/* * CTS: Cipher Text Stealing mode * * COPYRIGHT (c) 2008 * The Regents of the University of Michigan * ALL RIGHTS RESERVED * * Permission is granted to use, copy, create derivative works * and redistribute this software and such derivative works * for any purpose, so long as the name of The University of * Michigan is not used in any advertising or publicity * pertaining to the use of distribution of this software * without specific, written prior authorization. If the * above copyright notice or any other identification of the * University of Michigan is included in any copy of any * portion of this software, then the disclaimer below must * also be included. * * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF * SUCH DAMAGES. */ /* Derived from various: * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au> */ /* * This is the Cipher Text Stealing mode as described by * Section 8 of rfc2040 and referenced by rfc3962. * rfc3962 includes errata information in its Appendix A. */ #include <crypto/algapi.h> #include <linux/err.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/log2.h> #include <linux/module.h> #include <linux/scatterlist.h> #include <crypto/scatterwalk.h> #include <linux/slab.h> struct crypto_cts_ctx { struct crypto_blkcipher *child; }; static int crypto_cts_setkey(struct crypto_tfm *parent, const u8 *key, unsigned int keylen) { struct crypto_cts_ctx *ctx = crypto_tfm_ctx(parent); struct crypto_blkcipher *child = ctx->child; int err; crypto_blkcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); crypto_blkcipher_set_flags(child, crypto_tfm_get_flags(parent) & CRYPTO_TFM_REQ_MASK); err = crypto_blkcipher_setkey(child, key, keylen); crypto_tfm_set_flags(parent, crypto_blkcipher_get_flags(child) & CRYPTO_TFM_RES_MASK); return err; } static int cts_cbc_encrypt(struct crypto_cts_ctx *ctx, struct blkcipher_desc *desc, struct scatterlist *dst, struct scatterlist *src, unsigned int offset, unsigned int nbytes) { int bsize = crypto_blkcipher_blocksize(desc->tfm); u8 tmp[bsize], tmp2[bsize]; struct blkcipher_desc lcldesc; struct scatterlist sgsrc[1], sgdst[1]; int lastn = nbytes - bsize; u8 iv[bsize]; u8 s[bsize * 2], d[bsize * 2]; int err; if (lastn < 0) return -EINVAL; sg_init_table(sgsrc, 1); sg_init_table(sgdst, 1); memset(s, 0, sizeof(s)); scatterwalk_map_and_copy(s, src, offset, nbytes, 0); memcpy(iv, desc->info, bsize); lcldesc.tfm = ctx->child; lcldesc.info = iv; lcldesc.flags = desc->flags; sg_set_buf(&sgsrc[0], s, bsize); sg_set_buf(&sgdst[0], tmp, bsize); err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize); memcpy(d + bsize, tmp, lastn); lcldesc.info = tmp; sg_set_buf(&sgsrc[0], s + bsize, bsize); sg_set_buf(&sgdst[0], tmp2, bsize); err = crypto_blkcipher_encrypt_iv(&lcldesc, sgdst, sgsrc, bsize); memcpy(d, tmp2, bsize); scatterwalk_map_and_copy(d, dst, offset, nbytes, 1); memcpy(desc->info, tmp2, bsize); return err; } static int crypto_cts_encrypt(struct blkcipher_desc *desc, struct scatterlist *dst, struct scatterlist *src, unsigned int nbytes) { struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm); int bsize = crypto_blkcipher_blocksize(desc->tfm); int tot_blocks = (nbytes + bsize - 1) / bsize; int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0; struct blkcipher_desc lcldesc; int err; lcldesc.tfm = ctx->child; lcldesc.info = desc->info; lcldesc.flags = desc->flags; if (tot_blocks == 1) { err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, bsize); } else if (nbytes <= bsize * 2) { err = cts_cbc_encrypt(ctx, desc, dst, src, 0, nbytes); } else { /* do normal function for tot_blocks - 2 */ err = crypto_blkcipher_encrypt_iv(&lcldesc, dst, src, cbc_blocks * bsize); if (err == 0) { /* do cts for final two blocks */ err = cts_cbc_encrypt(ctx, desc, dst, src, cbc_blocks * bsize, nbytes - (cbc_blocks * bsize)); } } return err; } static int cts_cbc_decrypt(struct crypto_cts_ctx *ctx, struct blkcipher_desc *desc, struct scatterlist *dst, struct scatterlist *src, unsigned int offset, unsigned int nbytes) { int bsize = crypto_blkcipher_blocksize(desc->tfm); u8 tmp[bsize]; struct blkcipher_desc lcldesc; struct scatterlist sgsrc[1], sgdst[1]; int lastn = nbytes - bsize; u8 iv[bsize]; u8 s[bsize * 2], d[bsize * 2]; int err; if (lastn < 0) return -EINVAL; sg_init_table(sgsrc, 1); sg_init_table(sgdst, 1); scatterwalk_map_and_copy(s, src, offset, nbytes, 0); lcldesc.tfm = ctx->child; lcldesc.info = iv; lcldesc.flags = desc->flags; /* 1. Decrypt Cn-1 (s) to create Dn (tmp)*/ memset(iv, 0, sizeof(iv)); sg_set_buf(&sgsrc[0], s, bsize); sg_set_buf(&sgdst[0], tmp, bsize); err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize); if (err) return err; /* 2. Pad Cn with zeros at the end to create C of length BB */ memset(iv, 0, sizeof(iv)); memcpy(iv, s + bsize, lastn); /* 3. Exclusive-or Dn (tmp) with C (iv) to create Xn (tmp) */ crypto_xor(tmp, iv, bsize); /* 4. Select the first Ln bytes of Xn (tmp) to create Pn */ memcpy(d + bsize, tmp, lastn); /* 5. Append the tail (BB - Ln) bytes of Xn (tmp) to Cn to create En */ memcpy(s + bsize + lastn, tmp + lastn, bsize - lastn); /* 6. Decrypt En to create Pn-1 */ memzero_explicit(iv, sizeof(iv)); sg_set_buf(&sgsrc[0], s + bsize, bsize); sg_set_buf(&sgdst[0], d, bsize); err = crypto_blkcipher_decrypt_iv(&lcldesc, sgdst, sgsrc, bsize); /* XOR with previous block */ crypto_xor(d, desc->info, bsize); scatterwalk_map_and_copy(d, dst, offset, nbytes, 1); memcpy(desc->info, s, bsize); return err; } static int crypto_cts_decrypt(struct blkcipher_desc *desc, struct scatterlist *dst, struct scatterlist *src, unsigned int nbytes) { struct crypto_cts_ctx *ctx = crypto_blkcipher_ctx(desc->tfm); int bsize = crypto_blkcipher_blocksize(desc->tfm); int tot_blocks = (nbytes + bsize - 1) / bsize; int cbc_blocks = tot_blocks > 2 ? tot_blocks - 2 : 0; struct blkcipher_desc lcldesc; int err; lcldesc.tfm = ctx->child; lcldesc.info = desc->info; lcldesc.flags = desc->flags; if (tot_blocks == 1) { err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, bsize); } else if (nbytes <= bsize * 2) { err = cts_cbc_decrypt(ctx, desc, dst, src, 0, nbytes); } else { /* do normal function for tot_blocks - 2 */ err = crypto_blkcipher_decrypt_iv(&lcldesc, dst, src, cbc_blocks * bsize); if (err == 0) { /* do cts for final two blocks */ err = cts_cbc_decrypt(ctx, desc, dst, src, cbc_blocks * bsize, nbytes - (cbc_blocks * bsize)); } } return err; } static int crypto_cts_init_tfm(struct crypto_tfm *tfm) { struct crypto_instance *inst = (void *)tfm->__crt_alg; struct crypto_spawn *spawn = crypto_instance_ctx(inst); struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm); struct crypto_blkcipher *cipher; cipher = crypto_spawn_blkcipher(spawn); if (IS_ERR(cipher)) return PTR_ERR(cipher); ctx->child = cipher; return 0; } static void crypto_cts_exit_tfm(struct crypto_tfm *tfm) { struct crypto_cts_ctx *ctx = crypto_tfm_ctx(tfm); crypto_free_blkcipher(ctx->child); } static struct crypto_instance *crypto_cts_alloc(struct rtattr **tb) { struct crypto_instance *inst; struct crypto_alg *alg; int err; err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER); if (err) return ERR_PTR(err); alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_BLKCIPHER, CRYPTO_ALG_TYPE_MASK); if (IS_ERR(alg)) return ERR_CAST(alg); inst = ERR_PTR(-EINVAL); if (!is_power_of_2(alg->cra_blocksize)) goto out_put_alg; if (strncmp(alg->cra_name, "cbc(", 4)) goto out_put_alg; inst = crypto_alloc_instance("cts", alg); if (IS_ERR(inst)) goto out_put_alg; inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER; inst->alg.cra_priority = alg->cra_priority; inst->alg.cra_blocksize = alg->cra_blocksize; inst->alg.cra_alignmask = alg->cra_alignmask; inst->alg.cra_type = &crypto_blkcipher_type; /* We access the data as u32s when xoring. */ inst->alg.cra_alignmask |= __alignof__(u32) - 1; inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize; inst->alg.cra_blkcipher.min_keysize = alg->cra_blkcipher.min_keysize; inst->alg.cra_blkcipher.max_keysize = alg->cra_blkcipher.max_keysize; inst->alg.cra_ctxsize = sizeof(struct crypto_cts_ctx); inst->alg.cra_init = crypto_cts_init_tfm; inst->alg.cra_exit = crypto_cts_exit_tfm; inst->alg.cra_blkcipher.setkey = crypto_cts_setkey; inst->alg.cra_blkcipher.encrypt = crypto_cts_encrypt; inst->alg.cra_blkcipher.decrypt = crypto_cts_decrypt; out_put_alg: crypto_mod_put(alg); return inst; } static void crypto_cts_free(struct crypto_instance *inst) { crypto_drop_spawn(crypto_instance_ctx(inst)); kfree(inst); } static struct crypto_template crypto_cts_tmpl = { .name = "cts", .alloc = crypto_cts_alloc, .free = crypto_cts_free, .module = THIS_MODULE, }; static int __init crypto_cts_module_init(void) { return crypto_register_template(&crypto_cts_tmpl); } static void __exit crypto_cts_module_exit(void) { crypto_unregister_template(&crypto_cts_tmpl); } module_init(crypto_cts_module_init); module_exit(crypto_cts_module_exit); MODULE_LICENSE("Dual BSD/GPL"); MODULE_DESCRIPTION("CTS-CBC CipherText Stealing for CBC"); MODULE_ALIAS_CRYPTO("cts");