LXR linux/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
  18struct dh_ctx {
  19        MPI p;
  20        MPI g;
  21        MPI xa;
  22};
  23
  24static 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 */
  38static 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
  44static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  45{
  46        return kpp_tfm_ctx(tfm);
  47}
  48
  49static int dh_check_params_length(unsigned int p_len)
  50{
  51        return (p_len < 1536) ? -EINVAL : 0;
  52}
  53
  54static 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
  70static 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
  91err_clear_ctx:
  92        dh_clear_ctx(ctx);
  93        return -EINVAL;
  94}
  95
  96static 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;
 132err_free_base:
 133        if (req->src)
 134                mpi_free(base);
 135err_free_val:
 136        mpi_free(val);
 137        return ret;
 138}
 139
 140static 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
 147static 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
 154static 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
 169static int dh_init(void)
 170{
 171        return crypto_register_kpp(&dh);
 172}
 173
 174static void dh_exit(void)
 175{
 176        crypto_unregister_kpp(&dh);
 177}
 178
 179module_init(dh_init);
 180module_exit(dh_exit);
 181MODULE_ALIAS_CRYPTO("dh");
 182MODULE_LICENSE("GPL");
 183MODULE_DESCRIPTION("DH generic algorithm");
 184