1 /*
2  * echainiv: Encrypted Chain IV Generator
3  *
4  * This generator generates an IV based on a sequence number by multiplying
5  * it with a salt and then encrypting it with the same key as used to encrypt
6  * the plain text.  This algorithm requires that the block size be equal
7  * to the IV size.  It is mainly useful for CBC.
8  *
9  * This generator can only be used by algorithms where authentication
10  * is performed after encryption (i.e., authenc).
11  *
12  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
13  *
14  * This program is free software; you can redistribute it and/or modify it
15  * under the terms of the GNU General Public License as published by the Free
16  * Software Foundation; either version 2 of the License, or (at your option)
17  * any later version.
18  *
19  */
20 
21 #include <crypto/internal/geniv.h>
22 #include <crypto/scatterwalk.h>
23 #include <crypto/skcipher.h>
24 #include <linux/err.h>
25 #include <linux/init.h>
26 #include <linux/kernel.h>
27 #include <linux/module.h>
28 #include <linux/slab.h>
29 #include <linux/string.h>
30 
echainiv_encrypt(struct aead_request * req)31 static int echainiv_encrypt(struct aead_request *req)
32 {
33 	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
34 	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
35 	struct aead_request *subreq = aead_request_ctx(req);
36 	__be64 nseqno;
37 	u64 seqno;
38 	u8 *info;
39 	unsigned int ivsize = crypto_aead_ivsize(geniv);
40 	int err;
41 
42 	if (req->cryptlen < ivsize)
43 		return -EINVAL;
44 
45 	aead_request_set_tfm(subreq, ctx->child);
46 
47 	info = req->iv;
48 
49 	if (req->src != req->dst) {
50 		SKCIPHER_REQUEST_ON_STACK(nreq, ctx->sknull);
51 
52 		skcipher_request_set_tfm(nreq, ctx->sknull);
53 		skcipher_request_set_callback(nreq, req->base.flags,
54 					      NULL, NULL);
55 		skcipher_request_set_crypt(nreq, req->src, req->dst,
56 					   req->assoclen + req->cryptlen,
57 					   NULL);
58 
59 		err = crypto_skcipher_encrypt(nreq);
60 		if (err)
61 			return err;
62 	}
63 
64 	aead_request_set_callback(subreq, req->base.flags,
65 				  req->base.complete, req->base.data);
66 	aead_request_set_crypt(subreq, req->dst, req->dst,
67 			       req->cryptlen, info);
68 	aead_request_set_ad(subreq, req->assoclen);
69 
70 	memcpy(&nseqno, info + ivsize - 8, 8);
71 	seqno = be64_to_cpu(nseqno);
72 	memset(info, 0, ivsize);
73 
74 	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
75 
76 	do {
77 		u64 a;
78 
79 		memcpy(&a, ctx->salt + ivsize - 8, 8);
80 
81 		a |= 1;
82 		a *= seqno;
83 
84 		memcpy(info + ivsize - 8, &a, 8);
85 	} while ((ivsize -= 8));
86 
87 	return crypto_aead_encrypt(subreq);
88 }
89 
echainiv_decrypt(struct aead_request * req)90 static int echainiv_decrypt(struct aead_request *req)
91 {
92 	struct crypto_aead *geniv = crypto_aead_reqtfm(req);
93 	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
94 	struct aead_request *subreq = aead_request_ctx(req);
95 	crypto_completion_t compl;
96 	void *data;
97 	unsigned int ivsize = crypto_aead_ivsize(geniv);
98 
99 	if (req->cryptlen < ivsize)
100 		return -EINVAL;
101 
102 	aead_request_set_tfm(subreq, ctx->child);
103 
104 	compl = req->base.complete;
105 	data = req->base.data;
106 
107 	aead_request_set_callback(subreq, req->base.flags, compl, data);
108 	aead_request_set_crypt(subreq, req->src, req->dst,
109 			       req->cryptlen - ivsize, req->iv);
110 	aead_request_set_ad(subreq, req->assoclen + ivsize);
111 
112 	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);
113 
114 	return crypto_aead_decrypt(subreq);
115 }
116 
echainiv_aead_create(struct crypto_template * tmpl,struct rtattr ** tb)117 static int echainiv_aead_create(struct crypto_template *tmpl,
118 				struct rtattr **tb)
119 {
120 	struct aead_instance *inst;
121 	int err;
122 
123 	inst = aead_geniv_alloc(tmpl, tb, 0, 0);
124 
125 	if (IS_ERR(inst))
126 		return PTR_ERR(inst);
127 
128 	err = -EINVAL;
129 	if (inst->alg.ivsize & (sizeof(u64) - 1) || !inst->alg.ivsize)
130 		goto free_inst;
131 
132 	inst->alg.encrypt = echainiv_encrypt;
133 	inst->alg.decrypt = echainiv_decrypt;
134 
135 	inst->alg.init = aead_init_geniv;
136 	inst->alg.exit = aead_exit_geniv;
137 
138 	inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);
139 	inst->alg.base.cra_ctxsize += inst->alg.ivsize;
140 
141 	inst->free = aead_geniv_free;
142 
143 	err = aead_register_instance(tmpl, inst);
144 	if (err)
145 		goto free_inst;
146 
147 out:
148 	return err;
149 
150 free_inst:
151 	aead_geniv_free(inst);
152 	goto out;
153 }
154 
echainiv_free(struct crypto_instance * inst)155 static void echainiv_free(struct crypto_instance *inst)
156 {
157 	aead_geniv_free(aead_instance(inst));
158 }
159 
160 static struct crypto_template echainiv_tmpl = {
161 	.name = "echainiv",
162 	.create = echainiv_aead_create,
163 	.free = echainiv_free,
164 	.module = THIS_MODULE,
165 };
166 
echainiv_module_init(void)167 static int __init echainiv_module_init(void)
168 {
169 	return crypto_register_template(&echainiv_tmpl);
170 }
171 
echainiv_module_exit(void)172 static void __exit echainiv_module_exit(void)
173 {
174 	crypto_unregister_template(&echainiv_tmpl);
175 }
176 
177 module_init(echainiv_module_init);
178 module_exit(echainiv_module_exit);
179 
180 MODULE_LICENSE("GPL");
181 MODULE_DESCRIPTION("Encrypted Chain IV Generator");
182 MODULE_ALIAS_CRYPTO("echainiv");
183