + +subsys_initcall(crypto_xctr_module_init); +module_exit(crypto_xctr_module_exit); + +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("XCTR block cipher mode of operation"); +MODULE_ALIAS_CRYPTO("xctr"); +MODULE_IMPORT_NS(CRYPTO_INTERNAL); |