How to convert AES byte[] into string and vice versa?

Question

My method AESEncrypt(string text) is returning a byte array. If I encrypt a message, and use the returned byte array as an input for AESDecrypt(byte[] text), everything is working fine. The problem is, that I need to convert it to a string and vice versa, so I tried the following:

byte[] encrypted = enc.AESEncrypt("Testmessage");
string encryptedStr = Convert.ToBase64String(encrypted);
byte[] test = Convert.FromBase64String(encryptedStr);

Console.WriteLine((encrypted == test));

I also tried this with Encoding.ASCII.GetString(), Encoding.UTF8.GetString(),

but encrypted == test returns false everytime...

What method do I need to use to convert the AES byte[] to a string and vice versa?

This is the AESEncrypt method:

public byte[] AESEncrypt(string s)
{
    byte[] encrypted;

    using (AesManaged aes = new AesManaged()) {
        ICryptoTransform encryptor = aes.CreateEncryptor(AESKey, AESIV);
        using (MemoryStream ms = new MemoryStream()) {
            using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write)) {
                using (StreamWriter sw = new StreamWriter(cs)) {
                    sw.Write(s);
                }
                encrypted = ms.ToArray();
            }
        }
    }

    return encrypted;
}

What kind of string? Base64? Hex? I recommend reading [this](https://haacked.com/archive/2012/01/30/hazards-of-converting-binary-data-to-a-string.aspx/) if you want to know why text encoding methods didn't work. In short: they're not built for it. — ProgrammingLlama, Nov 28 '18 at 08:58

score 4 · Accepted Answer · answered Nov 28 '18 at 09:12

An encrypted payload held in a byte array is not directly convertible to a string, or at least not without using an ANSI encoding and both sides (encoding and decoding) agreeing on the string's code page. And if you use any Unicode encoding (UTF-8, UTF-16, ...) you're bound to have bytes that contain invalid code points, so who can't be decoded to a character.

That's where base64 comes into play. This is a safe way to represent byte arrays as ASCII strings, a subset implemented by almost every (if not every) encoding. So using that base64 code is fine.

You'll simply want encrypted.SequenceEquals(test), as explained in Comparing two byte arrays in .NET.

Thank you very much for the answer. My equality check was simply wrong. encrypted.SequenceEqual(test) is returning true. — Nico Schreiner, Nov 28 '18 at 09:16
Perfectly explained, and just the answer I was looking for. Thanks! — Yash Gupta, Oct 06 '21 at 12:32

score 1 · Answer 2 · answered Nov 28 '18 at 10:55

The base64 is directly used for this. here is an example:

Encode

public static string Base64Encode(string plainText)
{
    var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
    return System.Convert.ToBase64String(plainTextBytes);
}

Decode

public static string Base64Decode(string base64EncodedData)
{
    var base64EncodedBytes = System.Convert.FromBase64String(base64EncodedData);
    return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
}

score 0 · Answer 3 · answered Nov 28 '18 at 09:01

Consider byte[] encrypted and byte[] test, when you test for equality with == by default the references are compared not their content. This explains, why you test encrypted == test fails.

You are also asking about how to convert byte[] into a string, which is not related to your encrypted == test test at all. In general you the various System.Text.Encoding.*.GetString(byteArray); preform the conversion but you need to know what encoding was used for the byteArray. This information has to be passed along separately, you might have a specification which says all byte arrays are encoded in UTF-8 or you might pass the encoding along together with the data but there exists no general answer.

My point is that I want to know if there is a method which allows me to convert a byte array to a string and the string back to the byte array without losing any data. That is the reason why I compare the two arrays. — Nico Schreiner, Nov 28 '18 at 09:07

How to convert AES byte[] into string and vice versa?

3 Answers3