/* * 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/internal/skcipher.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_skcipher *child; }; struct crypto_cts_reqctx { struct scatterlist sg[2]; unsigned offset; struct skcipher_request subreq; }; static inline u8 *crypto_cts_reqctx_space(struct skcipher_request *req) { struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); struct crypto_skcipher *child = ctx->child; return PTR_ALIGN((u8 *)(rctx + 1) + crypto_skcipher_reqsize(child), crypto_skcipher_alignmask(tfm) + 1); } static int crypto_cts_setkey(struct crypto_skcipher *parent, const u8 *key, unsigned int keylen) { struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(parent); struct crypto_skcipher *child = ctx->child; int err; crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK); crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) & CRYPTO_TFM_REQ_MASK); err = crypto_skcipher_setkey(child, key, keylen); crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) & CRYPTO_TFM_RES_MASK); return err; } static void cts_cbc_crypt_done(struct crypto_async_request *areq, int err) { struct skcipher_request *req = areq->data; if (err == -EINPROGRESS) return; skcipher_request_complete(req, err); } static int cts_cbc_encrypt(struct skcipher_request *req) { struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32)))); struct scatterlist *sg; unsigned int offset; int lastn; offset = rctx->offset; lastn = req->cryptlen - offset; sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); memset(d, 0, bsize); scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); memzero_explicit(d, sizeof(d)); skcipher_request_set_callback(subreq, req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG, cts_cbc_crypt_done, req); skcipher_request_set_crypt(subreq, sg, sg, bsize, req->iv); return crypto_skcipher_encrypt(subreq); } static void crypto_cts_encrypt_done(struct crypto_async_request *areq, int err) { struct skcipher_request *req = areq->data; if (err) goto out; err = cts_cbc_encrypt(req); if (err == -EINPROGRESS || (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) return; out: skcipher_request_complete(req, err); } static int crypto_cts_encrypt(struct skcipher_request *req) { struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); unsigned int nbytes = req->cryptlen; int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; unsigned int offset; skcipher_request_set_tfm(subreq, ctx->child); if (cbc_blocks <= 0) { skcipher_request_set_callback(subreq, req->base.flags, req->base.complete, req->base.data); skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, req->iv); return crypto_skcipher_encrypt(subreq); } offset = cbc_blocks * bsize; rctx->offset = offset; skcipher_request_set_callback(subreq, req->base.flags, crypto_cts_encrypt_done, req); skcipher_request_set_crypt(subreq, req->src, req->dst, offset, req->iv); return crypto_skcipher_encrypt(subreq) ?: cts_cbc_encrypt(req); } static int cts_cbc_decrypt(struct skcipher_request *req) { struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); u8 d[bsize * 2] __attribute__ ((aligned(__alignof__(u32)))); struct scatterlist *sg; unsigned int offset; u8 *space; int lastn; offset = rctx->offset; lastn = req->cryptlen - offset; sg = scatterwalk_ffwd(rctx->sg, req->dst, offset - bsize); /* 1. Decrypt Cn-1 (s) to create Dn */ scatterwalk_map_and_copy(d + bsize, sg, 0, bsize, 0); space = crypto_cts_reqctx_space(req); crypto_xor(d + bsize, space, bsize); /* 2. Pad Cn with zeros at the end to create C of length BB */ memset(d, 0, bsize); scatterwalk_map_and_copy(d, req->src, offset, lastn, 0); /* 3. Exclusive-or Dn with C to create Xn */ /* 4. Select the first Ln bytes of Xn to create Pn */ crypto_xor(d + bsize, d, lastn); /* 5. Append the tail (BB - Ln) bytes of Xn to Cn to create En */ memcpy(d + lastn, d + bsize + lastn, bsize - lastn); /* 6. Decrypt En to create Pn-1 */ scatterwalk_map_and_copy(d, sg, 0, bsize + lastn, 1); memzero_explicit(d, sizeof(d)); skcipher_request_set_callback(subreq, req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG, cts_cbc_crypt_done, req); skcipher_request_set_crypt(subreq, sg, sg, bsize, space); return crypto_skcipher_decrypt(subreq); } static void crypto_cts_decrypt_done(struct crypto_async_request *areq, int err) { struct skcipher_request *req = areq->data; if (err) goto out; err = cts_cbc_decrypt(req); if (err == -EINPROGRESS || (err == -EBUSY && req->base.flags & CRYPTO_TFM_REQ_MAY_BACKLOG)) return; out: skcipher_request_complete(req, err); } static int crypto_cts_decrypt(struct skcipher_request *req) { struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); struct crypto_cts_reqctx *rctx = skcipher_request_ctx(req); struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); struct skcipher_request *subreq = &rctx->subreq; int bsize = crypto_skcipher_blocksize(tfm); unsigned int nbytes = req->cryptlen; int cbc_blocks = (nbytes + bsize - 1) / bsize - 1; unsigned int offset; u8 *space; skcipher_request_set_tfm(subreq, ctx->child); if (cbc_blocks <= 0) { skcipher_request_set_callback(subreq, req->base.flags, req->base.complete, req->base.data); skcipher_request_set_crypt(subreq, req->src, req->dst, nbytes, req->iv); return crypto_skcipher_decrypt(subreq); } skcipher_request_set_callback(subreq, req->base.flags, crypto_cts_decrypt_done, req); space = crypto_cts_reqctx_space(req); offset = cbc_blocks * bsize; rctx->offset = offset; if (cbc_blocks <= 1) memcpy(space, req->iv, bsize); else scatterwalk_map_and_copy(space, req->src, offset - 2 * bsize, bsize, 0); skcipher_request_set_crypt(subreq, req->src, req->dst, offset, req->iv); return crypto_skcipher_decrypt(subreq) ?: cts_cbc_decrypt(req); } static int crypto_cts_init_tfm(struct crypto_skcipher *tfm) { struct skcipher_instance *inst = skcipher_alg_instance(tfm); struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst); struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); struct crypto_skcipher *cipher; unsigned reqsize; unsigned bsize; unsigned align; cipher = crypto_spawn_skcipher(spawn); if (IS_ERR(cipher)) return PTR_ERR(cipher); ctx->child = cipher; align = crypto_skcipher_alignmask(tfm); bsize = crypto_skcipher_blocksize(cipher); reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) + crypto_skcipher_reqsize(cipher), crypto_tfm_ctx_alignment()) + (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize; crypto_skcipher_set_reqsize(tfm, reqsize); return 0; } static void crypto_cts_exit_tfm(struct crypto_skcipher *tfm) { struct crypto_cts_ctx *ctx = crypto_skcipher_ctx(tfm); crypto_free_skcipher(ctx->child); } static void crypto_cts_free(struct skcipher_instance *inst) { crypto_drop_skcipher(skcipher_instance_ctx(inst)); kfree(inst); } static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb) { struct crypto_skcipher_spawn *spawn; struct skcipher_instance *inst; struct crypto_attr_type *algt; struct skcipher_alg *alg; const char *cipher_name; int err; algt = crypto_get_attr_type(tb); if (IS_ERR(algt)) return PTR_ERR(algt); if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask) return -EINVAL; cipher_name = crypto_attr_alg_name(tb[1]); if (IS_ERR(cipher_name)) return PTR_ERR(cipher_name); inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL); if (!inst) return -ENOMEM; spawn = skcipher_instance_ctx(inst); crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst)); err = crypto_grab_skcipher(spawn, cipher_name, 0, crypto_requires_sync(algt->type, algt->mask)); if (err) goto err_free_inst; alg = crypto_spawn_skcipher_alg(spawn); err = -EINVAL; if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize) goto err_drop_spawn; if (strncmp(alg->base.cra_name, "cbc(", 4)) goto err_drop_spawn; err = crypto_inst_setname(skcipher_crypto_instance(inst), "cts", &alg->base); if (err) goto err_drop_spawn; inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC; inst->alg.base.cra_priority = alg->base.cra_priority; inst->alg.base.cra_blocksize = alg->base.cra_blocksize; inst->alg.base.cra_alignmask = alg->base.cra_alignmask; /* We access the data as u32s when xoring. */ inst->alg.base.cra_alignmask |= __alignof__(u32) - 1; inst->alg.ivsize = alg->base.cra_blocksize; inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg); inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg); inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg); inst->alg.base.cra_ctxsize = sizeof(struct crypto_cts_ctx); inst->alg.init = crypto_cts_init_tfm; inst->alg.exit = crypto_cts_exit_tfm; inst->alg.setkey = crypto_cts_setkey; inst->alg.encrypt = crypto_cts_encrypt; inst->alg.decrypt = crypto_cts_decrypt; inst->free = crypto_cts_free; err = skcipher_register_instance(tmpl, inst); if (err) goto err_drop_spawn; out: return err; err_drop_spawn: crypto_drop_skcipher(spawn); err_free_inst: kfree(inst); goto out; } static struct crypto_template crypto_cts_tmpl = { .name = "cts", .create = crypto_cts_create, .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");