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, const void *buf,
  42                            unsigned int len)
  43 {
  44         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  45         struct ecdh params;
  46         unsigned int ndigits;
  47
  48         if (crypto_ecdh_decode_key(buf, len, &params) < 0)
  49                 return -EINVAL;
  50
  51         ndigits = ecdh_supported_curve(params.curve_id);
  52         if (!ndigits)
  53                 return -EINVAL;
  54
  55         ctx->curve_id = params.curve_id;
  56         ctx->ndigits = ndigits;
  57
  58         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  59                              (const u8 *)params.key, params.key_size) < 0)
  60                 return -EINVAL;
  61
  62         memcpy(ctx->private_key, params.key, params.key_size);
  63
  64         return 0;
  65 }
  66
  67 static int ecdh_compute_value(struct kpp_request *req)
  68 {
  69         int ret = 0;
  70         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  71         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  72         size_t copied, nbytes;
  73         void *buf;
  74
  75         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  76
  77         if (req->src) {
  78                 copied = sg_copy_to_buffer(req->src, 1, ctx->public_key,
  79                                            2 * nbytes);
  80                 if (copied != 2 * nbytes)
  81                         return -EINVAL;
  82
  83                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
  84                                          (const u8 *)ctx->private_key, nbytes,
  85                                          (const u8 *)ctx->public_key, 2 * nbytes,
  86                                          (u8 *)ctx->shared_secret, nbytes);
  87
  88                 buf = ctx->shared_secret;
  89         } else {
  90                 ret = ecdh_make_pub_key(ctx->curve_id, ctx->ndigits,
  91                                         (const u8 *)ctx->private_key, nbytes,
  92                                         (u8 *)ctx->public_key,
  93                                         sizeof(ctx->public_key));
  94                 buf = ctx->public_key;
  95                 /* Public part is a point thus it has both coordinates */
  96                 nbytes *= 2;
  97         }
  98
  99         if (ret < 0)
 100                 return ret;
 101
 102         copied = sg_copy_from_buffer(req->dst, 1, buf, nbytes);
 103         if (copied != nbytes)
 104                 return -EINVAL;
 105
 106         return ret;
 107 }
 108
 109 static int ecdh_max_size(struct crypto_kpp *tfm)
 110 {
 111         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 112         int nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
 113
 114         /* Public key is made of two coordinates */
 115         return 2 * nbytes;
 116 }
 117
 118 static void no_exit_tfm(struct crypto_kpp *tfm)
 119 {
 120         return;
 121 }
 122
 123 static struct kpp_alg ecdh = {
 124         .set_secret = ecdh_set_secret,
 125         .generate_public_key = ecdh_compute_value,
 126         .compute_shared_secret = ecdh_compute_value,
 127         .max_size = ecdh_max_size,
 128         .exit = no_exit_tfm,
 129         .base = {
 130                 .cra_name = "ecdh",
 131                 .cra_driver_name = "ecdh-generic",
 132                 .cra_priority = 100,
 133                 .cra_module = THIS_MODULE,
 134                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 135         },
 136 };
 137
 138 static int ecdh_init(void)
 139 {
 140         return crypto_register_kpp(&ecdh);
 141 }
 142
 143 static void ecdh_exit(void)
 144 {
 145         crypto_unregister_kpp(&ecdh);
 146 }
 147
 148 module_init(ecdh_init);
 149 module_exit(ecdh_exit);
 150 MODULE_ALIAS_CRYPTO("ecdh");
 151 MODULE_LICENSE("GPL");
 152 MODULE_DESCRIPTION("ECDH generic algorithm");