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