关于RSA加密算法的长度问题

RSA是常用的非对称加密算法。近来有学生在项目中使用System.Security类库中的RSA加密算法时，出现了“不正确的长度”，这实际上是因为待加密的数据超长所致。.net

Framework中提供的RSA算法规定，每次加密的字节数，不能超过密钥的长度值减去11,而每次加密得到的密文长度，却恰恰是密钥的长度。所以，如果要加密较长的数据，可以采用数据截取的方法，分段加密。或者增加自定义分块算法，进行加密。当然，你也可以加长密钥的长度，呵呵。下面是分段加解密代码片段，希望对程序媛们有帮助

public override byte[] Encrypt(byte[] sourceBytes)
{
CspParameters cspParams = new CspParameters();
cspParams.KeyContainerName = KeyContainerName;
RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(cspParams);

int keySize = RSAalg.KeySize / 8;
int bufferSize = keySize - 11;
byte[] buffer = new  byte[bufferSize];
MemoryStream msInput = new MemoryStream(sourceBytes);
MemoryStream msOutput = new MemoryStream();
int readLen = msInput.Read(buffer, 0, bufferSize);
while (readLen > 0)
{

byte[] dataToEnc = new byte[readLen];

Array.Copy(buffer, 0, dataToEnc, 0, readLen);

byte[] encData = RSAalg.Encrypt(dataToEnc, false);

msOutput.Write(encData, 0, encData.Length);

readLen = msInput.Read(buffer, 0, bufferSize);

}

msInput.Close();

byte[] result = msOutput.ToArray();     //得到加密结果

msOutput.Close();

RSAalg.Clear();

return result;

//return RSAalg.Encrypt(sourceBytes, false);
}

public override byte[] Decrypt(byte[] cryptBytes)
{
CspParameters cspParams = new CspParameters();
cspParams.KeyContainerName = KeyContainerName;
RSACryptoServiceProvider RSAalg = new RSACryptoServiceProvider(cspParams);
//return RSAalg.Decrypt(cryptBytes, false);
int keySize = RSAalg.KeySize / 8;
int bufferSize = keySize;// keySize - 11;
byte[] buffer = new byte[bufferSize];
MemoryStream msInput = new MemoryStream(cryptBytes);
MemoryStream msOutput = new MemoryStream();
int readLen = msInput.Read(buffer, 0, bufferSize);
while (readLen > 0)
{

byte[] dataToDec = new byte[readLen];

Array.Copy(buffer, 0, dataToDec, 0, readLen);

byte[] decData = RSAalg.Decrypt(dataToDec, false);

msOutput.Write(decData, 0, decData.Length);

readLen = msInput.Read(buffer, 0, bufferSize);

}

msInput.Close();

byte[] result = msOutput.ToArray();     //得到加密结果

msOutput.Close();

RSAalg.Clear();

return result;
}