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	int err;
36
37	if (req->cryptlen < ivsize)
38		return -EINVAL;
39
40	aead_request_set_tfm(subreq, ctx->child);
41
42	info = req->iv;
43
44	if (req->src != req->dst) {
45		SYNC_SKCIPHER_REQUEST_ON_STACK(nreq, ctx->sknull);
46
47		skcipher_request_set_sync_tfm(nreq, ctx->sknull);
48		skcipher_request_set_callback(nreq, req->base.flags,
49					      NULL, NULL);
50		skcipher_request_set_crypt(nreq, req->src, req->dst,
51					   req->assoclen + req->cryptlen,
52					   NULL);
53
54		err = crypto_skcipher_encrypt(nreq);
55		if (err)
56			return err;
57	}
58
59	aead_request_set_callback(subreq, req->base.flags,
60				  req->base.complete, req->base.data);
61	aead_request_set_crypt(subreq, req->dst, req->dst,
62			       req->cryptlen, info);
63	aead_request_set_ad(subreq, req->assoclen);
64
65	memcpy(&nseqno, info + ivsize - 8, 8);
66	seqno = be64_to_cpu(nseqno);
67	memset(info, 0, ivsize);
68
69	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
70
71	do {
72		u64 a;
73
74		memcpy(&a, ctx->salt + ivsize - 8, 8);
75
76		a |= 1;
77		a *= seqno;
78
79		memcpy(info + ivsize - 8, &a, 8);
80	} while ((ivsize -= 8));
81
82	return crypto_aead_encrypt(subreq);
83}
84
85static int echainiv_decrypt(struct aead_request *req)
86{
87	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
88	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
89	struct aead_request *subreq = aead_request_ctx(req);
90	crypto_completion_t compl;
91	void *data;
92	unsigned int ivsize = crypto_aead_ivsize(geniv);
93
94	if (req->cryptlen < ivsize)
95		return -EINVAL;
96
97	aead_request_set_tfm(subreq, ctx->child);
98
99	compl = req->base.complete;
100	data = req->base.data;
101
102	aead_request_set_callback(subreq, req->base.flags, compl, data);
103	aead_request_set_crypt(subreq, req->src, req->dst,
104			       req->cryptlen - ivsize, req->iv);
105	aead_request_set_ad(subreq, req->assoclen + ivsize);
106
107	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);
108
109	return crypto_aead_decrypt(subreq);
110}
111
112static int echainiv_aead_create(struct crypto_template *tmpl,
113				struct rtattr **tb)
114{
115	struct aead_instance *inst;
116	int err;
117
118	inst = aead_geniv_alloc(tmpl, tb);
119
120	if (IS_ERR(inst))
121		return PTR_ERR(inst);
122
123	err = -EINVAL;
124	if (inst->alg.ivsize & (sizeof(u64) - 1) || !inst->alg.ivsize)
125		goto free_inst;
126
127	inst->alg.encrypt = echainiv_encrypt;
128	inst->alg.decrypt = echainiv_decrypt;
129
130	inst->alg.init = aead_init_geniv;
131	inst->alg.exit = aead_exit_geniv;
132
133	inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);
134	inst->alg.base.cra_ctxsize += inst->alg.ivsize;
135
136	err = aead_register_instance(tmpl, inst);
137	if (err) {
138free_inst:
139		inst->free(inst);
140	}
141	return err;
142}
143
144static struct crypto_template echainiv_tmpl = {
145	.name = "echainiv",
146	.create = echainiv_aead_create,
147	.module = THIS_MODULE,
148};
149
150static int __init echainiv_module_init(void)
151{
152	return crypto_register_template(&echainiv_tmpl);
153}
154
155static void __exit echainiv_module_exit(void)
156{
157	crypto_unregister_template(&echainiv_tmpl);
158}
159
160subsys_initcall(echainiv_module_init);
161module_exit(echainiv_module_exit);
162
163MODULE_LICENSE("GPL");
164MODULE_DESCRIPTION("Encrypted Chain IV Generator");
165MODULE_ALIAS_CRYPTO("echainiv");
166