the-tree/crypto/xctr.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * XCTR: XOR Counter mode - Adapted from ctr.c
0004  *
0005  * (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com>
0006  * Copyright 2021 Google LLC
0007  */
0008
0009 /*
0010  * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is
0011  * closely related to the CTR mode of operation; the main difference is that CTR
0012  * generates the keystream using E(CTR + IV) whereas XCTR generates the
0013  * keystream using E(CTR ^ IV). This allows implementations to avoid dealing
0014  * with multi-limb integers (as is required in CTR mode). XCTR is also specified
0015  * using little-endian arithmetic which makes it slightly faster on LE machines.
0016  *
0017  * See the HCTR2 paper for more details:
0018  *  Length-preserving encryption with HCTR2
0019  *      (https://eprint.iacr.org/2021/1441.pdf)
0020  */
0021
0022 #include <crypto/algapi.h>
0023 #include <crypto/internal/cipher.h>
0024 #include <crypto/internal/skcipher.h>
0025 #include <linux/err.h>
0026 #include <linux/init.h>
0027 #include <linux/kernel.h>
0028 #include <linux/module.h>
0029 #include <linux/slab.h>
0030
0031 /* For now this implementation is limited to 16-byte blocks for simplicity */
0032 #define XCTR_BLOCKSIZE 16
0033
0034 static void crypto_xctr_crypt_final(struct skcipher_walk *walk,
0035                    struct crypto_cipher *tfm, u32 byte_ctr)
0036 {
0037     u8 keystream[XCTR_BLOCKSIZE];
0038     const u8 *src = walk->src.virt.addr;
0039     u8 *dst = walk->dst.virt.addr;
0040     unsigned int nbytes = walk->nbytes;
0041     __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
0042
0043     crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0044     crypto_cipher_encrypt_one(tfm, keystream, walk->iv);
0045     crypto_xor_cpy(dst, keystream, src, nbytes);
0046     crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0047 }
0048
0049 static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,
0050                     struct crypto_cipher *tfm, u32 byte_ctr)
0051 {
0052     void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
0053            crypto_cipher_alg(tfm)->cia_encrypt;
0054     const u8 *src = walk->src.virt.addr;
0055     u8 *dst = walk->dst.virt.addr;
0056     unsigned int nbytes = walk->nbytes;
0057     __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
0058
0059     do {
0060         crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0061         fn(crypto_cipher_tfm(tfm), dst, walk->iv);
0062         crypto_xor(dst, src, XCTR_BLOCKSIZE);
0063         crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0064
0065         le32_add_cpu(&ctr32, 1);
0066
0067         src += XCTR_BLOCKSIZE;
0068         dst += XCTR_BLOCKSIZE;
0069     } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
0070
0071     return nbytes;
0072 }
0073
0074 static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,
0075                     struct crypto_cipher *tfm, u32 byte_ctr)
0076 {
0077     void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
0078            crypto_cipher_alg(tfm)->cia_encrypt;
0079     unsigned long alignmask = crypto_cipher_alignmask(tfm);
0080     unsigned int nbytes = walk->nbytes;
0081     u8 *data = walk->src.virt.addr;
0082     u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
0083     u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
0084     __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
0085
0086     do {
0087         crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0088         fn(crypto_cipher_tfm(tfm), keystream, walk->iv);
0089         crypto_xor(data, keystream, XCTR_BLOCKSIZE);
0090         crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
0091
0092         le32_add_cpu(&ctr32, 1);
0093
0094         data += XCTR_BLOCKSIZE;
0095     } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
0096
0097     return nbytes;
0098 }
0099
0100 static int crypto_xctr_crypt(struct skcipher_request *req)
0101 {
0102     struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
0103     struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
0104     struct skcipher_walk walk;
0105     unsigned int nbytes;
0106     int err;
0107     u32 byte_ctr = 0;
0108
0109     err = skcipher_walk_virt(&walk, req, false);
0110
0111     while (walk.nbytes >= XCTR_BLOCKSIZE) {
0112         if (walk.src.virt.addr == walk.dst.virt.addr)
0113             nbytes = crypto_xctr_crypt_inplace(&walk, cipher,
0114                                byte_ctr);
0115         else
0116             nbytes = crypto_xctr_crypt_segment(&walk, cipher,
0117                                byte_ctr);
0118
0119         byte_ctr += walk.nbytes - nbytes;
0120         err = skcipher_walk_done(&walk, nbytes);
0121     }
0122
0123     if (walk.nbytes) {
0124         crypto_xctr_crypt_final(&walk, cipher, byte_ctr);
0125         err = skcipher_walk_done(&walk, 0);
0126     }
0127
0128     return err;
0129 }
0130
0131 static int crypto_xctr_create(struct crypto_template *tmpl, struct rtattr **tb)
0132 {
0133     struct skcipher_instance *inst;
0134     struct crypto_alg *alg;
0135     int err;
0136
0137     inst = skcipher_alloc_instance_simple(tmpl, tb);
0138     if (IS_ERR(inst))
0139         return PTR_ERR(inst);
0140
0141     alg = skcipher_ialg_simple(inst);
0142
0143     /* Block size must be 16 bytes. */
0144     err = -EINVAL;
0145     if (alg->cra_blocksize != XCTR_BLOCKSIZE)
0146         goto out_free_inst;
0147
0148     /* XCTR mode is a stream cipher. */
0149     inst->alg.base.cra_blocksize = 1;
0150
0151     /*
0152      * To simplify the implementation, configure the skcipher walk to only
0153      * give a partial block at the very end, never earlier.
0154      */
0155     inst->alg.chunksize = alg->cra_blocksize;
0156
0157     inst->alg.encrypt = crypto_xctr_crypt;
0158     inst->alg.decrypt = crypto_xctr_crypt;
0159
0160     err = skcipher_register_instance(tmpl, inst);
0161     if (err) {
0162 out_free_inst:
0163         inst->free(inst);
0164     }
0165
0166     return err;
0167 }
0168
0169 static struct crypto_template crypto_xctr_tmpl = {
0170     .name = "xctr",
0171     .create = crypto_xctr_create,
0172     .module = THIS_MODULE,
0173 };
0174
0175 static int __init crypto_xctr_module_init(void)
0176 {
0177     return crypto_register_template(&crypto_xctr_tmpl);
0178 }
0179
0180 static void __exit crypto_xctr_module_exit(void)
0181 {
0182     crypto_unregister_template(&crypto_xctr_tmpl);
0183 }
0184
0185 subsys_initcall(crypto_xctr_module_init);
0186 module_exit(crypto_xctr_module_exit);
0187
0188 MODULE_LICENSE("GPL");
0189 MODULE_DESCRIPTION("XCTR block cipher mode of operation");
0190 MODULE_ALIAS_CRYPTO("xctr");
0191 MODULE_IMPORT_NS(CRYPTO_INTERNAL);