crypto/ecdh.c

   1 /* ECDH key-agreement protocol
   2  *
   3  * Copyright (c) 2016, Intel Corporation
   4  * Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <crypto/internal/kpp.h>
  14 #include <crypto/kpp.h>
  15 #include <crypto/ecdh.h>
  16 #include <linux/scatterlist.h>
  17 #include "ecc.h"
  18
  19 struct ecdh_ctx {
  20         unsigned int curve_id;
  21         unsigned int ndigits;
  22         u64 private_key[ECC_MAX_DIGITS];
  23         u64 public_key[2 * ECC_MAX_DIGITS];
  24         u64 shared_secret[ECC_MAX_DIGITS];
  25 };
  26
  27 static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
  28 {
  29         return kpp_tfm_ctx(tfm);
  30 }
  31
  32 static unsigned int ecdh_supported_curve(unsigned int curve_id)
  33 {
  34         switch (curve_id) {
  35         case ECC_CURVE_NIST_P192: return 3;
  36         case ECC_CURVE_NIST_P256: return 4;
  37         default: return 0;
  38         }
  39 }
  40
  41 static int ecdh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
  42 {
  43         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  44         struct ecdh params;
  45         unsigned int ndigits;
  46
  47         if (crypto_ecdh_decode_key(buf, len, &params) < 0)
  48                 return -EINVAL;
  49
  50         ndigits = ecdh_supported_curve(params.curve_id);
  51         if (!ndigits)
  52                 return -EINVAL;
  53
  54         ctx->curve_id = params.curve_id;
  55         ctx->ndigits = ndigits;
  56
  57         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  58                              (const u8 *)params.key, params.key_size) < 0)
  59                 return -EINVAL;
  60
  61         memcpy(ctx->private_key, params.key, params.key_size);
  62
  63         return 0;
  64 }
  65
  66 static int ecdh_compute_value(struct kpp_request *req)
  67 {
  68         int ret = 0;
  69         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  70         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  71         size_t copied, nbytes;
  72         void *buf;
  73
  74         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  75
  76         if (req->src) {
  77                 copied = sg_copy_to_buffer(req->src, 1, ctx->public_key,
  78                                            2 * nbytes);
  79                 if (copied != 2 * nbytes)
  80                         return -EINVAL;
  81
  82                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
  83                                          (const u8 *)ctx->private_key, nbytes,
  84                                          (const u8 *)ctx->public_key, 2 * nbytes,
  85                                          (u8 *)ctx->shared_secret, nbytes);
  86
  87                 buf = ctx->shared_secret;
  88         } else {
  89                 ret = ecdh_make_pub_key(ctx->curve_id, ctx->ndigits,
  90                                         (const u8 *)ctx->private_key, nbytes,
  91                                         (u8 *)ctx->public_key,
  92                                         sizeof(ctx->public_key));
  93                 buf = ctx->public_key;
  94                 /* Public part is a point thus it has both coordinates */
  95                 nbytes *= 2;
  96         }
  97
  98         if (ret < 0)
  99                 return ret;
 100
 101         copied = sg_copy_from_buffer(req->dst, 1, buf, nbytes);
 102         if (copied != nbytes)
 103                 return -EINVAL;
 104
 105         return ret;
 106 }
 107
 108 static int ecdh_max_size(struct crypto_kpp *tfm)
 109 {
 110         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 111         int nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 112
 113         /* Public key is made of two coordinates */
 114         return 2 * nbytes;
 115 }
 116
 117 static void no_exit_tfm(struct crypto_kpp *tfm)
 118 {
 119         return;
 120 }
 121
 122 static struct kpp_alg ecdh = {
 123         .set_secret = ecdh_set_secret,
 124         .generate_public_key = ecdh_compute_value,
 125         .compute_shared_secret = ecdh_compute_value,
 126         .max_size = ecdh_max_size,
 127         .exit = no_exit_tfm,
 128         .base = {
 129                 .cra_name = "ecdh",
 130                 .cra_driver_name = "ecdh-generic",
 131                 .cra_priority = 100,
 132                 .cra_module = THIS_MODULE,
 133                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 134         },
 135 };
 136
 137 static int ecdh_init(void)
 138 {
 139         return crypto_register_kpp(&ecdh);
 140 }
 141
 142 static void ecdh_exit(void)
 143 {
 144         crypto_unregister_kpp(&ecdh);
 145 }
 146
 147 module_init(ecdh_init);
 148 module_exit(ecdh_exit);
 149 MODULE_ALIAS_CRYPTO("ecdh");
 150 MODULE_LICENSE("GPL");
 151 MODULE_DESCRIPTION("ECDH generic algorithm");