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                 return -EINVAL;
  44
  45         ndigits = ecdh_supported_curve(params.curve_id);
  46         if (!ndigits)
  47                 return -EINVAL;
  48
  49         ctx->curve_id = params.curve_id;
  50         ctx->ndigits = ndigits;
  51
  52         if (!params.key || !params.key_size)
  53                 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  54                                        ctx->private_key);
  55
  56         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  57                              (const u64 *)params.key, params.key_size) < 0)
  58                 return -EINVAL;
  59
  60         memcpy(ctx->private_key, params.key, params.key_size);
  61
  62         return 0;
  63 }
  64
  65 static int ecdh_compute_value(struct kpp_request *req)
  66 {
  67         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  68         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  69         u64 *public_key;
  70         u64 *shared_secret = NULL;
  71         void *buf;
  72         size_t copied, nbytes, public_key_sz;
  73         int ret = -ENOMEM;
  74
  75         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  76         /* Public part is a point thus it has both coordinates */
  77         public_key_sz = 2 * nbytes;
  78
  79         public_key = kmalloc(public_key_sz, GFP_KERNEL);
  80         if (!public_key)
  81                 return -ENOMEM;
  82
  83         if (req->src) {
  84                 shared_secret = kmalloc(nbytes, GFP_KERNEL);
  85                 if (!shared_secret)
  86                         goto free_pubkey;
  87
  88                 /* from here on it's invalid parameters */
  89                 ret = -EINVAL;
  90
  91                 /* must have exactly two points to be on the curve */
  92                 if (public_key_sz != req->src_len)
  93                         goto free_all;
  94
  95                 copied = sg_copy_to_buffer(req->src,
  96                                            sg_nents_for_len(req->src,
  97                                                             public_key_sz),
  98                                            public_key, public_key_sz);
  99                 if (copied != public_key_sz)
 100                         goto free_all;
 101
 102                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
 103                                                 ctx->private_key, public_key,
 104                                                 shared_secret);
 105
 106                 buf = shared_secret;
 107         } else {
 108                 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
 109                                        ctx->private_key, public_key);
 110                 buf = public_key;
 111                 nbytes = public_key_sz;
 112         }
 113
 114         if (ret < 0)
 115                 goto free_all;
 116
 117         /* might want less than we've got */
 118         nbytes = min_t(size_t, nbytes, req->dst_len);
 119         copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
 120                                                                 nbytes),
 121                                      buf, nbytes);
 122         if (copied != nbytes)
 123                 ret = -EINVAL;
 124
 125         /* fall through */
 126 free_all:
 127         kzfree(shared_secret);
 128 free_pubkey:
 129         kfree(public_key);
 130         return ret;
 131 }
 132
 133 static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 134 {
 135         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 136
 137         /* Public key is made of two coordinates, add one to the left shift */
 138         return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 139 }
 140
 141 static struct kpp_alg ecdh = {
 142         .set_secret = ecdh_set_secret,
 143         .generate_public_key = ecdh_compute_value,
 144         .compute_shared_secret = ecdh_compute_value,
 145         .max_size = ecdh_max_size,
 146         .base = {
 147                 .cra_name = "ecdh",
 148                 .cra_driver_name = "ecdh-generic",
 149                 .cra_priority = 100,
 150                 .cra_module = THIS_MODULE,
 151                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 152         },
 153 };
 154
 155 static int ecdh_init(void)
 156 {
 157         return crypto_register_kpp(&ecdh);
 158 }
 159
 160 static void ecdh_exit(void)
 161 {
 162         crypto_unregister_kpp(&ecdh);
 163 }
 164
 165 subsys_initcall(ecdh_init);
 166 module_exit(ecdh_exit);
 167 MODULE_ALIAS_CRYPTO("ecdh");
 168 MODULE_LICENSE("GPL");
 169 MODULE_DESCRIPTION("ECDH generic algorithm");