Is it possible to get colon in encrypted string using Base64

Question

I'm using below method to encrypt a password which I later on save in a string that I separate with a colon like this:

username:MyEncryptedString

My question is, is it possible that my method could return a string containing a colon?

public static string EncryptString(string password, string sharedSecret) {
    if (string.IsNullOrEmpty(password))
        throw new ArgumentNullException("password");
    if (string.IsNullOrEmpty(sharedSecret))
        throw new ArgumentNullException("sharedSecret");

    string outStr = null;                       // Encrypted string to return
    RijndaelManaged aesAlg = null;              // RijndaelManaged object used to encrypt the data.

    try {
        // generate the key from the shared secret and the salt
        Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, Salt);

        // Create a RijndaelManaged object
        aesAlg = new RijndaelManaged();
        aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);

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

        // Create the streams used for encryption.
        using (MemoryStream msEncrypt = new MemoryStream()) {
            // prepend the IV
            msEncrypt.Write(BitConverter.GetBytes(aesAlg.IV.Length), 0, sizeof(int));
            msEncrypt.Write(aesAlg.IV, 0, aesAlg.IV.Length);
            using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)) {
                using (StreamWriter swEncrypt = new StreamWriter(csEncrypt)) {
                    //Write all data to the stream.
                    swEncrypt.Write(password);
                }
            }
            outStr = Convert.ToBase64String(msEncrypt.ToArray());
        }
    } finally {
        // Clear the RijndaelManaged object.
        if (aesAlg != null)
            aesAlg.Clear();
    }

    // Return the encrypted bytes from the memory stream.
    return outStr;
}

Answer 1

Modern ciphers produce binary output that should be indistinguishable from random noise. If you interpret this binary output as text (ASCII, UTF-8, etc.) you might see a : in there if the ciphertext is long enough. But you also see it for shorter ciphertexts, but not necessarily in every one. The point is, the output is binary and not a "string".

It is possible to encode the binary output to get a string. If Base 64 or Hex are used, then there is no way to get a : , because that's not in their alphabet. If you decide to use Base 85 encoding, then you might get a : , depending on the specific alphabet (eg Z85 ).