private static byte[] Decrypt(NppCryptCipherParams cipher, byte[] encryptedData, string password)
{
if (cipher.Encryption.Cipher != "rijndael")
{
throw new Exception($"Cipher algorithm \"{cipher.Encryption.Cipher}\" is not supported now. " +
"Only \"rijndael\" algorithm might be used in the current version");
}
if (cipher.Encryption.Mode != CipherMode.CBC)
{
throw new Exception($"Cipher algorithm mode \"{cipher.Encryption.Mode}\" is not supported now. " +
$"Only \"{nameof(CipherMode.CBC)}\" mode might be used in the current version");
}
if (cipher.Key.Algorithm != "scrypt")
{
throw new Exception($"Key hashing algorithm \"{cipher.Key.Algorithm}\" is not supported now. " +
"Only \"scrypt\" algorithm might be used in the current version");
}
if (!cipher.Key.N.HasValue)
{
throw new Exception($"Parameter '{nameof(cipher.Key.N)}' of key hashing algorithm is not set");
}
if (!cipher.Key.R.HasValue)
{
throw new Exception($"Parameter '{nameof(cipher.Key.R)}' of key hashing algorithm is not set");
}
if (!cipher.Key.P.HasValue)
{
throw new Exception($"Parameter '{nameof(cipher.Key.P)}' of key hashing algorithm is not set");
}
if (cipher.Key.Salt == null)
{
throw new Exception($"Parameter '{nameof(cipher.Key.Salt)}' of key hashing algorithm is not set");
}
var key = ScryptEncoder.CryptoScrypt(Encoding.UTF8.GetBytes(password), cipher.Key.Salt,
cipher.Key.N.Value, cipher.Key.R.Value, cipher.Key.P.Value, cipher.Encryption.KeyLength ?? 32);
using Rijndael rijAlg = Rijndael.Create();
rijAlg.Key = key;
rijAlg.IV = cipher.Iv.Value;
rijAlg.Mode = cipher.Encryption.Mode;
using var ms = new MemoryStream();
using var cs = new CryptoStream(ms, rijAlg.CreateDecryptor(), CryptoStreamMode.Write);
cs.Write(encryptedData, 0, encryptedData.Length);
cs.Close();
var res = ms.ToArray();
ms.Close();
return(res);
}
private static NppCryptCipherParams ParseCipherParams(string nppCryptXml)
{
XmlDocument doc;
try
{
doc = new XmlDocument();
doc.LoadXml(nppCryptXml);
}
catch (Exception e)
{
throw new Exception("NppCrypt-header parsing exception", e);
}
var res = new NppCryptCipherParams
{
Encryption = new NppCryptEncryptionParams(),
Key = new NppCryptKeyParams(),
Iv = new NppCryptIvParams()
};
XmlNode getTag(XmlNode parent, string tagName)
{
using (var tagCollection = (parent as XmlElement)?.GetElementsByTagName(tagName))
{
if (tagCollection?.Count != 1)
{
throw new Exception($"NppCrypt-header parsing exception. The \"<{tagName}>\" tag was not found " +
"or is present in several instances");
}
return(tagCollection[0]);
}
}
string getAttribute(XmlNode parent, string attributeName)
{
return(parent?.Attributes?[attributeName]?.Value);
}
byte[] parseBase64String(string str)
{
try
{
return(Convert.FromBase64String(str));
}
catch
{
return(null);
}
}
CipherMode parseMode(string mode)
{
var m = mode.Trim().ToUpperInvariant();
var modes = Enum.GetValues(typeof(CipherMode)).Cast <CipherMode>().ToList();
foreach (var cipherMode in modes)
{
if (cipherMode.ToString().ToUpperInvariant() == m)
{
return(cipherMode);
}
}
throw new Exception($"Unknown cipher mode '{mode}'");
}
var encryptionTag = getTag(doc.DocumentElement, "encryption");
res.Encryption.Cipher = getAttribute(encryptionTag, "cipher");
if (int.TryParse(getAttribute(encryptionTag, "key-length"), out int keyLen))
{
res.Encryption.KeyLength = keyLen;
}
res.Encryption.Mode = parseMode(getAttribute(encryptionTag, "mode"));
res.Encryption.Encoding = getAttribute(encryptionTag, "encoding");
var keyTag = getTag(doc.DocumentElement, "key");
res.Key.Algorithm = getAttribute(keyTag, "algorithm");
if (int.TryParse(getAttribute(keyTag, "N"), out int n))
{
res.Key.N = n;
}
if (int.TryParse(getAttribute(keyTag, "r"), out int r))
{
res.Key.R = r;
}
if (int.TryParse(getAttribute(keyTag, "p"), out int p))
{
res.Key.P = p;
}
res.Key.Salt = parseBase64String(getAttribute(keyTag, "salt"));
var ivTag = getTag(doc.DocumentElement, "iv");
res.Iv.Value = parseBase64String(getAttribute(ivTag, "value"));
res.Iv.Method = getAttribute(ivTag, "method");
return(res);
}
