c# - 如何正确且一致地从字符串中获取字节以进行 AES 加密？

Question

我目前正在使用 C# 实现 AES。加密方法有两个参数:一个字符串和一个密码。我正在获取提供的字符串并将其转换为字节数组，以便稍后使用它通过 BinaryWriter 将数据写入流。

问题是，当我使用 Convert.FromBase64String(string) 时，我得到 FormatException: Invalid length. 并且当我使用 Encoding.UTF8.GetBytes( string) 我的解密方法抛出无效 PKCS7.Padding 异常。

最近几天我一直在努力解决这个问题。我在 stackoverflow.com 和其他网站上阅读了近乎无限的问题，但我仍然不知道解决这个问题的最可靠方法是什么。

将在此程序中使用的字符串仅限于句子(例如“要加密的东西”)和数字(例如“12345”)。

提前谢谢你，这是我此时的代码:

    public class AESProvider {

    public byte[] EncryptStringToBytes_Aes(string plainText, string Key)
    {
        // Check arguments. 
        if (plainText == null || plainText.Length <= 0)
            throw new ArgumentNullException("plainText");
        if (Key == null || Key.Length <= 0)
            throw new ArgumentNullException("Key");
        byte[] plainTextInBytes = Convert.FromBase64String(plainText);
        byte[] encrypted;

        //Create an Aes object
        //with the specified key and IV.

        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.GenerateIV();
            byte[] IV = aesAlg.IV;
            //The Salt will be the first 8 bytes of the IV.
            byte[] theSalt = new byte[8];
            Array.Copy(IV,theSalt,8);
            //A key for AES is generated by expanding the password using the following method.
            Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
            byte[] aesKey = keyGen.GetBytes(16);
            aesAlg.Key = aesKey;

            // Create a decrytor to perform the stream transform.
            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, IV);

            // Create the streams used for encryption. 
            using (MemoryStream msEncrypt = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using (BinaryWriter swEncrypt = new BinaryWriter(csEncrypt))
                    {

                        //Write all data to the stream.
                        swEncrypt.Write(plainTextInBytes);
                    }
                    encrypted = msEncrypt.ToArray();
                }
            }
            // Prepend the IV to the ciphertext so it can be used in the decryption process.
            using (MemoryStream ivPlusCipher = new MemoryStream())
            {
                using (BinaryWriter tBinaryWriter = new BinaryWriter(ivPlusCipher))
                {
                    tBinaryWriter.Write(IV);
                    tBinaryWriter.Write(encrypted);
                    tBinaryWriter.Flush();
                }
                return ivPlusCipher.ToArray();
            }
        }
    }

    public byte[] DecryptStringFromBytes_Aes(byte[] cipherText, string Key)
    {
        // Check arguments. 
        if (cipherText == null || cipherText.Length <= 0)
            throw new ArgumentNullException("cipherText");
        if (Key == null || Key.Length <= 0)
            throw new ArgumentNullException("Key");
        // Declare the string used to hold 
        // the decrypted text. 
        byte[] decrypted;

        // Create an Aes object 
        // with the specified key and IV. 

        // Create the streams used for decryption. 

        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;
            //Grab IV from ciphertext
            byte[] IV = new byte[16];
            Array.Copy(cipherText,0,IV,0,16);
            //Use the IV for the Salt
            byte[] theSalt = new byte[8];
            Array.Copy(IV,theSalt,8);
            Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
            byte[] aesKey = keyGen.GetBytes(16);
            aesAlg.Key = aesKey;

            // Create a decrytor to perform the stream transform.
            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, IV);

            using (MemoryStream msDecrypt = new MemoryStream())
            {
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write))
                {
                    using (BinaryWriter srDecrypt = new BinaryWriter(csDecrypt))
                    {
                        //Decrypt the ciphertext
                        srDecrypt.Write(cipherText, IV.Length, (cipherText.Length - IV.Length));
                    }
                    decrypted = msDecrypt.ToArray();
                    return decrypted;
                }
            }   
        }
    }
}

Answer 1

您需要在加密/解密前后进行字节和字符串之间的转换。这不是同一个操作，你不应该使用同一个方法。

加密时，您从任意字符串开始。使用 Encoding.UTF8.GetBytes() 将其转换为 byte[]。加密它。现在可以使用 Convert.ToBase64String() 将生成的 byte[] 转换为字符串。

解密时，您现在从 Base64 编码的字符串开始。使用 Convert.FromBase64String() 将其解码为 byte[]。解密它。您现在拥有原始字符串的 UTF-8 编码，您可以使用 Encoding.UTF8.GetString() 对其进行解码。

记住:

• Encoding.UTF8 可将任意字符串转换为字节数组(但它只能将包含实际 UTF8 编码的字节数组转换回来)。
• Convert.[To/From]Base64String 可将任意字节数组转换为字符串(但它只能将包含实际 Base64 编码的字符串转换回来)。