解决PHP RSA私钥解密“填充检查失败”：基于Hex编码的数据传输策略

<?php

class RSAHelper
{
    protected $privateKey;

    public function __construct($privateKeyPath = "private.pem")
    {
        // 确保私钥文件存在且可读
        if (!file_exists($privateKeyPath) || !is_readable($privateKeyPath)) {
            throw new RuntimeException("Private key file not found or not readable: " . $privateKeyPath);
        }
        $this->privateKey = @file_get_contents($privateKeyPath);
        if (empty($this->privateKey)) {
            throw new RuntimeException("Failed to load private key from: " . $privateKeyPath);
        }
    }

    /**
     * 将字符串转换为十六进制表示
     * @param string $string 待转换的字符串
     * @return string 十六进制字符串
     */
    public function toHex($string)
    {
        $hex = '';
        for ($i = 0; $i < strlen($string); $i++) {
            $hex .= dechex(ord($string[$i]));
        }
        return $hex;
    }

    /**
     * 将十六进制字符串还原为原始字符串
     * @param string $hex 十六进制字符串
     * @return string 原始字符串
     */
    public function toStr($hex)
    {
        $string = '';
        for ($i = 0; $i < strlen($hex) - 1; $i += 2) {
            $string .= chr(hexdec($hex[$i] . $hex[$i + 1]));
        }
        return $string;
    }

    /**
     * 使用私钥解密数据
     * @param string $data 经过Hex和Base64编码的加密数据
     * @return string 解密后的原始数据
     * @throws RuntimeException 如果数据无效或私钥未设置
     * @throws Exception 如果解密失败
     */
    public function decrypt($data)
    {
        if (empty($data) || !is_string($data)) {
            throw new RuntimeException('Invalid data for decryption.');
        } elseif (empty($this->privateKey)) {
            throw new RuntimeException('You need to set the private key.');
        }

        $key = openssl_get_privatekey($this->privateKey);
        if (!$key) {
            throw new Exception("Failed to load private key resource: " . openssl_error_string());
        }

        // 核心修改：先进行Hex解码，再进行Base64解码
        $decodedData = base64_decode($this->toStr($data));

        if ($decodedData === false) {
            throw new Exception("Base64 decoding failed after Hex decoding.");
        }

        $result = '';
        // 默认使用 OPENSSL_PKCS1_PADDING
        if (!openssl_private_decrypt($decodedData, $result, $key)) {
            throw new Exception("RSA decryption failed: " . openssl_error_string());
        }
        return $result;
    }
}

// 示例用法
/*
try {
    $rsa = new RSAHelper();
    // 假设 $receivedData 是从网络接收到的Hex编码后的加密字符串
    $receivedData = "7a7a7a7a..."; // 示例数据

    $decryptedMessage = $rsa->decrypt($receivedData);
    echo "Decrypted message: " . $decryptedMessage . PHP_EOL;
} catch (Exception $e) {
    echo "Error: " . $e->getMessage() . PHP_EOL;
}
*/
?>

using System;
using System.Text;
using System.Security.Cryptography; // For RSA operations if needed

public static class HexConverter
{
    /// <summary>
    /// 将字符串转换为十六进制表示
    /// </summary>
    /// <param name="str">待转换的字符串</param>
    /// <returns>十六进制字符串</returns>
    public static string ToHex(string str)
    {
        var sb = new StringBuilder();
        // 假设字符串是UTF8编码
        var bytes = Encoding.UTF8.GetBytes(str); 
        foreach (var t in bytes)
        {
            sb.Append(t.ToString("X2")); // "X2" 格式化为两位十六进制数
        }
        return sb.ToString();
    }

    /// <summary>
    /// 将十六进制字符串还原为原始字符串
    /// </summary>
    /// <param name="hexString">十六进制字符串</param>
    /// <returns>原始字符串</returns>
    public static string FromHexString(string hexString)
    {
        if (hexString.Length % 2 != 0)
        {
            throw new ArgumentException("Hex string must have an even number of characters.");
        }

        var bytes = new byte[hexString.Length / 2];
        for (var i = 0; i < bytes.Length; i++)
        {
            bytes[i] = Convert.ToByte(hexString.Substring(i * 2, 2), 16);
        }
        // 假设原始字符串是UTF8编码
        return Encoding.UTF8.GetString(bytes);
    }

    // 示例：C#中的加密流程 (假设已获得加密后的Base64字符串)
    /*
    public static string EncryptAndHexEncode(string originalData, RSAParameters publicKey)
    {
        // ... (RSA加密逻辑，生成 byte[] encryptedBytes)
        // string base64Encoded = Convert.ToBase64String(encryptedBytes);
        // string hexEncoded = ToHex(base64Encoded);
        // return hexEncoded;
    }

    // 示例：C#中的解密流程 (假设已接收到Hex编码后的字符串)
    public static string HexDecodeAndDecrypt(string hexEncodedData, RSAParameters privateKey)
    {
        string base64Encoded = FromHexString(hexEncodedData);
        byte[] encryptedBytes = Convert.FromBase64String(base64Encoded);
        // ... (RSA解密逻辑，使用 privateKey 解密 encryptedBytes)
        // return Encoding.UTF8.GetString(decryptedBytes);
    }
    */
}