用于将字节数组转换为字符串的编码，反之亦然

Question

I use this code to encrypt a string (basically, this is the example given on the Rijndael class on MSDN ):

public static String AESEncrypt(String str2Encrypt, Byte[] encryptionKey, Byte[] IV)
{
    Byte[] encryptedText;

    using (RijndaelManaged rijAlg = new RijndaelManaged())
    {
        // Use the provided key and IV
        rijAlg.Key = encryptionKey;
        rijAlg.IV = IV;

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

        // Create the streams used for encryption
        using (MemoryStream msEncrypt = new MemoryStream())
        using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
        {
            using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
            {
                // Write all data to the stream
                swEncrypt.Write(str2Encrypt);
            }

            encryptedText = msEncrypt.ToArray();
        }
    }

    return Encoding.Default.GetString(encryptedText);
}

I use Encoding.Default to convert a byte array to a string but I'm not sure it's a good solution. My goal is to store encrypted text (such as passwords...) in files. Should I continue with Encoding.Default or use Encoding.UTF8Encoding or something else?

Can that have negative consequences on the stored values when I try to encrypt and decrypt them if the files are moved onto different OS'?

Answer 1

You should absolutely not use an Encoding to convert arbitrary binary data to text. Encoding is for when you've got binary data which genuinely is encoded text - this isn't.

Instead, use Convert.ToBase64String to encode the binary data as text, then decode using Convert.FromBase64String .

Answer 2

If your goal is to store encrypted information in files, and you have a byte array, you should store it directly - don't convert it to a string at all. For example, in C# you can use File.WriteAllBytes to write a byte array directly to a file. Remember that files hold bytes, not strings (if you write a string into a file, some kind of Encoding will be used to convert it to bytes, even if you are using a technique that doesn't explicitly refer to Encoding ).

If you actually need the byte array to be stored as a string (for example, because it will be stored in JSON) then the most common technique is to use base64 with Convert.ToBase64String , as Jon mentioned.

(In non-encryption applications you might have a byte[] that contains a mixture of ASCII and binary data and you want to convert it to a string. In this case base64 works fine but it hides the text - Byte Array In String format is like base64 except that runs of ASCII are preserved - C# version in Loyc.Essentials NuGet package, Java version here )

Answer 3

Yes, Encoding.Default is your machine's current ANSI code page and may well be different between multiple machines/locales. If the data was textual data and to make it portable, you would need to use a fixed encoding format, for example UTF8.

However, as your data is NOT textual data, you can not try and use any textual encoding to convert to a string. The best option is to use a hex or Base64 encoding or keep it as a blob/byte array.

Answer 4

im not 100% sure here but i think that Encoding.Default refers to the system default encoding and yes that can change from system to system..

If i where you i would use UTF8 or some other encoding that does not change from system to system..

for more info about extended ascii look here

http://en.wikipedia.org/wiki/Extended_ASCII