echainiv.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * echainiv: Encrypted Chain IV Generator
  4 *
  5 * This generator generates an IV based on a sequence number by multiplying
  6 * it with a salt and then encrypting it with the same key as used to encrypt
  7 * the plain text.  This algorithm requires that the block size be equal
  8 * to the IV size.  It is mainly useful for CBC.
  9 *
 10 * This generator can only be used by algorithms where authentication
 11 * is performed after encryption (i.e., authenc).
 12 *
 13 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
 14 */
 15
 16#include <crypto/internal/geniv.h>
 17#include <crypto/scatterwalk.h>
 18#include <crypto/skcipher.h>
 19#include <linux/err.h>
 20#include <linux/init.h>
 21#include <linux/kernel.h>
 22#include <linux/module.h>
 23#include <linux/slab.h>
 24#include <linux/string.h>
 25
 26static int echainiv_encrypt(struct aead_request *req)
 27{
 28	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
 29	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
 30	struct aead_request *subreq = aead_request_ctx(req);
 31	__be64 nseqno;
 32	u64 seqno;
 33	u8 *info;
 34	unsigned int ivsize = crypto_aead_ivsize(geniv);
 35
 36	if (req->cryptlen < ivsize)
 37		return -EINVAL;
 38
 39	aead_request_set_tfm(subreq, ctx->child);
 40
 41	info = req->iv;
 42
 43	if (req->src != req->dst)
 44		memcpy_sglist(req->dst, req->src,
 45			      req->assoclen + req->cryptlen);
 46
 47	aead_request_set_callback(subreq, req->base.flags,
 48				  req->base.complete, req->base.data);
 49	aead_request_set_crypt(subreq, req->dst, req->dst,
 50			       req->cryptlen, info);
 51	aead_request_set_ad(subreq, req->assoclen);
 52
 53	memcpy(&nseqno, info + ivsize - 8, 8);
 54	seqno = be64_to_cpu(nseqno);
 55	memset(info, 0, ivsize);
 56
 57	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
 58
 59	do {
 60		u64 a;
 61
 62		memcpy(&a, ctx->salt + ivsize - 8, 8);
 63
 64		a |= 1;
 65		a *= seqno;
 66
 67		memcpy(info + ivsize - 8, &a, 8);
 68	} while ((ivsize -= 8));
 69
 70	return crypto_aead_encrypt(subreq);
 71}
 72
 73static int echainiv_decrypt(struct aead_request *req)
 74{
 75	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
 76	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
 77	struct aead_request *subreq = aead_request_ctx(req);
 78	crypto_completion_t compl;
 79	void *data;
 80	unsigned int ivsize = crypto_aead_ivsize(geniv);
 81
 82	if (req->cryptlen < ivsize)
 83		return -EINVAL;
 84
 85	aead_request_set_tfm(subreq, ctx->child);
 86
 87	compl = req->base.complete;
 88	data = req->base.data;
 89
 90	aead_request_set_callback(subreq, req->base.flags, compl, data);
 91	aead_request_set_crypt(subreq, req->src, req->dst,
 92			       req->cryptlen - ivsize, req->iv);
 93	aead_request_set_ad(subreq, req->assoclen + ivsize);
 94
 95	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);
 96
 97	return crypto_aead_decrypt(subreq);
 98}
 99
100static int echainiv_aead_create(struct crypto_template *tmpl,
101				struct rtattr **tb)
102{
103	struct aead_instance *inst;
104	int err;
105
106	inst = aead_geniv_alloc(tmpl, tb);
107
108	if (IS_ERR(inst))
109		return PTR_ERR(inst);
110
111	err = -EINVAL;
112	if (inst->alg.ivsize & (sizeof(u64) - 1) || !inst->alg.ivsize)
113		goto free_inst;
114
115	inst->alg.encrypt = echainiv_encrypt;
116	inst->alg.decrypt = echainiv_decrypt;
117
118	inst->alg.init = aead_init_geniv;
119	inst->alg.exit = aead_exit_geniv;
120
121	inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);
122	inst->alg.base.cra_ctxsize += inst->alg.ivsize;
123
124	err = aead_register_instance(tmpl, inst);
125	if (err) {
126free_inst:
127		inst->free(inst);
128	}
129	return err;
130}
131
132static struct crypto_template echainiv_tmpl = {
133	.name = "echainiv",
134	.create = echainiv_aead_create,
135	.module = THIS_MODULE,
136};
137
138static int __init echainiv_module_init(void)
139{
140	return crypto_register_template(&echainiv_tmpl);
141}
142
143static void __exit echainiv_module_exit(void)
144{
145	crypto_unregister_template(&echainiv_tmpl);
146}
147
148module_init(echainiv_module_init);
149module_exit(echainiv_module_exit);
150
151MODULE_LICENSE("GPL");
152MODULE_DESCRIPTION("Encrypted Chain IV Generator");
153MODULE_ALIAS_CRYPTO("echainiv");