在C#中通过JS发布解密RSA公钥加密数据

Question

在C#中解密RSA加密字符串时，我得到的错误是，要解密的数据超过了256字节模的最大值。

我正在努力实现的目标：

1. 在C#（RSA）中生成公钥/私钥对
2. 将私钥保存在会话/临时存储中，以便在解密期间使用
3. 向客户端/JS发送/返回公钥以用于加密
4. 用公钥加密JS中的字符串（最多20个字符）并发送到服务器
5. 使用步骤2中保存的私钥解密服务器中加密的字符串

工作原理：

1. 公钥/私钥对的生成
2. 在JS中使用库jscrypt进行加密

目前编写的代码：

C类#

    ///Source: https://stackoverflow.com/questions/17128038/c-sharp-rsa-encryption-decryption-with-transmission
    public static void GenerateKeys()
    {
        //CSP with a new 2048 bit rsa key pair
        var csp = new RSACryptoServiceProvider(2048);

        //Private key
        var privKey = csp.ExportParameters(true);

        //Public key
        var pubKey = csp.ExportParameters(false);

        string privKeyString = string.Empty;

        var sw = new System.IO.StringWriter();
        var xs = new System.Xml.Serialization.XmlSerializer(typeof(RSAParameters));
        xs.Serialize(sw, privKey);
        privKeyString = sw.ToString();

        //This will give public key in the following format which is required by the JS library
        //-----BEGIN PUBLIC KEY-----
        //XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
        //-----END PUBLIC KEY-----
        string publicKeyBase64 = ConvertPublicKeyForJS(pubKey);

        //Will be saved in sesssion for later use during decryption
        string privateKeyBase64 = Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(privKeyString));

        //Save in session/temp location
        //Return publicKeyBase64 to JS
    }

    /// <summary>
    /// Source: https://stackoverflow.com/questions/28406888/c-sharp-rsa-public-key-output-not-correct/28407693#28407693
    /// </summary>
    /// <param name="publicKey"></param>
    /// <returns></returns>
    public static string ConvertPublicKeyForJS(RSAParameters publicKey)
    {
        string output = string.Empty;

        using (var stream = new MemoryStream())
        {
            var writer = new BinaryWriter(stream);
            writer.Write((byte)0x30); // SEQUENCE
            using (var innerStream = new MemoryStream())
            {
                var innerWriter = new BinaryWriter(innerStream);
                innerWriter.Write((byte)0x30); // SEQUENCE
                EncodeLength(innerWriter, 13);
                innerWriter.Write((byte)0x06); // OBJECT IDENTIFIER
                var rsaEncryptionOid = new byte[] { 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01 };
                EncodeLength(innerWriter, rsaEncryptionOid.Length);
                innerWriter.Write(rsaEncryptionOid);
                innerWriter.Write((byte)0x05); // NULL
                EncodeLength(innerWriter, 0);
                innerWriter.Write((byte)0x03); // BIT STRING
                using (var bitStringStream = new MemoryStream())
                {
                    var bitStringWriter = new BinaryWriter(bitStringStream);
                    bitStringWriter.Write((byte)0x00); // # of unused bits
                    bitStringWriter.Write((byte)0x30); // SEQUENCE
                    using (var paramsStream = new MemoryStream())
                    {
                        var paramsWriter = new BinaryWriter(paramsStream);
                        EncodeIntegerBigEndian(paramsWriter, publicKey.Modulus); // Modulus
                        EncodeIntegerBigEndian(paramsWriter, publicKey.Exponent); // Exponent
                        var paramsLength = (int)paramsStream.Length;
                        EncodeLength(bitStringWriter, paramsLength);
                        bitStringWriter.Write(paramsStream.GetBuffer(), 0, paramsLength);
                    }
                    var bitStringLength = (int)bitStringStream.Length;
                    EncodeLength(innerWriter, bitStringLength);
                    innerWriter.Write(bitStringStream.GetBuffer(), 0, bitStringLength);
                }
                var length = (int)innerStream.Length;
                EncodeLength(writer, length);
                writer.Write(innerStream.GetBuffer(), 0, length);
            }

            var base64 = Convert.ToBase64String(stream.GetBuffer(), 0, (int)stream.Length);

            StringBuilder sb = new StringBuilder();
            sb.AppendLine("-----BEGIN PUBLIC KEY-----");
            sb.AppendLine(base64);
            sb.AppendLine("-----END PUBLIC KEY-----");

            output = sb.ToString();
        }

        return output;
    }

    private static void EncodeLength(BinaryWriter stream, int length)
    {
        if (length < 0) throw new ArgumentOutOfRangeException("length", "Length must be non-negative");
        if (length < 0x80)
        {
            // Short form
            stream.Write((byte)length);
        }
        else
        {
            // Long form
            var temp = length;
            var bytesRequired = 0;
            while (temp > 0)
            {
                temp >>= 8;
                bytesRequired++;
            }
            stream.Write((byte)(bytesRequired | 0x80));
            for (var i = bytesRequired - 1; i >= 0; i--)
            {
                stream.Write((byte)(length >> (8 * i) & 0xff));
            }
        }
    }

    private static void EncodeIntegerBigEndian(BinaryWriter stream, byte[] value, bool forceUnsigned = true)
    {
        stream.Write((byte)0x02); // INTEGER
        var prefixZeros = 0;
        for (var i = 0; i < value.Length; i++)
        {
            if (value[i] != 0) break;
            prefixZeros++;
        }
        if (value.Length - prefixZeros == 0)
        {
            EncodeLength(stream, 1);
            stream.Write((byte)0);
        }
        else
        {
            if (forceUnsigned && value[prefixZeros] > 0x7f)
            {
                // Add a prefix zero to force unsigned if the MSB is 1
                EncodeLength(stream, value.Length - prefixZeros + 1);
                stream.Write((byte)0);
            }
            else
            {
                EncodeLength(stream, value.Length - prefixZeros);
            }
            for (var i = prefixZeros; i < value.Length; i++)
            {
                stream.Write(value[i]);
            }
        }
    }

    public static string DecryptValue(string cypherText)
    {
        string plainTextData = string.Empty;

        string privKeyBase64 = ""; //get value from session/temp storage

        string privKeyString = System.Text.Encoding.ASCII.GetString(Convert.FromBase64String(privKeyBase64));

        var sr = new System.IO.StringReader(privKeyString);
        var xs = new System.Xml.Serialization.XmlSerializer(typeof(RSAParameters));
        var privKey = (RSAParameters)xs.Deserialize(sr);

        var csp = new RSACryptoServiceProvider();
        csp.ImportParameters(privKey);

        var bytesCypherText = Convert.FromBase64String(cypherText);

        //Problematic line
        var bytesPlainTextData = csp.Decrypt(bytesCypherText, false);

        plainTextData = System.Text.Encoding.Unicode.GetString(bytesPlainTextData);

        return plainTextData;
    }

JS

   function encrypt(msg, publicKey) {
        var jsEncrypt = new JSEncrypt();
        jsEncrypt.setPublicKey(publicKey);
        var encrypted = jsEncrypt.encrypt(msg);

        var base64result = btoa(encrypted);

        return base64result;            
    }

更新/变更：

如果我将密钥大小设为1024而不是2048，那么我得到的错误是，要解密的数据超过了128字节模的最大值 。根据我在调试器中看到的内容，加密字符串的总字节数为172。

更新|解决方案：

1. 删除JS中的这一行，var base64result=btoa（加密） 。直接返回加密值即可

笔记：

• 请忽略不正确的方法返回类型，这仍然是一个POC，许多值正在手动填充
• 我不是安全方面的专家，所以很多代码都是从不同的来源中挑选出来的

Answer 1

您面临非对称加密的限制。对于大块数据来说，它非常慢，加密字符串大小受您使用的RSA密钥大小的限制。

RSA通常用于交换对称密钥和处理大部分数据。如果您必须对大量数据使用非对称，那么您需要将有效负载分解为较小的负载并在另一边重建。

RSA只能将数据加密到密钥大小（2048位=256字节）减去填充/标头数据（PKCS#1 v1.5 padding为11字节）的最大值。

如果如您所说，您只发送了20个字符，那么请确实使用断点进行检查，以确保您的解密函数得到的密码文本足够小。如果没有，您需要回溯并检查发送错误内容的位置。

也可能是因为RSA在JSEncrypt中的标准与RSA在C中的标准不同，这可以在这里的SO答案中看到