可以使用vc6.0运行的RSA数字签名C++代码

当然可以，下面是一个使用VC6.0编译运行的RSA数字签名C++代码示例：

#include <iostream>
#include <openssl/rsa.h>
#include <openssl/pem.h>

using namespace std;

// RSA数字签名
int rsa_sign(const char* data, int data_len, const char* private_key_file, unsigned char* signature)
{
    // 读取私钥文件
    FILE* fp = fopen(private_key_file, "r");
    if (fp == NULL) {
        cout << "Failed to open private key file!" << endl;
        return -1;
    }
    RSA* rsa = PEM_read_RSAPrivateKey(fp, NULL, NULL, NULL);
    fclose(fp);

    if (rsa == NULL) {
        cout << "Failed to read private key!" << endl;
        return -1;
    }

    // 计算签名
    int signature_len = RSA_size(rsa);
    if (RSA_sign(NID_sha1, (unsigned char*)data, data_len, signature, (unsigned int*)&signature_len, rsa) != 1) {
        cout << "Failed to sign data!" << endl;
        RSA_free(rsa);
        return -1;
    }
    RSA_free(rsa);

    return signature_len;
}

int main()
{
    const char* data = "Hello, world!";
    const char* private_key_file = "private_key.pem";
    unsigned char signature[1024] = { 0 };

    int signature_len = rsa_sign(data, strlen(data), private_key_file, signature);
    if (signature_len == -1) {
        cout << "Failed to sign data!" << endl;
        return -1;
    }

    cout << "Signature: ";
    for (int i = 0; i < signature_len; i++) {
        printf("%02x", signature[i]);
    }
    cout << endl;

    system("pause");
    return 0;
}

注意：VC6.0需要安装OpenSSL库，需要在工程设置中添加libcrypto.lib库文件并添加头文件路径。另外，在VC6.0中需要使用printf函数代替cout输出十六进制数。