crypto/dh.c

   1 /*  Diffie-Hellman Key Agreement Method [RFC2631]
   2  *
   3  * Copyright (c) 2016, Intel Corporation
   4  * Authors: Salvatore 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/dh.h>
  16 #include <linux/mpi.h>
  17
  18 struct dh_ctx {
  19         MPI p;  /* Value is guaranteed to be set. */
  20         MPI q;  /* Value is optional. */
  21         MPI g;  /* Value is guaranteed to be set. */
  22         MPI xa; /* Value is guaranteed to be set. */
  23 };
  24
  25 static void dh_clear_ctx(struct dh_ctx *ctx)
  26 {
  27         mpi_free(ctx->p);
  28         mpi_free(ctx->q);
  29         mpi_free(ctx->g);
  30         mpi_free(ctx->xa);
  31         memset(ctx, 0, sizeof(*ctx));
  32 }
  33
  34 /*
  35  * If base is g we compute the public key
  36  *      ya = g^xa mod p; [RFC2631 sec 2.1.1]
  37  * else if base if the counterpart public key we compute the shared secret
  38  *      ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
  39  */
  40 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
  41 {
  42         /* val = base^xa mod p */
  43         return mpi_powm(val, base, ctx->xa, ctx->p);
  44 }
  45
  46 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  47 {
  48         return kpp_tfm_ctx(tfm);
  49 }
  50
  51 static int dh_check_params_length(unsigned int p_len)
  52 {
  53         return (p_len < 1536) ? -EINVAL : 0;
  54 }
  55
  56 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
  57 {
  58         if (dh_check_params_length(params->p_size << 3))
  59                 return -EINVAL;
  60
  61         ctx->p = mpi_read_raw_data(params->p, params->p_size);
  62         if (!ctx->p)
  63                 return -EINVAL;
  64
  65         if (params->q && params->q_size) {
  66                 ctx->q = mpi_read_raw_data(params->q, params->q_size);
  67                 if (!ctx->q)
  68                         return -EINVAL;
  69         }
  70
  71         ctx->g = mpi_read_raw_data(params->g, params->g_size);
  72         if (!ctx->g)
  73                 return -EINVAL;
  74
  75         return 0;
  76 }
  77
  78 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
  79                          unsigned int len)
  80 {
  81         struct dh_ctx *ctx = dh_get_ctx(tfm);
  82         struct dh params;
  83
  84         /* Free the old MPI key if any */
  85         dh_clear_ctx(ctx);
  86
  87         if (crypto_dh_decode_key(buf, len, &params) < 0)
  88                 goto err_clear_ctx;
  89
  90         if (dh_set_params(ctx, &params) < 0)
  91                 goto err_clear_ctx;
  92
  93         ctx->xa = mpi_read_raw_data(params.key, params.key_size);
  94         if (!ctx->xa)
  95                 goto err_clear_ctx;
  96
  97         return 0;
  98
  99 err_clear_ctx:
 100         dh_clear_ctx(ctx);
 101         return -EINVAL;
 102 }
 103
 104 /*
 105  * SP800-56A public key verification:
 106  *
 107  * * If Q is provided as part of the domain paramenters, a full validation
 108  *   according to SP800-56A section 5.6.2.3.1 is performed.
 109  *
 110  * * If Q is not provided, a partial validation according to SP800-56A section
 111  *   5.6.2.3.2 is performed.
 112  */
 113 static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
 114 {
 115         if (unlikely(!ctx->p))
 116                 return -EINVAL;
 117
 118         /*
 119          * Step 1: Verify that 2 <= y <= p - 2.
 120          *
 121          * The upper limit check is actually y < p instead of y < p - 1
 122          * as the mpi_sub_ui function is yet missing.
 123          */
 124         if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
 125                 return -EINVAL;
 126
 127         /* Step 2: Verify that 1 = y^q mod p */
 128         if (ctx->q) {
 129                 MPI val = mpi_alloc(0);
 130                 int ret;
 131
 132                 if (!val)
 133                         return -ENOMEM;
 134
 135                 ret = mpi_powm(val, y, ctx->q, ctx->p);
 136
 137                 if (ret) {
 138                         mpi_free(val);
 139                         return ret;
 140                 }
 141
 142                 ret = mpi_cmp_ui(val, 1);
 143
 144                 mpi_free(val);
 145
 146                 if (ret != 0)
 147                         return -EINVAL;
 148         }
 149
 150         return 0;
 151 }
 152
 153 static int dh_compute_value(struct kpp_request *req)
 154 {
 155         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 156         struct dh_ctx *ctx = dh_get_ctx(tfm);
 157         MPI base, val = mpi_alloc(0);
 158         int ret = 0;
 159         int sign;
 160
 161         if (!val)
 162                 return -ENOMEM;
 163
 164         if (unlikely(!ctx->xa)) {
 165                 ret = -EINVAL;
 166                 goto err_free_val;
 167         }
 168
 169         if (req->src) {
 170                 base = mpi_read_raw_from_sgl(req->src, req->src_len);
 171                 if (!base) {
 172                         ret = -EINVAL;
 173                         goto err_free_val;
 174                 }
 175                 ret = dh_is_pubkey_valid(ctx, base);
 176                 if (ret)
 177                         goto err_free_base;
 178         } else {
 179                 base = ctx->g;
 180         }
 181
 182         ret = _compute_val(ctx, base, val);
 183         if (ret)
 184                 goto err_free_base;
 185
 186         ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
 187         if (ret)
 188                 goto err_free_base;
 189
 190         if (sign < 0)
 191                 ret = -EBADMSG;
 192 err_free_base:
 193         if (req->src)
 194                 mpi_free(base);
 195 err_free_val:
 196         mpi_free(val);
 197         return ret;
 198 }
 199
 200 static unsigned int dh_max_size(struct crypto_kpp *tfm)
 201 {
 202         struct dh_ctx *ctx = dh_get_ctx(tfm);
 203
 204         return mpi_get_size(ctx->p);
 205 }
 206
 207 static void dh_exit_tfm(struct crypto_kpp *tfm)
 208 {
 209         struct dh_ctx *ctx = dh_get_ctx(tfm);
 210
 211         dh_clear_ctx(ctx);
 212 }
 213
 214 static struct kpp_alg dh = {
 215         .set_secret = dh_set_secret,
 216         .generate_public_key = dh_compute_value,
 217         .compute_shared_secret = dh_compute_value,
 218         .max_size = dh_max_size,
 219         .exit = dh_exit_tfm,
 220         .base = {
 221                 .cra_name = "dh",
 222                 .cra_driver_name = "dh-generic",
 223                 .cra_priority = 100,
 224                 .cra_module = THIS_MODULE,
 225                 .cra_ctxsize = sizeof(struct dh_ctx),
 226         },
 227 };
 228
 229 static int dh_init(void)
 230 {
 231         return crypto_register_kpp(&dh);
 232 }
 233
 234 static void dh_exit(void)
 235 {
 236         crypto_unregister_kpp(&dh);
 237 }
 238
 239 module_init(dh_init);
 240 module_exit(dh_exit);
 241 MODULE_ALIAS_CRYPTO("dh");
 242 MODULE_LICENSE("GPL");
 243 MODULE_DESCRIPTION("DH generic algorithm");