diff options
Diffstat (limited to 'crypto/hctr2.c')
| -rw-r--r-- | crypto/hctr2.c | 581 |
1 files changed, 581 insertions, 0 deletions
diff --git a/crypto/hctr2.c b/crypto/hctr2.c new file mode 100644 index 000000000..7d00a3bcb --- /dev/null +++ b/crypto/hctr2.c @@ -0,0 +1,581 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * HCTR2 length-preserving encryption mode + * + * Copyright 2021 Google LLC + */ + + +/* + * HCTR2 is a length-preserving encryption mode that is efficient on + * processors with instructions to accelerate AES and carryless + * multiplication, e.g. x86 processors with AES-NI and CLMUL, and ARM + * processors with the ARMv8 crypto extensions. + * + * For more details, see the paper: "Length-preserving encryption with HCTR2" + * (https://eprint.iacr.org/2021/1441.pdf) + */ + +#include <crypto/internal/cipher.h> +#include <crypto/internal/hash.h> +#include <crypto/internal/skcipher.h> +#include <crypto/polyval.h> +#include <crypto/scatterwalk.h> +#include <linux/module.h> + +#define BLOCKCIPHER_BLOCK_SIZE 16 + +/* + * The specification allows variable-length tweaks, but Linux's crypto API + * currently only allows algorithms to support a single length. The "natural" + * tweak length for HCTR2 is 16, since that fits into one POLYVAL block for + * the best performance. But longer tweaks are useful for fscrypt, to avoid + * needing to derive per-file keys. So instead we use two blocks, or 32 bytes. + */ +#define TWEAK_SIZE 32 + +struct hctr2_instance_ctx { + struct crypto_cipher_spawn blockcipher_spawn; + struct crypto_skcipher_spawn xctr_spawn; + struct crypto_shash_spawn polyval_spawn; +}; + +struct hctr2_tfm_ctx { + struct crypto_cipher *blockcipher; + struct crypto_skcipher *xctr; + struct crypto_shash *polyval; + u8 L[BLOCKCIPHER_BLOCK_SIZE]; + int hashed_tweak_offset; + /* + * This struct is allocated with extra space for two exported hash + * states. Since the hash state size is not known at compile-time, we + * can't add these to the struct directly. + * + * hashed_tweaklen_divisible; + * hashed_tweaklen_remainder; + */ +}; + +struct hctr2_request_ctx { + u8 first_block[BLOCKCIPHER_BLOCK_SIZE]; + u8 xctr_iv[BLOCKCIPHER_BLOCK_SIZE]; + struct scatterlist *bulk_part_dst; + struct scatterlist *bulk_part_src; + struct scatterlist sg_src[2]; + struct scatterlist sg_dst[2]; + /* + * Sub-request sizes are unknown at compile-time, so they need to go + * after the members with known sizes. + */ + union { + struct shash_desc hash_desc; + struct skcipher_request xctr_req; + } u; + /* + * This struct is allocated with extra space for one exported hash + * state. Since the hash state size is not known at compile-time, we + * can't add it to the struct directly. + * + * hashed_tweak; + */ +}; + +static inline u8 *hctr2_hashed_tweaklen(const struct hctr2_tfm_ctx *tctx, + bool has_remainder) +{ + u8 *p = (u8 *)tctx + sizeof(*tctx); + + if (has_remainder) /* For messages not a multiple of block length */ + p += crypto_shash_statesize(tctx->polyval); + return p; +} + +static inline u8 *hctr2_hashed_tweak(const struct hctr2_tfm_ctx *tctx, + struct hctr2_request_ctx *rctx) +{ + return (u8 *)rctx + tctx->hashed_tweak_offset; +} + +/* + * The input data for each HCTR2 hash step begins with a 16-byte block that + * contains the tweak length and a flag that indicates whether the input is evenly + * divisible into blocks. Since this implementation only supports one tweak + * length, we precompute the two hash states resulting from hashing the two + * possible values of this initial block. This reduces by one block the amount of + * data that needs to be hashed for each encryption/decryption + * + * These precomputed hashes are stored in hctr2_tfm_ctx. + */ +static int hctr2_hash_tweaklen(struct hctr2_tfm_ctx *tctx, bool has_remainder) +{ + SHASH_DESC_ON_STACK(shash, tfm->polyval); + __le64 tweak_length_block[2]; + int err; + + shash->tfm = tctx->polyval; + memset(tweak_length_block, 0, sizeof(tweak_length_block)); + + tweak_length_block[0] = cpu_to_le64(TWEAK_SIZE * 8 * 2 + 2 + has_remainder); + err = crypto_shash_init(shash); + if (err) + return err; + err = crypto_shash_update(shash, (u8 *)tweak_length_block, + POLYVAL_BLOCK_SIZE); + if (err) + return err; + return crypto_shash_export(shash, hctr2_hashed_tweaklen(tctx, has_remainder)); +} + +static int hctr2_setkey(struct crypto_skcipher *tfm, const u8 *key, + unsigned int keylen) +{ + struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + u8 hbar[BLOCKCIPHER_BLOCK_SIZE]; + int err; + + crypto_cipher_clear_flags(tctx->blockcipher, CRYPTO_TFM_REQ_MASK); + crypto_cipher_set_flags(tctx->blockcipher, + crypto_skcipher_get_flags(tfm) & + CRYPTO_TFM_REQ_MASK); + err = crypto_cipher_setkey(tctx->blockcipher, key, keylen); + if (err) + return err; + + crypto_skcipher_clear_flags(tctx->xctr, CRYPTO_TFM_REQ_MASK); + crypto_skcipher_set_flags(tctx->xctr, + crypto_skcipher_get_flags(tfm) & + CRYPTO_TFM_REQ_MASK); + err = crypto_skcipher_setkey(tctx->xctr, key, keylen); + if (err) + return err; + + memset(hbar, 0, sizeof(hbar)); + crypto_cipher_encrypt_one(tctx->blockcipher, hbar, hbar); + + memset(tctx->L, 0, sizeof(tctx->L)); + tctx->L[0] = 0x01; + crypto_cipher_encrypt_one(tctx->blockcipher, tctx->L, tctx->L); + + crypto_shash_clear_flags(tctx->polyval, CRYPTO_TFM_REQ_MASK); + crypto_shash_set_flags(tctx->polyval, crypto_skcipher_get_flags(tfm) & + CRYPTO_TFM_REQ_MASK); + err = crypto_shash_setkey(tctx->polyval, hbar, BLOCKCIPHER_BLOCK_SIZE); + if (err) + return err; + memzero_explicit(hbar, sizeof(hbar)); + + return hctr2_hash_tweaklen(tctx, true) ?: hctr2_hash_tweaklen(tctx, false); +} + +static int hctr2_hash_tweak(struct skcipher_request *req) +{ + struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); + const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + struct hctr2_request_ctx *rctx = skcipher_request_ctx(req); + struct shash_desc *hash_desc = &rctx->u.hash_desc; + int err; + bool has_remainder = req->cryptlen % POLYVAL_BLOCK_SIZE; + + hash_desc->tfm = tctx->polyval; + err = crypto_shash_import(hash_desc, hctr2_hashed_tweaklen(tctx, has_remainder)); + if (err) + return err; + err = crypto_shash_update(hash_desc, req->iv, TWEAK_SIZE); + if (err) + return err; + + // Store the hashed tweak, since we need it when computing both + // H(T || N) and H(T || V). + return crypto_shash_export(hash_desc, hctr2_hashed_tweak(tctx, rctx)); +} + +static int hctr2_hash_message(struct skcipher_request *req, + struct scatterlist *sgl, + u8 digest[POLYVAL_DIGEST_SIZE]) +{ + static const u8 padding[BLOCKCIPHER_BLOCK_SIZE] = { 0x1 }; + struct hctr2_request_ctx *rctx = skcipher_request_ctx(req); + struct shash_desc *hash_desc = &rctx->u.hash_desc; + const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE; + struct sg_mapping_iter miter; + unsigned int remainder = bulk_len % BLOCKCIPHER_BLOCK_SIZE; + int i; + int err = 0; + int n = 0; + + sg_miter_start(&miter, sgl, sg_nents(sgl), + SG_MITER_FROM_SG | SG_MITER_ATOMIC); + for (i = 0; i < bulk_len; i += n) { + sg_miter_next(&miter); + n = min_t(unsigned int, miter.length, bulk_len - i); + err = crypto_shash_update(hash_desc, miter.addr, n); + if (err) + break; + } + sg_miter_stop(&miter); + + if (err) + return err; + + if (remainder) { + err = crypto_shash_update(hash_desc, padding, + BLOCKCIPHER_BLOCK_SIZE - remainder); + if (err) + return err; + } + return crypto_shash_final(hash_desc, digest); +} + +static int hctr2_finish(struct skcipher_request *req) +{ + struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); + const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + struct hctr2_request_ctx *rctx = skcipher_request_ctx(req); + u8 digest[POLYVAL_DIGEST_SIZE]; + struct shash_desc *hash_desc = &rctx->u.hash_desc; + int err; + + // U = UU ^ H(T || V) + // or M = MM ^ H(T || N) + hash_desc->tfm = tctx->polyval; + err = crypto_shash_import(hash_desc, hctr2_hashed_tweak(tctx, rctx)); + if (err) + return err; + err = hctr2_hash_message(req, rctx->bulk_part_dst, digest); + if (err) + return err; + crypto_xor(rctx->first_block, digest, BLOCKCIPHER_BLOCK_SIZE); + + // Copy U (or M) into dst scatterlist + scatterwalk_map_and_copy(rctx->first_block, req->dst, + 0, BLOCKCIPHER_BLOCK_SIZE, 1); + return 0; +} + +static void hctr2_xctr_done(struct crypto_async_request *areq, + int err) +{ + struct skcipher_request *req = areq->data; + + if (!err) + err = hctr2_finish(req); + + skcipher_request_complete(req, err); +} + +static int hctr2_crypt(struct skcipher_request *req, bool enc) +{ + struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); + const struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + struct hctr2_request_ctx *rctx = skcipher_request_ctx(req); + u8 digest[POLYVAL_DIGEST_SIZE]; + int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE; + int err; + + // Requests must be at least one block + if (req->cryptlen < BLOCKCIPHER_BLOCK_SIZE) + return -EINVAL; + + // Copy M (or U) into a temporary buffer + scatterwalk_map_and_copy(rctx->first_block, req->src, + 0, BLOCKCIPHER_BLOCK_SIZE, 0); + + // Create scatterlists for N and V + rctx->bulk_part_src = scatterwalk_ffwd(rctx->sg_src, req->src, + BLOCKCIPHER_BLOCK_SIZE); + rctx->bulk_part_dst = scatterwalk_ffwd(rctx->sg_dst, req->dst, + BLOCKCIPHER_BLOCK_SIZE); + + // MM = M ^ H(T || N) + // or UU = U ^ H(T || V) + err = hctr2_hash_tweak(req); + if (err) + return err; + err = hctr2_hash_message(req, rctx->bulk_part_src, digest); + if (err) + return err; + crypto_xor(digest, rctx->first_block, BLOCKCIPHER_BLOCK_SIZE); + + // UU = E(MM) + // or MM = D(UU) + if (enc) + crypto_cipher_encrypt_one(tctx->blockcipher, rctx->first_block, + digest); + else + crypto_cipher_decrypt_one(tctx->blockcipher, rctx->first_block, + digest); + + // S = MM ^ UU ^ L + crypto_xor(digest, rctx->first_block, BLOCKCIPHER_BLOCK_SIZE); + crypto_xor_cpy(rctx->xctr_iv, digest, tctx->L, BLOCKCIPHER_BLOCK_SIZE); + + // V = XCTR(S, N) + // or N = XCTR(S, V) + skcipher_request_set_tfm(&rctx->u.xctr_req, tctx->xctr); + skcipher_request_set_crypt(&rctx->u.xctr_req, rctx->bulk_part_src, + rctx->bulk_part_dst, bulk_len, + rctx->xctr_iv); + skcipher_request_set_callback(&rctx->u.xctr_req, + req->base.flags, + hctr2_xctr_done, req); + return crypto_skcipher_encrypt(&rctx->u.xctr_req) ?: + hctr2_finish(req); +} + +static int hctr2_encrypt(struct skcipher_request *req) +{ + return hctr2_crypt(req, true); +} + +static int hctr2_decrypt(struct skcipher_request *req) +{ + return hctr2_crypt(req, false); +} + +static int hctr2_init_tfm(struct crypto_skcipher *tfm) +{ + struct skcipher_instance *inst = skcipher_alg_instance(tfm); + struct hctr2_instance_ctx *ictx = skcipher_instance_ctx(inst); + struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + struct crypto_skcipher *xctr; + struct crypto_cipher *blockcipher; + struct crypto_shash *polyval; + unsigned int subreq_size; + int err; + + xctr = crypto_spawn_skcipher(&ictx->xctr_spawn); + if (IS_ERR(xctr)) + return PTR_ERR(xctr); + + blockcipher = crypto_spawn_cipher(&ictx->blockcipher_spawn); + if (IS_ERR(blockcipher)) { + err = PTR_ERR(blockcipher); + goto err_free_xctr; + } + + polyval = crypto_spawn_shash(&ictx->polyval_spawn); + if (IS_ERR(polyval)) { + err = PTR_ERR(polyval); + goto err_free_blockcipher; + } + + tctx->xctr = xctr; + tctx->blockcipher = blockcipher; + tctx->polyval = polyval; + + BUILD_BUG_ON(offsetofend(struct hctr2_request_ctx, u) != + sizeof(struct hctr2_request_ctx)); + subreq_size = max(sizeof_field(struct hctr2_request_ctx, u.hash_desc) + + crypto_shash_descsize(polyval), + sizeof_field(struct hctr2_request_ctx, u.xctr_req) + + crypto_skcipher_reqsize(xctr)); + + tctx->hashed_tweak_offset = offsetof(struct hctr2_request_ctx, u) + + subreq_size; + crypto_skcipher_set_reqsize(tfm, tctx->hashed_tweak_offset + + crypto_shash_statesize(polyval)); + return 0; + +err_free_blockcipher: + crypto_free_cipher(blockcipher); +err_free_xctr: + crypto_free_skcipher(xctr); + return err; +} + +static void hctr2_exit_tfm(struct crypto_skcipher *tfm) +{ + struct hctr2_tfm_ctx *tctx = crypto_skcipher_ctx(tfm); + + crypto_free_cipher(tctx->blockcipher); + crypto_free_skcipher(tctx->xctr); + crypto_free_shash(tctx->polyval); +} + +static void hctr2_free_instance(struct skcipher_instance *inst) +{ + struct hctr2_instance_ctx *ictx = skcipher_instance_ctx(inst); + + crypto_drop_cipher(&ictx->blockcipher_spawn); + crypto_drop_skcipher(&ictx->xctr_spawn); + crypto_drop_shash(&ictx->polyval_spawn); + kfree(inst); +} + +static int hctr2_create_common(struct crypto_template *tmpl, + struct rtattr **tb, + const char *xctr_name, + const char *polyval_name) +{ + u32 mask; + struct skcipher_instance *inst; + struct hctr2_instance_ctx *ictx; + struct skcipher_alg *xctr_alg; + struct crypto_alg *blockcipher_alg; + struct shash_alg *polyval_alg; + char blockcipher_name[CRYPTO_MAX_ALG_NAME]; + int len; + int err; + + err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask); + if (err) + return err; + + inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL); + if (!inst) + return -ENOMEM; + ictx = skcipher_instance_ctx(inst); + + /* Stream cipher, xctr(block_cipher) */ + err = crypto_grab_skcipher(&ictx->xctr_spawn, + skcipher_crypto_instance(inst), + xctr_name, 0, mask); + if (err) + goto err_free_inst; + xctr_alg = crypto_spawn_skcipher_alg(&ictx->xctr_spawn); + + err = -EINVAL; + if (strncmp(xctr_alg->base.cra_name, "xctr(", 5)) + goto err_free_inst; + len = strscpy(blockcipher_name, xctr_alg->base.cra_name + 5, + sizeof(blockcipher_name)); + if (len < 1) + goto err_free_inst; + if (blockcipher_name[len - 1] != ')') + goto err_free_inst; + blockcipher_name[len - 1] = 0; + + /* Block cipher, e.g. "aes" */ + err = crypto_grab_cipher(&ictx->blockcipher_spawn, + skcipher_crypto_instance(inst), + blockcipher_name, 0, mask); + if (err) + goto err_free_inst; + blockcipher_alg = crypto_spawn_cipher_alg(&ictx->blockcipher_spawn); + + /* Require blocksize of 16 bytes */ + err = -EINVAL; + if (blockcipher_alg->cra_blocksize != BLOCKCIPHER_BLOCK_SIZE) + goto err_free_inst; + + /* Polyval ε-∆U hash function */ + err = crypto_grab_shash(&ictx->polyval_spawn, + skcipher_crypto_instance(inst), + polyval_name, 0, mask); + if (err) + goto err_free_inst; + polyval_alg = crypto_spawn_shash_alg(&ictx->polyval_spawn); + + /* Ensure Polyval is being used */ + err = -EINVAL; + if (strcmp(polyval_alg->base.cra_name, "polyval") != 0) + goto err_free_inst; + + /* Instance fields */ + + err = -ENAMETOOLONG; + if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME, "hctr2(%s)", + blockcipher_alg->cra_name) >= CRYPTO_MAX_ALG_NAME) + goto err_free_inst; + if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME, + "hctr2_base(%s,%s)", + xctr_alg->base.cra_driver_name, + polyval_alg->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME) + goto err_free_inst; + + inst->alg.base.cra_blocksize = BLOCKCIPHER_BLOCK_SIZE; + inst->alg.base.cra_ctxsize = sizeof(struct hctr2_tfm_ctx) + + polyval_alg->statesize * 2; + inst->alg.base.cra_alignmask = xctr_alg->base.cra_alignmask | + polyval_alg->base.cra_alignmask; + /* + * The hash function is called twice, so it is weighted higher than the + * xctr and blockcipher. + */ + inst->alg.base.cra_priority = (2 * xctr_alg->base.cra_priority + + 4 * polyval_alg->base.cra_priority + + blockcipher_alg->cra_priority) / 7; + + inst->alg.setkey = hctr2_setkey; + inst->alg.encrypt = hctr2_encrypt; + inst->alg.decrypt = hctr2_decrypt; + inst->alg.init = hctr2_init_tfm; + inst->alg.exit = hctr2_exit_tfm; + inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(xctr_alg); + inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(xctr_alg); + inst->alg.ivsize = TWEAK_SIZE; + + inst->free = hctr2_free_instance; + + err = skcipher_register_instance(tmpl, inst); + if (err) { +err_free_inst: + hctr2_free_instance(inst); + } + return err; +} + +static int hctr2_create_base(struct crypto_template *tmpl, struct rtattr **tb) +{ + const char *xctr_name; + const char *polyval_name; + + xctr_name = crypto_attr_alg_name(tb[1]); + if (IS_ERR(xctr_name)) + return PTR_ERR(xctr_name); + + polyval_name = crypto_attr_alg_name(tb[2]); + if (IS_ERR(polyval_name)) + return PTR_ERR(polyval_name); + + return hctr2_create_common(tmpl, tb, xctr_name, polyval_name); +} + +static int hctr2_create(struct crypto_template *tmpl, struct rtattr **tb) +{ + const char *blockcipher_name; + char xctr_name[CRYPTO_MAX_ALG_NAME]; + + blockcipher_name = crypto_attr_alg_name(tb[1]); + if (IS_ERR(blockcipher_name)) + return PTR_ERR(blockcipher_name); + + if (snprintf(xctr_name, CRYPTO_MAX_ALG_NAME, "xctr(%s)", + blockcipher_name) >= CRYPTO_MAX_ALG_NAME) + return -ENAMETOOLONG; + + return hctr2_create_common(tmpl, tb, xctr_name, "polyval"); +} + +static struct crypto_template hctr2_tmpls[] = { + { + /* hctr2_base(xctr_name, polyval_name) */ + .name = "hctr2_base", + .create = hctr2_create_base, + .module = THIS_MODULE, + }, { + /* hctr2(blockcipher_name) */ + .name = "hctr2", + .create = hctr2_create, + .module = THIS_MODULE, + } +}; + +static int __init hctr2_module_init(void) +{ + return crypto_register_templates(hctr2_tmpls, ARRAY_SIZE(hctr2_tmpls)); +} + +static void __exit hctr2_module_exit(void) +{ + return crypto_unregister_templates(hctr2_tmpls, + ARRAY_SIZE(hctr2_tmpls)); +} + +subsys_initcall(hctr2_module_init); +module_exit(hctr2_module_exit); + +MODULE_DESCRIPTION("HCTR2 length-preserving encryption mode"); +MODULE_LICENSE("GPL v2"); +MODULE_ALIAS_CRYPTO("hctr2"); +MODULE_IMPORT_NS(CRYPTO_INTERNAL); |