在vc++6.0中用C语言写一个ras加解密算法

以下是在VC++ 6.0中使用C语言实现RAS加解密算法的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>

int main()
{
    RSA *rsa = NULL;
    BIO *pubkeybio = NULL;
    BIO *prikeybio = NULL;
    unsigned char *msg = "Hello, world!";
    unsigned char *encrypted = NULL;
    unsigned char *decrypted = NULL;
    int encryptedlen, decryptedlen;

    // 生成RSA密钥对
    rsa = RSA_generate_key(2048, RSA_F4, NULL, NULL);
    if (rsa == NULL) {
        printf("RSA key generation failed!\n");
        exit(EXIT_FAILURE);
    }

    // 生成公钥PEM文件
    pubkeybio = BIO_new_file("public.pem", "w+");
    if (pubkeybio == NULL) {
        printf("Unable to open public key file!\n");
        exit(EXIT_FAILURE);
    }
    PEM_write_bio_RSAPublicKey(pubkeybio, rsa);
    BIO_free(pubkeybio);

    // 生成私钥PEM文件
    prikeybio = BIO_new_file("private.pem", "w+");
    if (prikeybio == NULL) {
        printf("Unable to open private key file!\n");
        exit(EXIT_FAILURE);
    }
    PEM_write_bio_RSAPrivateKey(prikeybio, rsa, NULL, NULL, 0, NULL, NULL);
    BIO_free(prikeybio);

    // 加密
    encrypted = (unsigned char *)malloc(RSA_size(rsa));
    encryptedlen = RSA_public_encrypt(strlen(msg) + 1, msg, encrypted, rsa, RSA_PKCS1_PADDING);
    if (encryptedlen == -1) {
        printf("Encryption failed!\n");
        exit(EXIT_FAILURE);
    }
    printf("Encrypted message: %s\n", encrypted);

    // 解密
    decrypted = (unsigned char *)malloc(RSA_size(rsa));
    decryptedlen = RSA_private_decrypt(encryptedlen, encrypted, decrypted, rsa, RSA_PKCS1_PADDING);
    if (decryptedlen == -1) {
        printf("Decryption failed!\n");
        exit(EXIT_FAILURE);
    }
    printf("Decrypted message: %s\n", decrypted);

    RSA_free(rsa);
    free(encrypted);
    free(decrypted);

    return 0;
}

以上代码使用OpenSSL库实现了RSA密钥对的生成、公钥和私钥的输出、加密和解密操作。在VC++ 6.0中需要在工程属性中添加OpenSSL库的链接库和头文件路径，具体方法可以参考OpenSSL的安装文档。