在C＃中解密RSA加密的字符串时出现错误The data to be decrypted exceeds the maximum for this modulus of 256 bytes。
我要实现的目标：
有效方法：
到目前为止编写的代码：
C＃
///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/变化：
如果我将密钥大小设置为1024而不是2048，那么我得到的错误是The data to be decrypted exceeds the maximum for this modulus of 128 bytes.。根据我在调试器中看到的内容，加密字符串的总字节为172。
更新|解决方案：
var base64result = btoa(encrypted);中删除此行。只需直接返回加密值即可。var bytesPlainTextData = csp.Decrypt(bytesCypherText, false);行更改为var bytesPlainTextData = csp.Decrypt(bytesCypherText, RSAEncryptionPadding.Pkcs1);。注释：
答案 0 :(得分：2)
您面临非对称加密的限制。对于大块数据，这非常慢，并且加密字符串的大小受您使用的RSA密钥大小的限制。
RSA通常用于交换对称密钥并处理大部分数据。如果必须对大量数据使用非对称数据，则需要将有效负载分解为较小的有效负载，然后在另一侧进行重构。
RSA只能将数据加密到最大密钥大小（2048位= 256字节）减去填充/标头数据（对于PKCS＃1 v1.5填充为11字节）。
如果您只说发送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确实获得了足够小的密码文本。如果不是，则需要回溯并检查将错误的内容发送到哪里。
也可能是JSEncrypt中的RSA标准与C＃中的RSA不同，in this SO answer here