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 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/dh.h>
  16 #include <linux/mpi.h>
  17
  18 struct dh_ctx {
  19         MPI p;
  20         MPI g;
  21         MPI xa;
  22 };
  23
  24 static void dh_clear_ctx(struct dh_ctx *ctx)
  25 {
  26         mpi_free(ctx->p);
  27         mpi_free(ctx->g);
  28         mpi_free(ctx->xa);
  29         memset(ctx, 0, sizeof(*ctx));
  30 }
  31
  32 /*
  33  * If base is g we compute the public key
  34  *      ya = g^xa mod p; [RFC2631 sec 2.1.1]
  35  * else if base if the counterpart public key we compute the shared secret
  36  *      ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
  37  */
  38 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
  39 {
  40         /* val = base^xa mod p */
  41         return mpi_powm(val, base, ctx->xa, ctx->p);
  42 }
  43
  44 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  45 {
  46         return kpp_tfm_ctx(tfm);
  47 }
  48
  49 static int dh_check_params_length(unsigned int p_len)
  50 {
  51         return (p_len < 1536) ? -EINVAL : 0;
  52 }
  53
  54 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
  55 {
  56         if (unlikely(!params->p || !params->g))
  57                 return -EINVAL;
  58
  59         if (dh_check_params_length(params->p_size << 3))
  60                 return -EINVAL;
  61
  62         ctx->p = mpi_read_raw_data(params->p, params->p_size);
  63         if (!ctx->p)
  64                 return -EINVAL;
  65
  66         ctx->g = mpi_read_raw_data(params->g, params->g_size);
  67         if (!ctx->g)
  68                 return -EINVAL;
  69
  70         return 0;
  71 }
  72
  73 static int dh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
  74 {
  75         struct dh_ctx *ctx = dh_get_ctx(tfm);
  76         struct dh params;
  77
  78         /* Free the old MPI key if any */
  79         dh_clear_ctx(ctx);
  80
  81         if (crypto_dh_decode_key(buf, len, &params) < 0)
  82                 goto err_clear_ctx;
  83
  84         if (dh_set_params(ctx, &params) < 0)
  85                 goto err_clear_ctx;
  86
  87         ctx->xa = mpi_read_raw_data(params.key, params.key_size);
  88         if (!ctx->xa)
  89                 goto err_clear_ctx;
  90
  91         return 0;
  92
  93 err_clear_ctx:
  94         dh_clear_ctx(ctx);
  95         return -EINVAL;
  96 }
  97
  98 static int dh_compute_value(struct kpp_request *req)
  99 {
 100         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 101         struct dh_ctx *ctx = dh_get_ctx(tfm);
 102         MPI base, val = mpi_alloc(0);
 103         int ret = 0;
 104         int sign;
 105
 106         if (!val)
 107                 return -ENOMEM;
 108
 109         if (unlikely(!ctx->xa)) {
 110                 ret = -EINVAL;
 111                 goto err_free_val;
 112         }
 113
 114         if (req->src) {
 115                 base = mpi_read_raw_from_sgl(req->src, req->src_len);
 116                 if (!base) {
 117                         ret = EINVAL;
 118                         goto err_free_val;
 119                 }
 120         } else {
 121                 base = ctx->g;
 122         }
 123
 124         ret = _compute_val(ctx, base, val);
 125         if (ret)
 126                 goto err_free_base;
 127
 128         ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
 129         if (ret)
 130                 goto err_free_base;
 131
 132         if (sign < 0)
 133                 ret = -EBADMSG;
 134 err_free_base:
 135         if (req->src)
 136                 mpi_free(base);
 137 err_free_val:
 138         mpi_free(val);
 139         return ret;
 140 }
 141
 142 static int dh_max_size(struct crypto_kpp *tfm)
 143 {
 144         struct dh_ctx *ctx = dh_get_ctx(tfm);
 145
 146         return mpi_get_size(ctx->p);
 147 }
 148
 149 static void dh_exit_tfm(struct crypto_kpp *tfm)
 150 {
 151         struct dh_ctx *ctx = dh_get_ctx(tfm);
 152
 153         dh_clear_ctx(ctx);
 154 }
 155
 156 static struct kpp_alg dh = {
 157         .set_secret = dh_set_secret,
 158         .generate_public_key = dh_compute_value,
 159         .compute_shared_secret = dh_compute_value,
 160         .max_size = dh_max_size,
 161         .exit = dh_exit_tfm,
 162         .base = {
 163                 .cra_name = "dh",
 164                 .cra_driver_name = "dh-generic",
 165                 .cra_priority = 100,
 166                 .cra_module = THIS_MODULE,
 167                 .cra_ctxsize = sizeof(struct dh_ctx),
 168         },
 169 };
 170
 171 static int dh_init(void)
 172 {
 173         return crypto_register_kpp(&dh);
 174 }
 175
 176 static void dh_exit(void)
 177 {
 178         crypto_unregister_kpp(&dh);
 179 }
 180
 181 module_init(dh_init);
 182 module_exit(dh_exit);
 183 MODULE_ALIAS_CRYPTO("dh");
 184 MODULE_LICENSE("GPL");
 185 MODULE_DESCRIPTION("DH generic algorithm");