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 };
  24
  25 static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
  26 {
  27         return kpp_tfm_ctx(tfm);
  28 }
  29
  30 static unsigned int ecdh_supported_curve(unsigned int curve_id)
  31 {
  32         switch (curve_id) {
  33         case ECC_CURVE_NIST_P192: return 3;
  34         case ECC_CURVE_NIST_P256: return 4;
  35         default: return 0;
  36         }
  37 }
  38
  39 static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
  40                            unsigned int len)
  41 {
  42         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  43         struct ecdh params;
  44         unsigned int ndigits;
  45
  46         if (crypto_ecdh_decode_key(buf, len, &params) < 0)
  47                 return -EINVAL;
  48
  49         ndigits = ecdh_supported_curve(params.curve_id);
  50         if (!ndigits)
  51                 return -EINVAL;
  52
  53         ctx->curve_id = params.curve_id;
  54         ctx->ndigits = ndigits;
  55
  56         if (!params.key || !params.key_size)
  57                 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
  58                                        ctx->private_key);
  59
  60         if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
  61                              (const u64 *)params.key, params.key_size) < 0)
  62                 return -EINVAL;
  63
  64         memcpy(ctx->private_key, params.key, params.key_size);
  65
  66         return 0;
  67 }
  68
  69 static int ecdh_compute_value(struct kpp_request *req)
  70 {
  71         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  72         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
  73         u64 *public_key;
  74         u64 *shared_secret = NULL;
  75         void *buf;
  76         size_t copied, nbytes, public_key_sz;
  77         int ret = -ENOMEM;
  78
  79         nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
  80         /* Public part is a point thus it has both coordinates */
  81         public_key_sz = 2 * nbytes;
  82
  83         public_key = kmalloc(public_key_sz, GFP_KERNEL);
  84         if (!public_key)
  85                 return -ENOMEM;
  86
  87         if (req->src) {
  88                 shared_secret = kmalloc(nbytes, GFP_KERNEL);
  89                 if (!shared_secret)
  90                         goto free_pubkey;
  91
  92                 /* from here on it's invalid parameters */
  93                 ret = -EINVAL;
  94
  95                 /* must have exactly two points to be on the curve */
  96                 if (public_key_sz != req->src_len)
  97                         goto free_all;
  98
  99                 copied = sg_copy_to_buffer(req->src,
 100                                            sg_nents_for_len(req->src,
 101                                                             public_key_sz),
 102                                            public_key, public_key_sz);
 103                 if (copied != public_key_sz)
 104                         goto free_all;
 105
 106                 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
 107                                                 ctx->private_key, public_key,
 108                                                 shared_secret);
 109
 110                 buf = shared_secret;
 111         } else {
 112                 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
 113                                        ctx->private_key, public_key);
 114                 buf = public_key;
 115                 nbytes = public_key_sz;
 116         }
 117
 118         if (ret < 0)
 119                 goto free_all;
 120
 121         /* might want less than we've got */
 122         nbytes = min_t(size_t, nbytes, req->dst_len);
 123         copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
 124                                                                 nbytes),
 125                                      buf, nbytes);
 126         if (copied != nbytes)
 127                 ret = -EINVAL;
 128
 129         /* fall through */
 130 free_all:
 131         kzfree(shared_secret);
 132 free_pubkey:
 133         kfree(public_key);
 134         return ret;
 135 }
 136
 137 static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
 138 {
 139         struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
 140
 141         /* Public key is made of two coordinates, add one to the left shift */
 142         return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
 143 }
 144
 145 static struct kpp_alg ecdh = {
 146         .set_secret = ecdh_set_secret,
 147         .generate_public_key = ecdh_compute_value,
 148         .compute_shared_secret = ecdh_compute_value,
 149         .max_size = ecdh_max_size,
 150         .base = {
 151                 .cra_name = "ecdh",
 152                 .cra_driver_name = "ecdh-generic",
 153                 .cra_priority = 100,
 154                 .cra_module = THIS_MODULE,
 155                 .cra_ctxsize = sizeof(struct ecdh_ctx),
 156         },
 157 };
 158
 159 static int ecdh_init(void)
 160 {
 161         return crypto_register_kpp(&ecdh);
 162 }
 163
 164 static void ecdh_exit(void)
 165 {
 166         crypto_unregister_kpp(&ecdh);
 167 }
 168
 169 module_init(ecdh_init);
 170 module_exit(ecdh_exit);
 171 MODULE_ALIAS_CRYPTO("ecdh");
 172 MODULE_LICENSE("GPL");
 173 MODULE_DESCRIPTION("ECDH generic algorithm");