LXR linux/crypto/ecdh.c

   1/* ECDH key-agreement protocol
   2 *
   3 * Copyright (c) 2016, Intel Corporation
   4 * Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#include <linux/module.h>
  13#include <crypto/internal/kpp.h>
  14#include <crypto/kpp.h>
  15#include <crypto/ecdh.h>
  16#include <linux/scatterlist.h>
  17#include "ecc.h"
  18
  19struct ecdh_ctx {
  20        unsigned int curve_id;
  21        unsigned int ndigits;
  22        u64 private_key[ECC_MAX_DIGITS];
  23};
  24
  25static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
  26{
  27        return kpp_tfm_ctx(tfm);
  28}
  29
  30static unsigned int ecdh_supported_curve(unsigned int curve_id)
  31{
  32        switch (curve_id) {
  33        case ECC_CURVE_NIST_P192: return 3;
  34        case ECC_CURVE_NIST_P256: return 4;
  35        default: return 0;
  36        }
  37}
  38
  39static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
  40                           unsigned int len)
  41{
  42        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  43        struct ecdh params;
  44        unsigned int ndigits;
  45
  46        if (crypto_ecdh_decode_key(buf, len, &params) < 0)
  47                return -EINVAL;
  48
  49        ndigits = ecdh_supported_curve(params.curve_id);
  50        if (!ndigits)
  51                return -EINVAL;
  52
  53        ctx->curve_id = params.curve_id;
  54        ctx->ndigits = ndigits;
  55
  56        if (!params.key || !params.key_size)
  57                return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  58                                       ctx->private_key);
  59
  60        if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  61                             (const u64 *)params.key, params.key_size) < 0)
  62                return -EINVAL;
  63
  64        memcpy(ctx->private_key, params.key, params.key_size);
  65
  66        return 0;
  67}
  68
  69static int ecdh_compute_value(struct kpp_request *req)
  70{
  71        struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  72        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  73        u64 *public_key;
  74        u64 *shared_secret = NULL;
  75        void *buf;
  76        size_t copied, nbytes, public_key_sz;
  77        int ret = -ENOMEM;
  78
  79        nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  80        /* Public part is a point thus it has both coordinates */
  81        public_key_sz = 2 * nbytes;
  82
  83        public_key = kmalloc(public_key_sz, GFP_KERNEL);
  84        if (!public_key)
  85                return -ENOMEM;
  86
  87        if (req->src) {
  88                shared_secret = kmalloc(nbytes, GFP_KERNEL);
  89                if (!shared_secret)
  90                        goto free_pubkey;
  91
  92                /* from here on it's invalid parameters */
  93                ret = -EINVAL;
  94
  95                /* must have exactly two points to be on the curve */
  96                if (public_key_sz != req->src_len)
  97                        goto free_all;
  98
  99                copied = sg_copy_to_buffer(req->src,
 100                                           sg_nents_for_len(req->src,
 101                                                            public_key_sz),
 102                                           public_key, public_key_sz);
 103                if (copied != public_key_sz)
 104                        goto free_all;
 105
 106                ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
 107                                                ctx->private_key, public_key,
 108                                                shared_secret);
 109
 110                buf = shared_secret;
 111        } else {
 112                ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
 113                                       ctx->private_key, public_key);
 114                buf = public_key;
 115                nbytes = public_key_sz;
 116        }
 117
 118        if (ret < 0)
 119                goto free_all;
 120
 121        /* might want less than we've got */
 122        nbytes = min_t(size_t, nbytes, req->dst_len);
 123        copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
 124                                                                nbytes),
 125                                     buf, nbytes);
 126        if (copied != nbytes)
 127                ret = -EINVAL;
 128
 129        /* fall through */
 130free_all:
 131        kzfree(shared_secret);
 132free_pubkey:
 133        kfree(public_key);
 134        return ret;
 135}
 136
 137static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 138{
 139        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 140
 141        /* Public key is made of two coordinates, add one to the left shift */
 142        return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 143}
 144
 145static struct kpp_alg ecdh = {
 146        .set_secret = ecdh_set_secret,
 147        .generate_public_key = ecdh_compute_value,
 148        .compute_shared_secret = ecdh_compute_value,
 149        .max_size = ecdh_max_size,
 150        .base = {
 151                .cra_name = "ecdh",
 152                .cra_driver_name = "ecdh-generic",
 153                .cra_priority = 100,
 154                .cra_module = THIS_MODULE,
 155                .cra_ctxsize = sizeof(struct ecdh_ctx),
 156        },
 157};
 158
 159static int ecdh_init(void)
 160{
 161        return crypto_register_kpp(&ecdh);
 162}
 163
 164static void ecdh_exit(void)
 165{
 166        crypto_unregister_kpp(&ecdh);
 167}
 168
 169module_init(ecdh_init);
 170module_exit(ecdh_exit);
 171MODULE_ALIAS_CRYPTO("ecdh");
 172MODULE_LICENSE("GPL");
 173MODULE_DESCRIPTION("ECDH generic algorithm");
 174