openssl3.2 - 官方demo学习 - keyexch - x25519.c

openssl3.2 - 官方demo学习 - keyexch - x25519.c

概述

官方程序中演示了私钥2种key交换的情况:

1. 产生X25519的key对(私钥/公钥), 并交换公钥给对方, 并分别产生会话密钥, 使双方都能持有相同的会话密钥

2. 产生X25519的key对(私钥/公钥)时, 产生私钥时, 可以随机产生. 这个私钥是为会话准备的, 然后根据会话私钥产生会话公钥.
   然后交换公钥给对方, 并分别产生会话密钥, 使双方都能持有相同的会话密钥

可以看到case2更安全, 密钥不在程序中定义.

笔记

/*!
\file x25519.c
\note openssl3.2 - 官方demo学习 - keyexch - x25519.c

官方程序中演示了私钥2种key交换的情况:

1. 产生X25519的key对(私钥/公钥), 并交换公钥给对方, 并分别产生会话密钥, 使双方都能持有相同的会话密钥

2. 产生X25519的key对(私钥/公钥)时, 产生私钥时, 可以随机产生. 这个私钥是为会话准备的, 然后根据会话私钥产生会话公钥.
然后交换公钥给对方, 并分别产生会话密钥, 使双方都能持有相同的会话密钥

可以看到case2更安全, 密钥不在程序中定义.
*/

/*
 * Copyright 2022-2023 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include 
#include 
#include 
#include 

#include "my_openSSL_lib.h"

 /*
  * This is a demonstration of key exchange using X25519.
  *
  * The variables beginning `peer1_` / `peer2_` are data which would normally be
  * accessible to that peer.
  *
  * Ordinarily you would use random keys, which are demonstrated
  * below when use_kat=0. A known answer test is demonstrated
  * when use_kat=1.
  */

  /* A property query used for selecting the X25519 implementation. */
static const char* propq = NULL;

static const unsigned char peer1_privk_data[32] = {
	0x80, 0x5b, 0x30, 0x20, 0x25, 0x4a, 0x70, 0x2c,
	0xad, 0xa9, 0x8d, 0x7d, 0x47, 0xf8, 0x1b, 0x20,
	0x89, 0xd2, 0xf9, 0x14, 0xac, 0x92, 0x27, 0xf2,
	0x10, 0x7e, 0xdb, 0x21, 0xbd, 0x73, 0x73, 0x5d
};

static const unsigned char peer2_privk_data[32] = {
	0xf8, 0x84, 0x19, 0x69, 0x79, 0x13, 0x0d, 0xbd,
	0xb1, 0x76, 0xd7, 0x0e, 0x7e, 0x0f, 0xb6, 0xf4,
	0x8c, 0x4a, 0x8c, 0x5f, 0xd8, 0x15, 0x09, 0x0a,
	0x71, 0x78, 0x74, 0x92, 0x0f, 0x85, 0xc8, 0x43
};

static const unsigned char expected_result[32] = {
	0x19, 0x71, 0x26, 0x12, 0x74, 0xb5, 0xb1, 0xce,
	0x77, 0xd0, 0x79, 0x24, 0xb6, 0x0a, 0x5c, 0x72,
	0x0c, 0xa6, 0x56, 0xc0, 0x11, 0xeb, 0x43, 0x11,
	0x94, 0x3b, 0x01, 0x45, 0xca, 0x19, 0xfe, 0x09
};

typedef struct peer_data_st {
	const char* name;               /* name of peer */
	EVP_PKEY* privk;                /* privk generated for peer */
	unsigned char pubk_data[32];    /* generated pubk to send to other peer */

	unsigned char* secret;          /* allocated shared secret buffer */
	size_t secret_len;
} PEER_DATA;

/*
 * Prepare for X25519 key exchange. The public key to be sent to the remote peer
 * is put in pubk_data, which should be a 32-byte buffer. Returns 1 on success.
 */
static int keyexch_x25519_before(
	OSSL_LIB_CTX* libctx,
	const unsigned char* kat_privk_data,
	PEER_DATA* local_peer)
{
	int ret = 0;
	size_t pubk_data_len = 0;

	/* Generate or load X25519 key for the peer */
	if (kat_privk_data != NULL)
		local_peer->privk =
		EVP_PKEY_new_raw_private_key_ex(libctx, "X25519", propq,
			kat_privk_data,
			sizeof(peer1_privk_data));
	else
		local_peer->privk = EVP_PKEY_Q_keygen(libctx, propq, "X25519");

	if (local_peer->privk == NULL) {
		fprintf(stderr, "Could not load or generate private key\n");
		goto end;
	}

	/* Get public key corresponding to the private key */
	if (EVP_PKEY_get_octet_string_param(local_peer->privk,
		OSSL_PKEY_PARAM_PUB_KEY,
		local_peer->pubk_data,
		sizeof(local_peer->pubk_data),
		&pubk_data_len) == 0) {
		fprintf(stderr, "EVP_PKEY_get_octet_string_param() failed\n");
		goto end;
	}

	/* X25519 public keys are always 32 bytes */
	if (pubk_data_len != 32) {
		fprintf(stderr, "EVP_PKEY_get_octet_string_param() "
			"yielded wrong length\n");
		goto end;
	}

	ret = 1;
end:
	if (ret == 0) {
		EVP_PKEY_free(local_peer->privk);
		local_peer->privk = NULL;
	}

	return ret;
}

/*
 * Complete X25519 key exchange. remote_peer_pubk_data should be the 32 byte
 * public key value received from the remote peer. On success, returns 1 and the
 * secret is pointed to by *secret. The caller must free it.
 */
static int keyexch_x25519_after(
	OSSL_LIB_CTX* libctx,
	int use_kat,
	PEER_DATA* local_peer,
	const unsigned char* remote_peer_pubk_data)
{
	int ret = 0;
	EVP_PKEY* remote_peer_pubk = NULL;
	EVP_PKEY_CTX* ctx = NULL;

	local_peer->secret = NULL;

	/* Load public key for remote peer. */
	remote_peer_pubk =
		EVP_PKEY_new_raw_public_key_ex(libctx, "X25519", propq,
			remote_peer_pubk_data, 32);
	if (remote_peer_pubk == NULL) {
		fprintf(stderr, "EVP_PKEY_new_raw_public_key_ex() failed\n");
		goto end;
	}

	/* Create key exchange context. */
	ctx = EVP_PKEY_CTX_new_from_pkey(libctx, local_peer->privk, propq);
	if (ctx == NULL) {
		fprintf(stderr, "EVP_PKEY_CTX_new_from_pkey() failed\n");
		goto end;
	}

	/* Initialize derivation process. */
	if (EVP_PKEY_derive_init(ctx) == 0) {
		fprintf(stderr, "EVP_PKEY_derive_init() failed\n");
		goto end;
	}

	/* Configure each peer with the other peer's public key. */
	if (EVP_PKEY_derive_set_peer(ctx, remote_peer_pubk) == 0) {
		fprintf(stderr, "EVP_PKEY_derive_set_peer() failed\n");
		goto end;
	}

	/* Determine the secret length. */
	if (EVP_PKEY_derive(ctx, NULL, &local_peer->secret_len) == 0) {
		fprintf(stderr, "EVP_PKEY_derive() failed\n");
		goto end;
	}

	/*
	 * We are using X25519, so the secret generated will always be 32 bytes.
	 * However for exposition, the code below demonstrates a generic
	 * implementation for arbitrary lengths.
	 */
	if (local_peer->secret_len != 32) { /* unreachable */
		fprintf(stderr, "Secret is always 32 bytes for X25519\n");
		goto end;
	}

	/* Allocate memory for shared secrets. */
	local_peer->secret = OPENSSL_malloc(local_peer->secret_len);
	if (local_peer->secret == NULL) {
		fprintf(stderr, "Could not allocate memory for secret\n");
		goto end;
	}

	/* Derive the shared secret. */
	if (EVP_PKEY_derive(ctx, local_peer->secret,
		&local_peer->secret_len) == 0) {
		fprintf(stderr, "EVP_PKEY_derive() failed\n");
		goto end;
	}

	printf("Shared secret (%s):\n", local_peer->name);
	BIO_dump_indent_fp(stdout, local_peer->secret, (int)local_peer->secret_len, 2);
	putchar('\n');

	ret = 1;
end:
	EVP_PKEY_CTX_free(ctx);
	EVP_PKEY_free(remote_peer_pubk);
	if (ret == 0) {
		OPENSSL_clear_free(local_peer->secret, local_peer->secret_len);
		local_peer->secret = NULL;
	}

	return ret;
}

static int keyexch_x25519(int use_kat)
{
	int ret = 0;
	OSSL_LIB_CTX* libctx = NULL;
	PEER_DATA peer1 = { "peer 1" }, peer2 = { "peer 2" };

	/*
	 * Each peer generates its private key and sends its public key
	 * to the other peer. The private key is stored locally for
	 * later use.
	 */
	if (keyexch_x25519_before(libctx, use_kat ? peer1_privk_data : NULL,
		&peer1) == 0)
		return 0;

	if (keyexch_x25519_before(libctx, use_kat ? peer2_privk_data : NULL,
		&peer2) == 0)
		return 0;

	/*
	 * Each peer uses the other peer's public key to perform key exchange.
	 * After this succeeds, each peer has the same secret in its
	 * PEER_DATA.
	 */
	if (keyexch_x25519_after(libctx, use_kat, &peer1, peer2.pubk_data) == 0)
		return 0;

	if (keyexch_x25519_after(libctx, use_kat, &peer2, peer1.pubk_data) == 0)
		return 0;

	/*
	 * Here we demonstrate the secrets are equal for exposition purposes.
	 *
	 * Although in practice you will generally not need to compare secrets
	 * produced through key exchange, if you do compare cryptographic secrets,
	 * always do so using a constant-time function such as CRYPTO_memcmp, never
	 * using memcmp(3).
	 */
	if (CRYPTO_memcmp(peer1.secret, peer2.secret, peer1.secret_len) != 0) {
		fprintf(stderr, "Negotiated secrets do not match\n");
		goto end;
	}

	/* If we are doing the KAT, the secret should equal our reference result. */
	if (use_kat && CRYPTO_memcmp(peer1.secret, expected_result,
		peer1.secret_len) != 0) {
		fprintf(stderr, "Did not get expected result\n");
		goto end;
	}

	ret = 1;
end:
	/* The secrets are sensitive, so ensure they are erased before freeing. */
	OPENSSL_clear_free(peer1.secret, peer1.secret_len);
	OPENSSL_clear_free(peer2.secret, peer2.secret_len);

	EVP_PKEY_free(peer1.privk);
	EVP_PKEY_free(peer2.privk);
	OSSL_LIB_CTX_free(libctx);
	return ret;
}

int main(int argc, char** argv)
{
	/* Test X25519 key exchange with known result. */
	printf("Key exchange using known answer (deterministic):\n");
	if (keyexch_x25519(1) == 0)
		return EXIT_FAILURE;

	/* Test X25519 key exchange with random keys. */
	printf("Key exchange using random keys:\n");
	if (keyexch_x25519(0) == 0)
		return EXIT_FAILURE;

	return EXIT_SUCCESS;
}

END