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 License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, 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 (!params.key || !params.key_size)
  59                 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  60                                        ctx->private_key);
  61
  62         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  63                              (const u64 *)params.key, params.key_size) < 0)
  64                 return -EINVAL;
  65
  66         memcpy(ctx->private_key, params.key, params.key_size);
  67
  68         return 0;
  69 }
  70
  71 static int ecdh_compute_value(struct kpp_request *req)
  72 {
  73         int ret = 0;
  74         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  75         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  76         size_t copied, nbytes;
  77         void *buf;
  78
  79         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  80
  81         if (req->src) {
  82                 copied = sg_copy_to_buffer(req->src, 1, ctx->public_key,
  83                                            2 * nbytes);
  84                 if (copied != 2 * nbytes)
  85                         return -EINVAL;
  86
  87                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
  88                                                 ctx->private_key,
  89                                                 ctx->public_key,
  90                                                 ctx->shared_secret);
  91
  92                 buf = ctx->shared_secret;
  93         } else {
  94                 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
  95                                        ctx->private_key, ctx->public_key);
  96                 buf = ctx->public_key;
  97                 /* Public part is a point thus it has both coordinates */
  98                 nbytes *= 2;
  99         }
 100
 101         if (ret < 0)
 102                 return ret;
 103
 104         copied = sg_copy_from_buffer(req->dst, 1, buf, nbytes);
 105         if (copied != nbytes)
 106                 return -EINVAL;
 107
 108         return ret;
 109 }
 110
 111 static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 112 {
 113         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 114
 115         /* Public key is made of two coordinates, add one to the left shift */
 116         return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 117 }
 118
 119 static void no_exit_tfm(struct crypto_kpp *tfm)
 120 {
 121         return;
 122 }
 123
 124 static struct kpp_alg ecdh = {
 125         .set_secret = ecdh_set_secret,
 126         .generate_public_key = ecdh_compute_value,
 127         .compute_shared_secret = ecdh_compute_value,
 128         .max_size = ecdh_max_size,
 129         .exit = no_exit_tfm,
 130         .base = {
 131                 .cra_name = "ecdh",
 132                 .cra_driver_name = "ecdh-generic",
 133                 .cra_priority = 100,
 134                 .cra_module = THIS_MODULE,
 135                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 136         },
 137 };
 138
 139 static int ecdh_init(void)
 140 {
 141         return crypto_register_kpp(&ecdh);
 142 }
 143
 144 static void ecdh_exit(void)
 145 {
 146         crypto_unregister_kpp(&ecdh);
 147 }
 148
 149 module_init(ecdh_init);
 150 module_exit(ecdh_exit);
 151 MODULE_ALIAS_CRYPTO("ecdh");
 152 MODULE_LICENSE("GPL");
 153 MODULE_DESCRIPTION("ECDH generic algorithm");