/// <summary>
/// Encrypts and MACs some plaintext with a passphrase
/// </summary>
/// <param name="passphrase">Password to encrypt/MAC</param>
/// <param name="plaintext">Text to protect</param>
/// <returns>Base64 ciphertext blob</returns>
public string EncryptAndMac(string passphrase, string plaintext)
{
if (passphrase.Length == 0 || plaintext.Length == 0)
{
throw new ArgumentException();
}
// generate a salt from random data (24 bytes) + system tick count (8 bytes)
byte[] ticks = BitConverter.GetBytes(DateTime.Now.Ticks);
var tempSalt = new byte[_salt.Length - ticks.Length];
new RNGCryptoServiceProvider().GetBytes(tempSalt);
Array.Copy(tempSalt, _salt, tempSalt.Length);
Array.Copy(ticks, 0, _salt, tempSalt.Length, ticks.Length);
// get PBKDF info and create object (salt is ignored from config file)
string s = _configData[LinePbkdfsettings].Split(Delim)[1];
dynamic dp = new JavaScriptSerializer().DeserializeObject(s);
int iter = int.Parse(dp["IterationCount"].ToString());
_pbkdf = new Rfc2898DeriveBytes(passphrase, _salt, iter);
// get symmetric cipher info and create object
_sym = SymmetricAlgorithm.Create(_configData[LineSymalgsettings].Split(Delim)[0]);
dynamic ds = new JavaScriptSerializer().
DeserializeObject(_configData[LineSymalgsettings].Split(Delim)[1]);
_sym.BlockSize = ds["BlockSize"];
_sym.KeySize = ds["KeySize"];
_sym.Mode = (CipherMode)ds["Mode"];
_sym.Padding = (PaddingMode)ds["Padding"];
// get HMAC settings and create object
// TODO: currently uses default alg (SHA-256), need to make it configurable, too
_hmac = HMAC.Create(_configData[LineHmacsettings].Split(Delim)[0]);
//
// Do the dirty work
//
// generate symmetric key and HMAC key
_sym.Key = _pbkdf.GetBytes(_sym.KeySize >> 3);
_hmac.Key = _pbkdf.GetBytes(_hmac.HashSize >> 3);
// perform the crypto opertions
string ciphertext = Encrypt(plaintext);
// encrypt then MAC - this MACs the ciphertext
string hmac = CalculateHmac(ciphertext);
// serialize the symmetric alg, but strip out the key
var oSerializer = new JavaScriptSerializer();
// clear all keys
//_sym.Key = new byte[_sym.Key.Length];
//_hmac.Key = new byte[_hmac.Key.Length];
// serialize the ciphertext/HMAC/PKBDF
string sJsonSym = RemoveJunkFromJson(oSerializer.Serialize(_sym));
string sJsonHmac = RemoveJunkFromJson(oSerializer.Serialize(_hmac));
string sJsonPbkdf = oSerializer.Serialize(_pbkdf);
// build the resulting cipherblob string
var sb = new StringBuilder();
sb.Append(_pbkdf.ToString() + Delim + sJsonPbkdf + Crlf);
sb.Append(_sym.ToString() + Delim + sJsonSym + Crlf);
sb.Append(_hmac.ToString() + Delim + sJsonHmac + Crlf);
sb.Append(ciphertext + Crlf);
sb.Append(hmac);
return(sb.ToString());
}