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
  15 struct ecdh_ctx {
  16         unsigned int curve_id;
  17         unsigned int ndigits;
  18         u64 private_key[ECC_MAX_DIGITS];
  19 };
  20
  21 static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
  22 {
  23         return kpp_tfm_ctx(tfm);
  24 }
  25
  26 static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
  27                            unsigned int len)
  28 {
  29         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  30         struct ecdh params;
  31
  32         if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
  33             params.key_size > sizeof(u64) * ctx->ndigits)
  34                 return -EINVAL;
  35
  36         if (!params.key || !params.key_size)
  37                 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  38                                        ctx->private_key);
  39
  40         memcpy(ctx->private_key, params.key, params.key_size);
  41
  42         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  43                              ctx->private_key, params.key_size) < 0) {
  44                 memzero_explicit(ctx->private_key, params.key_size);
  45                 return -EINVAL;
  46         }
  47         return 0;
  48 }
  49
  50 static int ecdh_compute_value(struct kpp_request *req)
  51 {
  52         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  53         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  54         u64 *public_key;
  55         u64 *shared_secret = NULL;
  56         void *buf;
  57         size_t copied, nbytes, public_key_sz;
  58         int ret = -ENOMEM;
  59
  60         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  61         /* Public part is a point thus it has both coordinates */
  62         public_key_sz = 2 * nbytes;
  63
  64         public_key = kmalloc(public_key_sz, GFP_KERNEL);
  65         if (!public_key)
  66                 return -ENOMEM;
  67
  68         if (req->src) {
  69                 shared_secret = kmalloc(nbytes, GFP_KERNEL);
  70                 if (!shared_secret)
  71                         goto free_pubkey;
  72
  73                 /* from here on it's invalid parameters */
  74                 ret = -EINVAL;
  75
  76                 /* must have exactly two points to be on the curve */
  77                 if (public_key_sz != req->src_len)
  78                         goto free_all;
  79
  80                 copied = sg_copy_to_buffer(req->src,
  81                                            sg_nents_for_len(req->src,
  82                                                             public_key_sz),
  83                                            public_key, public_key_sz);
  84                 if (copied != public_key_sz)
  85                         goto free_all;
  86
  87                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
  88                                                 ctx->private_key, public_key,
  89                                                 shared_secret);
  90
  91                 buf = shared_secret;
  92         } else {
  93                 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
  94                                        ctx->private_key, public_key);
  95                 buf = public_key;
  96                 nbytes = public_key_sz;
  97         }
  98
  99         if (ret < 0)
 100                 goto free_all;
 101
 102         /* might want less than we've got */
 103         nbytes = min_t(size_t, nbytes, req->dst_len);
 104         copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
 105                                                                 nbytes),
 106                                      buf, nbytes);
 107         if (copied != nbytes)
 108                 ret = -EINVAL;
 109
 110         /* fall through */
 111 free_all:
 112         kfree_sensitive(shared_secret);
 113 free_pubkey:
 114         kfree(public_key);
 115         return ret;
 116 }
 117
 118 static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 119 {
 120         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 121
 122         /* Public key is made of two coordinates, add one to the left shift */
 123         return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 124 }
 125
 126 static int ecdh_nist_p192_init_tfm(struct crypto_kpp *tfm)
 127 {
 128         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 129
 130         ctx->curve_id = ECC_CURVE_NIST_P192;
 131         ctx->ndigits = ECC_CURVE_NIST_P192_DIGITS;
 132
 133         return 0;
 134 }
 135
 136 static struct kpp_alg ecdh_nist_p192 = {
 137         .set_secret = ecdh_set_secret,
 138         .generate_public_key = ecdh_compute_value,
 139         .compute_shared_secret = ecdh_compute_value,
 140         .max_size = ecdh_max_size,
 141         .init = ecdh_nist_p192_init_tfm,
 142         .base = {
 143                 .cra_name = "ecdh-nist-p192",
 144                 .cra_driver_name = "ecdh-generic",
 145                 .cra_priority = 100,
 146                 .cra_module = THIS_MODULE,
 147                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 148         },
 149 };
 150
 151 static int ecdh_nist_p256_init_tfm(struct crypto_kpp *tfm)
 152 {
 153         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 154
 155         ctx->curve_id = ECC_CURVE_NIST_P256;
 156         ctx->ndigits = ECC_CURVE_NIST_P256_DIGITS;
 157
 158         return 0;
 159 }
 160
 161 static struct kpp_alg ecdh_nist_p256 = {
 162         .set_secret = ecdh_set_secret,
 163         .generate_public_key = ecdh_compute_value,
 164         .compute_shared_secret = ecdh_compute_value,
 165         .max_size = ecdh_max_size,
 166         .init = ecdh_nist_p256_init_tfm,
 167         .base = {
 168                 .cra_name = "ecdh-nist-p256",
 169                 .cra_driver_name = "ecdh-generic",
 170                 .cra_priority = 100,
 171                 .cra_module = THIS_MODULE,
 172                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 173         },
 174 };
 175
 176 static bool ecdh_nist_p192_registered;
 177
 178 static int ecdh_init(void)
 179 {
 180         int ret;
 181
 182         ret = crypto_register_kpp(&ecdh_nist_p192);
 183         ecdh_nist_p192_registered = ret == 0;
 184
 185         return crypto_register_kpp(&ecdh_nist_p256);
 186 }
 187
 188 static void ecdh_exit(void)
 189 {
 190         if (ecdh_nist_p192_registered)
 191                 crypto_unregister_kpp(&ecdh_nist_p192);
 192         crypto_unregister_kpp(&ecdh_nist_p256);
 193 }
 194
 195 subsys_initcall(ecdh_init);
 196 module_exit(ecdh_exit);
 197 MODULE_ALIAS_CRYPTO("ecdh");
 198 MODULE_LICENSE("GPL");
 199 MODULE_DESCRIPTION("ECDH generic algorithm");