在 .NET 中使用 AES 加密 - CryptographicException 表示填

问题描述

我用 C# 编写了一些 AES 加密代码，但无法正确加密和解​​密.如果我输入test"作为密码并且这个数据必须对所有人保密！"我收到以下异常:

I wrote some AES encryption code in C# and I am having trouble getting it to encrypt and decrypt properly. If I enter "test" as the passphrase and "This data must be kept secret from everyone!" I receive the following exception:

System.Security.Cryptography.CryptographicException: Padding is invalid and cannot be removed.
   at System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32 outputOffset, PaddingMode paddingMode, Boolean fLast)
   at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
   at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
   at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)
   at System.IO.Stream.Close()
   at System.IO.Stream.Dispose()
   ...

如果我输入的内容少于 16 个字符，我不会得到任何输出.

And if I enter something less than 16 characters I get no output.

我认为我需要在加密中进行一些特殊处理，因为 AES 是一种分组密码，但我不确定那是什么，而且我无法在网络上找到任何示例来说明如何操作.这是我的代码:

I believe I need some special handling in the encryption since AES is a block cipher, but I'm not sure exactly what that is, and I wasn't able to find any examples on the web showing how. Here is my code:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public static class DatabaseCrypto
{
    public static EncryptedData Encrypt(string password, string data)
    {
        return DatabaseCrypto.Transform(true, password, data, null, null) as EncryptedData;
    }

    public static string Decrypt(string password, EncryptedData data)
    {
        return DatabaseCrypto.Transform(false, password, data.DataString, data.SaltString, data.MACString) as string;
    }

    private static object Transform(bool encrypt, string password, string data, string saltString, string macString)
    {
        using (AesManaged aes = new AesManaged())
        {
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;
            int key_len = aes.KeySize / 8;
            int iv_len = aes.BlockSize / 8;
            const int salt_size = 8;
            const int iterations = 8192;

            byte[] salt = encrypt ? new byte[salt_size] : Convert.FromBase64String(saltString);
            if (encrypt)
            {
                new RNGCryptoServiceProvider().GetBytes(salt);
            }

            byte[] bc_key = new Rfc2898DeriveBytes("BLK" + password, salt, iterations).GetBytes(key_len);
            byte[] iv = new Rfc2898DeriveBytes("IV" + password, salt, iterations).GetBytes(iv_len);
            byte[] mac_key = new Rfc2898DeriveBytes("MAC" + password, salt, iterations).GetBytes(16);

            aes.Key = bc_key;
            aes.IV = iv;

            byte[] rawData = encrypt ? Encoding.UTF8.GetBytes(data) : Convert.FromBase64String(data);

            using (ICryptoTransform transform = encrypt ? aes.CreateEncryptor() : aes.CreateDecryptor())
            using (MemoryStream memoryStream = encrypt ? new MemoryStream() : new MemoryStream(rawData))
            using (CryptoStream cryptoStream = new CryptoStream(memoryStream, transform, encrypt ? CryptoStreamMode.Write : CryptoStreamMode.Read))
            {
                if (encrypt)
                {
                    cryptoStream.Write(rawData, 0, rawData.Length);

                    return new EncryptedData(salt, mac_key, memoryStream.ToArray());
                }
                else
                {
                    byte[] originalData = new byte[rawData.Length];
                    int count = cryptoStream.Read(originalData, 0, originalData.Length);

                    return Encoding.UTF8.GetString(originalData, 0, count);
                }
            }
        }
    }
}

public class EncryptedData
{
    public EncryptedData()
    {
    }

    public EncryptedData(byte[] salt, byte[] mac, byte[] data)
    {
        this.Salt = salt;
        this.MAC = mac;
        this.Data = data;
    }

    public EncryptedData(string salt, string mac, string data)
    {
        this.SaltString = salt;
        this.MACString = mac;
        this.DataString = data;
    }

    public byte[] Salt
    {
        get;
        set;
    }

    public string SaltString
    {
        get { return Convert.ToBase64String(this.Salt); }
        set { this.Salt = Convert.FromBase64String(value); }
    }

    public byte[] MAC
    {
        get;
        set;
    }

    public string MACString
    {
        get { return Convert.ToBase64String(this.MAC); }
        set { this.MAC = Convert.FromBase64String(value); }
    }

    public byte[] Data
    {
        get;
        set;
    }

    public string DataString
    {
        get { return Convert.ToBase64String(this.Data); }
        set { this.Data = Convert.FromBase64String(value); }
    }
}

    static void ReadTest()
    {
        Console.WriteLine("Enter password: ");
        string password = Console.ReadLine();

        using (StreamReader reader = new StreamReader("aes.cs.txt"))
        {
            EncryptedData enc = new EncryptedData();
            enc.SaltString = reader.ReadLine();
            enc.MACString = reader.ReadLine();
            enc.DataString = reader.ReadLine();

            Console.WriteLine("The decrypted data was: " + DatabaseCrypto.Decrypt(password, enc));
        }
    }

    static void WriteTest()
    {
        Console.WriteLine("Enter data: ");
        string data = Console.ReadLine();
        Console.WriteLine("Enter password: ");
        string password = Console.ReadLine();

        EncryptedData enc = DatabaseCrypto.Encrypt(password, data);

        using (StreamWriter stream = new StreamWriter("aes.cs.txt"))
        {
            stream.WriteLine(enc.SaltString);
            stream.WriteLine(enc.MACString);
            stream.WriteLine(enc.DataString);

            Console.WriteLine("The encrypted data was: " + enc.DataString);
        }
    }

推荐答案

在需要填充的模式(如 CBC)中使用像 AES 这样的分组密码时，您必须注意输出始终是分组大小的倍数.为了实现这一点，像 PKCS7 这样的填充模式将在加密过程结束时向密码添加一些字节.但是你必须让加密器知道何时结束.为此，您所要做的就是插入语句

When using a block cipher like AES in a mode that requires padding, like CBC, you must be aware that the output will always be a multiple of the block size. To accomplish this, padding modes like PKCS7 will add some bytes to the cipher at the end of the encryption process. But you have to let the encryptor know when the end occurs. To do so, all you have to do is insert the statement

cryptoStream.FlushFinalBlock();  

之后

cryptoStream.Write(rawData, 0, rawData.Length);

PS:

也许它只是为了调试，但你的盐生成方法每次都会生成完全相同的盐.

Perhaps it is just for debugging, but your salt generation method generates the exact same salt every time.

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