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added ECDH with OpenSSL (see RFC 4753)

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This commit is contained in:
Tobias Brunner
2008-05-22 11:39:17 +00:00
parent 31430acc1b
commit fc1a31d54b
7 changed files with 446 additions and 5 deletions
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src/libstrongswan/plugins/openssl/openssl_ec_diffie_hellman.c
+360
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/*
* Copyright (C) 2008 Tobias Brunner
* Hochschule fuer Technik Rapperswil
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* $Id$
*/
#include <openssl/ec.h>
#include <openssl/objects.h>
#include "openssl_ec_diffie_hellman.h"
#include <debug.h>
#define COORD_LEN(group) ((EC_GROUP_get_degree(group) + 7) / 8)
typedef struct private_openssl_ec_diffie_hellman_t private_openssl_ec_diffie_hellman_t;
/**
* Private data of an openssl_ec_diffie_hellman_t object.
*/
struct private_openssl_ec_diffie_hellman_t {
/**
* Public openssl_ec_diffie_hellman_t interface.
*/
openssl_ec_diffie_hellman_t public;
/**
* Diffie Hellman group number.
*/
u_int16_t group;
/**
* EC private (public) key
*/
EC_KEY *key;
/**
* EC group
*/
const EC_GROUP *ec_group;
/**
* Other public key
*/
EC_POINT *pub_key;
/**
* Shared secret
*/
chunk_t shared_secret;
/**
* True if shared secret is computed
*/
bool computed;
};
/**
* Convert a chunk to an EC_POINT (which must already exist). The x and y
* coordinates of the point have to be concatenated in the chunk.
*/
static bool chunk2ecp(const EC_GROUP *group, chunk_t chunk, EC_POINT *point)
{
BN_CTX *ctx;
BIGNUM *x, *y;
int coord_len;
bool ret = FALSE;
ctx = BN_CTX_new();
if (!ctx)
{
return FALSE;
}
BN_CTX_start(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (!x || !y)
{
goto error;
}
coord_len = COORD_LEN(group);
if (chunk.len != coord_len * 2)
{
goto error;
}
if (!BN_bin2bn(chunk.ptr, coord_len, x) ||
!BN_bin2bn(chunk.ptr + coord_len, coord_len, y))
{
goto error;
}
if (!EC_POINT_set_affine_coordinates_GFp(group, point, x, y, ctx))
{
goto error;
}
ret = TRUE;
error:
BN_CTX_end(ctx);
BN_CTX_free(ctx);
return ret;
}
/**
* Convert an EC_POINT to a chunk by concatenating the x and y coordinates of
* the point. This function allocates memory for the chunk.
*/
static bool ecp2chunk(const EC_GROUP *group, const EC_POINT *point, chunk_t *chunk)
{
BN_CTX *ctx;
BIGNUM *x, *y;
int coord_len, offset;
bool ret = FALSE;
ctx = BN_CTX_new();
if (!ctx)
{
return FALSE;
}
BN_CTX_start(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (!x || !y)
{
goto error;
}
if (!EC_POINT_get_affine_coordinates_GFp(group, point, x, y, ctx))
{
goto error;
}
coord_len = COORD_LEN(group);
chunk->len = coord_len * 2;
chunk->ptr = malloc(chunk->len);
memset(chunk->ptr, 0, chunk->len);
offset = coord_len - BN_num_bytes(x);
if (!BN_bn2bin(x, chunk->ptr + offset))
{
chunk_free(chunk);
goto error;
}
offset = coord_len - BN_num_bytes(y);
if (!BN_bn2bin(y, chunk->ptr + coord_len + offset))
{
chunk_free(chunk);
goto error;
}
ret = TRUE;
error:
BN_CTX_end(ctx);
BN_CTX_free(ctx);
return ret;
}
/**
* Compute the shared secret.
*
* We cannot use the function ECDH_compute_key() because that returns only the
* x coordinate of the shared secret point (which is defined, for instance, in
* 'NIST SP 800-56A').
* However, we need both coordinates as RFC 4753 says: "The Diffie-Hellman
* public value is obtained by concatenating the x and y values. The format
* of the Diffie-Hellman shared secret value is the same as that of the
* Diffie-Hellman public value."
*/
static bool compute_shared_key(private_openssl_ec_diffie_hellman_t *this, chunk_t *shared_secret)
{
const BIGNUM *priv_key;
EC_POINT *secret;
bool ret = FALSE;
priv_key = EC_KEY_get0_private_key(this->key);
if (!priv_key)
{
goto error;
}
secret = EC_POINT_new(this->ec_group);
if (!secret)
{
goto error;
}
if (!EC_POINT_mul(this->ec_group, secret, NULL, this->pub_key, priv_key, NULL))
{
goto error;
}
if (!ecp2chunk(this->ec_group, secret, shared_secret))
{
goto error;
}
ret = TRUE;
error:
if (secret)
{
EC_POINT_clear_free(secret);
}
return ret;
}
/**
* Implementation of openssl_ec_diffie_hellman_t.set_other_public_value.
*/
static void set_other_public_value(private_openssl_ec_diffie_hellman_t *this, chunk_t value)
{
if (!chunk2ecp(this->ec_group, value, this->pub_key))
{
DBG1("ECDH public value is malformed");
return;
}
chunk_free(&this->shared_secret);
if (!compute_shared_key(this, &this->shared_secret)) {
DBG1("ECDH shared secret computation failed");
return;
}
this->computed = TRUE;
}
/**
* Implementation of openssl_ec_diffie_hellman_t.get_other_public_value.
*/
static status_t get_other_public_value(private_openssl_ec_diffie_hellman_t *this,
chunk_t *value)
{
if (!this->computed)
{
return FAILED;
}
if (!ecp2chunk(this->ec_group, this->pub_key, value))
{
return FAILED;
}
return SUCCESS;
}
/**
* Implementation of openssl_ec_diffie_hellman_t.get_my_public_value.
*/
static void get_my_public_value(private_openssl_ec_diffie_hellman_t *this,chunk_t *value)
{
ecp2chunk(this->ec_group, EC_KEY_get0_public_key(this->key), value);
}
/**
* Implementation of openssl_ec_diffie_hellman_t.get_shared_secret.
*/
static status_t get_shared_secret(private_openssl_ec_diffie_hellman_t *this, chunk_t *secret)
{
if (!this->computed)
{
return FAILED;
}
*secret = chunk_clone(this->shared_secret);
return SUCCESS;
}
/**
* Implementation of openssl_ec_diffie_hellman_t.get_dh_group.
*/
static diffie_hellman_group_t get_dh_group(private_openssl_ec_diffie_hellman_t *this)
{
return this->group;
}
/**
* Implementation of openssl_ec_diffie_hellman_t.destroy.
*/
static void destroy(private_openssl_ec_diffie_hellman_t *this)
{
EC_POINT_clear_free(this->pub_key);
EC_KEY_free(this->key);
chunk_free(&this->shared_secret);
free(this);
}
/*
* Described in header.
*/
openssl_ec_diffie_hellman_t *openssl_ec_diffie_hellman_create(diffie_hellman_group_t group)
{
private_openssl_ec_diffie_hellman_t *this = malloc_thing(private_openssl_ec_diffie_hellman_t);
this->public.dh.get_shared_secret = (status_t (*)(diffie_hellman_t *, chunk_t *)) get_shared_secret;
this->public.dh.set_other_public_value = (void (*)(diffie_hellman_t *, chunk_t )) set_other_public_value;
this->public.dh.get_other_public_value = (status_t (*)(diffie_hellman_t *, chunk_t *)) get_other_public_value;
this->public.dh.get_my_public_value = (void (*)(diffie_hellman_t *, chunk_t *)) get_my_public_value;
this->public.dh.get_dh_group = (diffie_hellman_group_t (*)(diffie_hellman_t *)) get_dh_group;
this->public.dh.destroy = (void (*)(diffie_hellman_t *)) destroy;
switch (group)
{
case ECP_256_BIT:
this->key = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
break;
case ECP_384_BIT:
this->key = EC_KEY_new_by_curve_name(NID_secp384r1);
break;
case ECP_521_BIT:
this->key = EC_KEY_new_by_curve_name(NID_secp521r1);
break;
default:
this->key = NULL;
break;
}
if (!this->key)
{
free(this);
return NULL;
}
/* caching the EC group */
this->ec_group = EC_KEY_get0_group(this->key);
this->pub_key = EC_POINT_new(this->ec_group);
if (!this->pub_key)
{
free(this);
return NULL;
}
/* generate an EC private (public) key */
if (!EC_KEY_generate_key(this->key))
{
free(this);
return NULL;
}
this->group = group;
this->computed = FALSE;
this->shared_secret = chunk_empty;
return &this->public;
}