LXR linux/crypto/ecdh.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* ECDH key-agreement protocol
   3 *
   4 * Copyright (c) 2016, Intel Corporation
   5 * Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
   6 */
   7
   8#include <linux/module.h>
   9#include <crypto/internal/kpp.h>
  10#include <crypto/kpp.h>
  11#include <crypto/ecdh.h>
  12#include <linux/scatterlist.h>
  13#include "ecc.h"
  14
  15struct ecdh_ctx {
  16        unsigned int curve_id;
  17        unsigned int ndigits;
  18        u64 private_key[ECC_MAX_DIGITS];
  19};
  20
  21static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
  22{
  23        return kpp_tfm_ctx(tfm);
  24}
  25
  26static unsigned int ecdh_supported_curve(unsigned int curve_id)
  27{
  28        switch (curve_id) {
  29        case ECC_CURVE_NIST_P192: return ECC_CURVE_NIST_P192_DIGITS;
  30        case ECC_CURVE_NIST_P256: return ECC_CURVE_NIST_P256_DIGITS;
  31        default: return 0;
  32        }
  33}
  34
  35static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
  36                           unsigned int len)
  37{
  38        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  39        struct ecdh params;
  40        unsigned int ndigits;
  41
  42        if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
  43            params.key_size > sizeof(ctx->private_key))
  44                return -EINVAL;
  45
  46        ndigits = ecdh_supported_curve(params.curve_id);
  47        if (!ndigits)
  48                return -EINVAL;
  49
  50        ctx->curve_id = params.curve_id;
  51        ctx->ndigits = ndigits;
  52
  53        if (!params.key || !params.key_size)
  54                return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  55                                       ctx->private_key);
  56
  57        memcpy(ctx->private_key, params.key, params.key_size);
  58
  59        if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  60                             ctx->private_key, params.key_size) < 0) {
  61                memzero_explicit(ctx->private_key, params.key_size);
  62                return -EINVAL;
  63        }
  64        return 0;
  65}
  66
  67static int ecdh_compute_value(struct kpp_request *req)
  68{
  69        struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  70        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  71        u64 *public_key;
  72        u64 *shared_secret = NULL;
  73        void *buf;
  74        size_t copied, nbytes, public_key_sz;
  75        int ret = -ENOMEM;
  76
  77        nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  78        /* Public part is a point thus it has both coordinates */
  79        public_key_sz = 2 * nbytes;
  80
  81        public_key = kmalloc(public_key_sz, GFP_KERNEL);
  82        if (!public_key)
  83                return -ENOMEM;
  84
  85        if (req->src) {
  86                shared_secret = kmalloc(nbytes, GFP_KERNEL);
  87                if (!shared_secret)
  88                        goto free_pubkey;
  89
  90                /* from here on it's invalid parameters */
  91                ret = -EINVAL;
  92
  93                /* must have exactly two points to be on the curve */
  94                if (public_key_sz != req->src_len)
  95                        goto free_all;
  96
  97                copied = sg_copy_to_buffer(req->src,
  98                                           sg_nents_for_len(req->src,
  99                                                            public_key_sz),
 100                                           public_key, public_key_sz);
 101                if (copied != public_key_sz)
 102                        goto free_all;
 103
 104                ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
 105                                                ctx->private_key, public_key,
 106                                                shared_secret);
 107
 108                buf = shared_secret;
 109        } else {
 110                ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
 111                                       ctx->private_key, public_key);
 112                buf = public_key;
 113                nbytes = public_key_sz;
 114        }
 115
 116        if (ret < 0)
 117                goto free_all;
 118
 119        /* might want less than we've got */
 120        nbytes = min_t(size_t, nbytes, req->dst_len);
 121        copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
 122                                                                nbytes),
 123                                     buf, nbytes);
 124        if (copied != nbytes)
 125                ret = -EINVAL;
 126
 127        /* fall through */
 128free_all:
 129        kfree_sensitive(shared_secret);
 130free_pubkey:
 131        kfree(public_key);
 132        return ret;
 133}
 134
 135static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 136{
 137        struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 138
 139        /* Public key is made of two coordinates, add one to the left shift */
 140        return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 141}
 142
 143static struct kpp_alg ecdh = {
 144        .set_secret = ecdh_set_secret,
 145        .generate_public_key = ecdh_compute_value,
 146        .compute_shared_secret = ecdh_compute_value,
 147        .max_size = ecdh_max_size,
 148        .base = {
 149                .cra_name = "ecdh",
 150                .cra_driver_name = "ecdh-generic",
 151                .cra_priority = 100,
 152                .cra_module = THIS_MODULE,
 153                .cra_ctxsize = sizeof(struct ecdh_ctx),
 154        },
 155};
 156
 157static int ecdh_init(void)
 158{
 159        return crypto_register_kpp(&ecdh);
 160}
 161
 162static void ecdh_exit(void)
 163{
 164        crypto_unregister_kpp(&ecdh);
 165}
 166
 167subsys_initcall(ecdh_init);
 168module_exit(ecdh_exit);
 169MODULE_ALIAS_CRYPTO("ecdh");
 170MODULE_LICENSE("GPL");
 171MODULE_DESCRIPTION("ECDH generic algorithm");
 172