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 <stdio.h>
#include <string.h>
#include <openssl/core_names.h>
#include <openssl/evp.h>#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));elselocal_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