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  • 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
                }
            }
        }

    :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!

    分享自:http://www.cnblogs.com/zys529/archive/2012/05/24/2516539.html

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  • 原文地址:https://www.cnblogs.com/JuneZhang/p/7298058.html
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