strongswan-ext/src/libstrongswan/plugins/wolfssl/wolfssl_diffie_hellman.c

/*
 * Copyright (C) 2019 Sean Parkinson, wolfSSL Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "wolfssl_common.h"

#ifndef NO_DH

#include <wolfssl/wolfcrypt/dh.h>

#include "wolfssl_diffie_hellman.h"
#include "wolfssl_util.h"

#include <utils/debug.h>

typedef struct private_wolfssl_diffie_hellman_t private_wolfssl_diffie_hellman_t;

/**
 * Private data of an wolfssl_diffie_hellman_t object.
 */
struct private_wolfssl_diffie_hellman_t {
	/**
	 * Public wolfssl_diffie_hellman_t interface.
	 */
	wolfssl_diffie_hellman_t public;

	/**
	 * Diffie Hellman group number.
	 */
	diffie_hellman_group_t group;

	/**
	 * Diffie Hellman object
	 */
	DhKey dh;

	/**
	 * Random number generator to use with RSA operations.
	 */
	WC_RNG rng;

	/**
	 * Length of public values
	 */
	int len;

	/**
	 * Private key
	 */
	chunk_t priv;

	/**
	 * Public key
	 */
	chunk_t pub;

	/**
	 * Shared secret
	 */
	chunk_t shared_secret;

	/**
	 * True if shared secret is computed
	 */
	bool computed;
};

METHOD(diffie_hellman_t, get_my_public_value, bool,
	private_wolfssl_diffie_hellman_t *this, chunk_t *value)
{
	/* Front pad the value with zeros to length of prime */
	*value = chunk_alloc(this->len);
	memset(value->ptr, 0, value->len - this->pub.len);
	memcpy(value->ptr + value->len - this->pub.len, this->pub.ptr,
		   this->pub.len);
	return TRUE;
}

METHOD(diffie_hellman_t, get_shared_secret, bool,
	private_wolfssl_diffie_hellman_t *this, chunk_t *secret)
{
	if (!this->computed)
	{
		return FALSE;
	}

	/* Front pad with zeros to length of prime */
	*secret = chunk_alloc(this->len);
	memset(secret->ptr, 0, secret->len);
	memcpy(secret->ptr + secret->len - this->shared_secret.len,
		   this->shared_secret.ptr, this->shared_secret.len);
	return TRUE;
}


METHOD(diffie_hellman_t, set_other_public_value, bool,
	private_wolfssl_diffie_hellman_t *this, chunk_t value)
{
	word32 len;

	if (!diffie_hellman_verify_value(this->group, value))
	{
		return FALSE;
	}

	chunk_clear(&this->shared_secret);
	this->shared_secret.ptr = malloc(this->len);
	memset(this->shared_secret.ptr, 0xFF, this->shared_secret.len);
	len = this->shared_secret.len;
	if (wc_DhAgree(&this->dh, this->shared_secret.ptr, &len, this->priv.ptr,
				   this->priv.len, value.ptr, value.len) != 0)
	{
		DBG1(DBG_LIB, "DH shared secret computation failed");
		return FALSE;
	}
	this->shared_secret.len = len;
	this->computed = TRUE;
	return TRUE;
}

METHOD(diffie_hellman_t, set_private_value, bool,
	private_wolfssl_diffie_hellman_t *this, chunk_t value)
{
	bool success = FALSE;
	chunk_t g;
	word32 len;
	int ret;

	chunk_clear(&this->priv);
	this->priv = chunk_clone(value);

	/* Calculate public value - g^priv mod p */
	if (wolfssl_mp2chunk(&this->dh.g, &g))
	{
		len = this->pub.len;
		ret = wc_DhAgree(&this->dh, this->pub.ptr, &len, this->priv.ptr,
						 this->priv.len, g.ptr, g.len);
		if (ret == 0) {
			this->pub.len = len;
			success = TRUE;
		}
	}

	free(g.ptr);
	return success;
}

METHOD(diffie_hellman_t, get_dh_group, diffie_hellman_group_t,
	private_wolfssl_diffie_hellman_t *this)
{
	return this->group;
}

/**
 * Lookup the modulus in modulo table
 */
static status_t set_modulus(private_wolfssl_diffie_hellman_t *this)
{
	diffie_hellman_params_t *params = diffie_hellman_get_params(this->group);
	if (!params)
	{
		return NOT_FOUND;
	}

	this->len = params->prime.len;
	if (wc_DhSetKey(&this->dh, params->prime.ptr, params->prime.len,
					params->generator.ptr, params->generator.len) != 0)
	{
		return FAILED;
	}

	return SUCCESS;
}

METHOD(diffie_hellman_t, destroy, void,
	private_wolfssl_diffie_hellman_t *this)
{
	wc_FreeRng(&this->rng);
	wc_FreeDhKey(&this->dh);
	chunk_clear(&this->pub);
	chunk_clear(&this->priv);
	chunk_clear(&this->shared_secret);
	free(this);
}

/**
 * Maximum private key length when generating key
 */
static int wolfssl_priv_key_size(int len)
{
	if (len <= 128)
	{
		return 21;
	}
	if (len <= 256)
	{
		return 29;
	}
	if (len <= 384)
	{
		return 34;
	}
	if (len <= 512)
	{
		return 39;
	}
	if (len <= 640)
	{
		return 42;
	}
	if (len <= 768)
	{
		return 46;
	}
	if (len <= 896)
	{
		return 49;
	}
	if (len <= 1024)
	{
		return 52;
	}
	return len / 20;
}

/*
 * Described in header.
 */
wolfssl_diffie_hellman_t *wolfssl_diffie_hellman_create(
											diffie_hellman_group_t group, ...)
{
	private_wolfssl_diffie_hellman_t *this;
	word32 privLen, pubLen;

	INIT(this,
		.public = {
			.dh = {
				.get_shared_secret = _get_shared_secret,
				.set_other_public_value = _set_other_public_value,
				.get_my_public_value = _get_my_public_value,
				.set_private_value = _set_private_value,
				.get_dh_group = _get_dh_group,
				.destroy = _destroy,
			},
		},
	);

	if (wc_InitRng(&this->rng) != 0)
	{
		free(this);
		return NULL;
	}
	if (wc_InitDhKey(&this->dh) != 0)
	{
		wc_FreeRng(&this->rng);
		free(this);
		return NULL;
	}

	this->group = group;
	this->computed = FALSE;
	this->priv = chunk_empty;
	this->pub = chunk_empty;
	this->shared_secret = chunk_empty;


	if (group == MODP_CUSTOM)
	{
		chunk_t g, p;

		VA_ARGS_GET(group, g, p);
		this->len = p.len;
		if (wc_DhSetKey(&this->dh, p.ptr, p.len, g.ptr, g.len) != 0)
		{
			destroy(this);
			return NULL;
		}
	}
	else
	{
		/* find a modulus according to group */
		if (set_modulus(this) != SUCCESS)
		{
			destroy(this);
			return NULL;
		}
	}

	this->priv = chunk_alloc(wolfssl_priv_key_size(this->len));
	this->pub = chunk_alloc(this->len);
	privLen = this->priv.len;
	pubLen = this->pub.len;
	/* generate my public and private values */
	if (wc_DhGenerateKeyPair(&this->dh, &this->rng, this->priv.ptr, &privLen,
							 this->pub.ptr, &pubLen) != 0)
	{
		destroy(this);
		return NULL;
	}
	this->pub.len = pubLen;
	this->priv.len = privLen;

	return &this->public;
}

#endif /* NO_DH */