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
26 static 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
85 static 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
112 static 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) {
138 free_inst:
139 inst->free(inst);
140 }
141 return err;
142 }
143
144 static struct crypto_template echainiv_tmpl = {
145 .name = "echainiv",
146 .create = echainiv_aead_create,
147 .module = THIS_MODULE,
148 };
149
150 static int __init echainiv_module_init(void)
151 {
152 return crypto_register_template(&echainiv_tmpl);
153 }
154
155 static void __exit echainiv_module_exit(void)
156 {
157 crypto_unregister_template(&echainiv_tmpl);
158 }
159
160 subsys_initcall(echainiv_module_init);
161 module_exit(echainiv_module_exit);
162
163 MODULE_LICENSE("GPL");
164 MODULE_DESCRIPTION("Encrypted Chain IV Generator");
165 MODULE_ALIAS_CRYPTO("echainiv");
166
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