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，实现如下：
RSACryptoServiceProvider rsa = new
RSACryptoServiceProvider();
byte[] data = ........;
//要加密的数据
string publicKey = .... ; //获取公钥
rsa.FromXmlString(publicKey);
int keySize = rsa.KeySize / 8;
int bufferSize = keySize - 11;
byte[] buffer = new
byte[bufferSize];
MemoryStream msInput = new
MemoryStream(data);
MemoryStream msOuput = 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 =
rsa.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();
rsa.Clear();
解密时肯定也要使用分段解密，算法如下：
RSACryptoServiceProvider rsa = new
RSACryptoServiceProvider();
byte[] key = .....; //加载私钥
string privateKey =
Encoding.ASCII.GetString(key);
byte[] dataEnc = ...; //加载密文
rsa.FromXmlString(privateKey);
int keySize = rsa.KeySize / 8;
byte[]
buffer = new byte[keySize];
MemoryStream msInput = new
MemoryStream(dataEnc );
MemoryStream msOuput = new
MemoryStream();
int readLen = msInput.Read(buffer, 0,
keySize);
while(readLen > 0)
{
byte[] dataToDec = new
byte[readLen];
Array.Copy(buffer, 0 , dataToDec,
0, readLen);
byte[] decData =
rsa.Decrypt(dataToDec , false);
msOutput.Write(decData, 0,
decData.Length);
readLen = msInput.Read(buffer, 0,
keySize);
}
msInput.Close();
byte[] result = msOutput.ToArray();
//得到解密结果
msOutput.Close();
rsa.Clear();
