linux/crypto/echainiv.c
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   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
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