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 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
  35 static 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
  67 static 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 */
 128 free_all:
 129         kfree_sensitive(shared_secret);
 130 free_pubkey:
 131         kfree(public_key);
 132         return ret;
 133 }
 134
 135 static 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
 143 static 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
 157 static int ecdh_init(void)
 158 {
 159         return crypto_register_kpp(&ecdh);
 160 }
 161
 162 static void ecdh_exit(void)
 163 {
 164         crypto_unregister_kpp(&ecdh);
 165 }
 166
 167 subsys_initcall(ecdh_init);
 168 module_exit(ecdh_exit);
 169 MODULE_ALIAS_CRYPTO("ecdh");
 170 MODULE_LICENSE("GPL");
 171 MODULE_DESCRIPTION("ECDH generic algorithm");