RSA不限长度非对称加密解密C#

RSA 分段加解密【解决“不正确的长度”的异常】

　　RSA 是常用的非对称加密算法。最近使用时却出现了“不正确的长度”的异常，研究发现是由于待加密的数据超长所致。

　　.NET Framework 中提供的 RSA 算法规定：

　　待加密的字节数不能超过密钥的长度值除以 8 再减去 11（即：RSACryptoServiceProvider.KeySize / 8 - 11），而加密后得到密文的字节数，正好是密钥的长度值除以 8（即：RSACryptoServiceProvider.KeySize / 8）。

　　所以，如果要加密较长的数据，则可以采用分段加解密的方式，实现方式如下：

namespace Macroresolute.RSACryptoService
{
public static class RSACrypto
{
private static readonly Encoding Encoder = Encoding.UTF8;

public static String Encrypt(this String plaintext)
{
X509Certificate2 _X509Certificate2 = RSACrypto.RetrieveX509Certificate();
using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PublicKey.Key as RSACryptoServiceProvider)
{
Byte[] PlaintextData = RSACrypto.Encoder.GetBytes(plaintext);
int MaxBlockSize = RSACryptography.KeySize / 8 - 11;    //加密块最大长度限制

if (PlaintextData.Length <= MaxBlockSize)
return Convert.ToBase64String(RSACryptography.Encrypt(PlaintextData, false));

using (MemoryStream PlaiStream = new MemoryStream(PlaintextData))
using (MemoryStream CrypStream = new MemoryStream())
{
Byte[] Buffer = new Byte[MaxBlockSize];
int BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);

while (BlockSize > 0)
{
Byte[] ToEncrypt = new Byte[BlockSize];
Array.Copy(Buffer, 0, ToEncrypt, 0, BlockSize);

Byte[] Cryptograph = RSACryptography.Encrypt(ToEncrypt, false);
CrypStream.Write(Cryptograph, 0, Cryptograph.Length);

BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
}

return Convert.ToBase64String(CrypStream.ToArray(), Base64FormattingOptions.None);
}
}
}

public static String Decrypt(this String ciphertext)
{
X509Certificate2 _X509Certificate2 = RSACrypto.RetrieveX509Certificate();
using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PrivateKey as RSACryptoServiceProvider)
{
Byte[] CiphertextData = Convert.FromBase64String(ciphertext);
int MaxBlockSize = RSACryptography.KeySize / 8;    //解密块最大长度限制

if (CiphertextData.Length <= MaxBlockSize)
return RSACrypto.Encoder.GetString(RSACryptography.Decrypt(CiphertextData, false));

using (MemoryStream CrypStream = new MemoryStream(CiphertextData))
using (MemoryStream PlaiStream = new MemoryStream())
{
Byte[] Buffer = new Byte[MaxBlockSize];
int BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);

while (BlockSize > 0)
{
Byte[] ToDecrypt = new Byte[BlockSize];
Array.Copy(Buffer, 0, ToDecrypt, 0, BlockSize);

Byte[] Plaintext = RSACryptography.Decrypt(ToDecrypt, false);
PlaiStream.Write(Plaintext, 0, Plaintext.Length);

BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
}

return RSACrypto.Encoder.GetString(PlaiStream.ToArray());
}
}
}

private static X509Certificate2 RetrieveX509Certificate()
{
return null;    //检索用于 RSA 加密的 X509Certificate2 证书
}
}
}

注：以上加密方法返回的字符串类型为原始的 Base-64 ，若要用于 URL 传输，需另行处理！

　　以上文章转载自/article/5403876.html

　　下面是自己修改

　　如果没有证书请用以下方法

/// <summary>
///
/// </summary>
public class RSADecryptEncrypt
{

private static readonly Encoding Encoder = Encoding.UTF8;
/// <summary>
/// 公钥加密
/// </summary>
/// <param name="xmlPublicKey">公钥</param>
/// <param name="EncryptString">加密字符串</param>
/// <returns></returns>
public static String Encrypt(string xmlPublicKey, string EncryptString)
{
using (RSACryptoServiceProvider RSACryptography = new RSACryptoServiceProvider())
{

RSACryptography.FromXmlString(xmlPublicKey);
Byte[] PlaintextData = RSADecryptEncrypt.Encoder.GetBytes(EncryptString);
int MaxBlockSize = RSACryptography.KeySize / 8 - 11;//加密块最大长度限制

if (PlaintextData.Length <= MaxBlockSize)
return Convert.ToBase64String(RSACryptography.Encrypt(PlaintextData, false));

using (MemoryStream PlaiStream = new MemoryStream(PlaintextData))
using (MemoryStream CrypStream = new MemoryStream())
{
Byte[] Buffer = new Byte[MaxBlockSize];
int BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);

while (BlockSize > 0)
{
Byte[] ToEncrypt = new Byte[BlockSize];
Array.Copy(Buffer, 0, ToEncrypt, 0, BlockSize);

Byte[] Cryptograph = RSACryptography.Encrypt(ToEncrypt, false);
CrypStream.Write(Cryptograph, 0, Cryptograph.Length);

BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
}

return Convert.ToBase64String(CrypStream.ToArray(), Base64FormattingOptions.None);
}
}
}

/// <summary>
/// 解密
/// </summary>
/// <param name="xmlPublicKey"></param>
/// <param name="EncryptString"></param>
/// <returns></returns>
public static String Decrypt(string xmlPrivateKey, string EncryptString)
{
using (RSACryptoServiceProvider RSACryptography = new RSACryptoServiceProvider())
{
RSACryptography.FromXmlString(xmlPrivateKey);
Byte[] CiphertextData = Convert.FromBase64String(EncryptString);
int MaxBlockSize = RSACryptography.KeySize / 8;    //解密块最大长度限制

if (CiphertextData.Length <= MaxBlockSize)
return RSADecryptEncrypt.Encoder.GetString(RSACryptography.Decrypt(CiphertextData, false));

using (MemoryStream CrypStream = new MemoryStream(CiphertextData))
using (MemoryStream PlaiStream = new MemoryStream())
{
Byte[] Buffer = new Byte[MaxBlockSize];
int BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);

while (BlockSize > 0)
{
Byte[] ToDecrypt = new Byte[BlockSize];
Array.Copy(Buffer, 0, ToDecrypt, 0, BlockSize);

Byte[] Plaintext = RSACryptography.Decrypt(ToDecrypt, false);
PlaiStream.Write(Plaintext, 0, Plaintext.Length);

BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
}

return RSADecryptEncrypt.Encoder.GetString(PlaiStream.ToArray());
}
}
}

}