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Linux/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");
152 

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