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;
  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 (dh_check_params_length(params->p_size << 3))
  57                 return -EINVAL;
  58
  59         ctx->p = mpi_read_raw_data(params->p, params->p_size);
  60         if (!ctx->p)
  61                 return -EINVAL;
  62
  63         ctx->g = mpi_read_raw_data(params->g, params->g_size);
  64         if (!ctx->g)
  65                 return -EINVAL;
  66
  67         return 0;
  68 }
  69
  70 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
  71                          unsigned int len)
  72 {
  73         struct dh_ctx *ctx = dh_get_ctx(tfm);
  74         struct dh params;
  75
  76         /* Free the old MPI key if any */
  77         dh_clear_ctx(ctx);
  78
  79         if (crypto_dh_decode_key(buf, len, &params) < 0)
  80                 goto err_clear_ctx;
  81
  82         if (dh_set_params(ctx, &params) < 0)
  83                 goto err_clear_ctx;
  84
  85         ctx->xa = mpi_read_raw_data(params.key, params.key_size);
  86         if (!ctx->xa)
  87                 goto err_clear_ctx;
  88
  89         return 0;
  90
  91 err_clear_ctx:
  92         dh_clear_ctx(ctx);
  93         return -EINVAL;
  94 }
  95
  96 static int dh_compute_value(struct kpp_request *req)
  97 {
  98         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
  99         struct dh_ctx *ctx = dh_get_ctx(tfm);
 100         MPI base, val = mpi_alloc(0);
 101         int ret = 0;
 102         int sign;
 103
 104         if (!val)
 105                 return -ENOMEM;
 106
 107         if (unlikely(!ctx->xa)) {
 108                 ret = -EINVAL;
 109                 goto err_free_val;
 110         }
 111
 112         if (req->src) {
 113                 base = mpi_read_raw_from_sgl(req->src, req->src_len);
 114                 if (!base) {
 115                         ret = -EINVAL;
 116                         goto err_free_val;
 117                 }
 118         } else {
 119                 base = ctx->g;
 120         }
 121
 122         ret = _compute_val(ctx, base, val);
 123         if (ret)
 124                 goto err_free_base;
 125
 126         ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
 127         if (ret)
 128                 goto err_free_base;
 129
 130         if (sign < 0)
 131                 ret = -EBADMSG;
 132 err_free_base:
 133         if (req->src)
 134                 mpi_free(base);
 135 err_free_val:
 136         mpi_free(val);
 137         return ret;
 138 }
 139
 140 static unsigned int dh_max_size(struct crypto_kpp *tfm)
 141 {
 142         struct dh_ctx *ctx = dh_get_ctx(tfm);
 143
 144         return mpi_get_size(ctx->p);
 145 }
 146
 147 static void dh_exit_tfm(struct crypto_kpp *tfm)
 148 {
 149         struct dh_ctx *ctx = dh_get_ctx(tfm);
 150
 151         dh_clear_ctx(ctx);
 152 }
 153
 154 static struct kpp_alg dh = {
 155         .set_secret = dh_set_secret,
 156         .generate_public_key = dh_compute_value,
 157         .compute_shared_secret = dh_compute_value,
 158         .max_size = dh_max_size,
 159         .exit = dh_exit_tfm,
 160         .base = {
 161                 .cra_name = "dh",
 162                 .cra_driver_name = "dh-generic",
 163                 .cra_priority = 100,
 164                 .cra_module = THIS_MODULE,
 165                 .cra_ctxsize = sizeof(struct dh_ctx),
 166         },
 167 };
 168
 169 static int dh_init(void)
 170 {
 171         return crypto_register_kpp(&dh);
 172 }
 173
 174 static void dh_exit(void)
 175 {
 176         crypto_unregister_kpp(&dh);
 177 }
 178
 179 module_init(dh_init);
 180 module_exit(dh_exit);
 181 MODULE_ALIAS_CRYPTO("dh");
 182 MODULE_LICENSE("GPL");
 183 MODULE_DESCRIPTION("DH generic algorithm");