public static string DecryptEncryptedFile(EncryptedFileParameters @params)
{
//========================================================================
// Decrypt encrypted symmetric key with private key.
var rsa = EncryptController.ImportPrivateKey(Directory.GetCurrentDirectory() +
$"/../../CurrentUsers/{AccountsController.GetInstance().CurrentAccount.Username}.key");
var symmetricKey =
Encoding.Unicode.GetString(rsa.Decrypt(Convert.FromBase64String(@params.EncryptedSymmetricKey), false));
//========================================================================
// Decrypt encrypted sendername.
var decryptedName = Cipher.Decrypt(@params.EncryptedSenderName, symmetricKey, @params.SymmetricAlgorithm);
//========================================================================
// Validate sender and receiver certificate.
var senderAccount = AccountsController.GetInstance().Accounts[decryptedName];
var senderCertificate = new X509Certificate2();
senderCertificate.Import(senderAccount.PathToCertificate);
var receiverAccount = AccountsController.GetInstance().CurrentAccount;
var receiverCertificate = new X509Certificate2();
receiverCertificate.Import(receiverAccount.PathToCertificate);
if (!ValidateController.ValidateCertificates(receiverCertificate))
{
return("");
}
if (!ValidateController.ValidateCertificates(senderCertificate))
{
return("");
}
//========================================================================
// Decrypt digital signature with symmetric key.
var digitalSignature = Convert.FromBase64String(
Cipher.Decrypt(@params.EncryptedSignature, symmetricKey, @params.SymmetricAlgorithm));
//========================================================================
// Decrypt data with symmetric key.
var decryptedData = Cipher.Decrypt(@params.EncryptedData, symmetricKey, @params.SymmetricAlgorithm);
//========================================================================
// Verify messagehash with signature.
var decryptedHashAlg = Cipher.Decrypt(@params.EncryptedHashAlg, symmetricKey, @params.SymmetricAlgorithm);
var rsaCrypto = (RSACryptoServiceProvider)senderCertificate.PublicKey.Key;
if (!VerifyData(Encoding.Unicode.GetBytes(decryptedData), digitalSignature, rsaCrypto.ExportParameters(false), decryptedHashAlg))
{
return(null);
}
//========================================================================
// Return a message.
return(decryptedData);
}
public static Account ReadSessionRequest(Account receiver, bool isResponse, object locker)
{
var file = Directory.GetFiles(Directory.GetCurrentDirectory() + @"\..\..\ChatRequests", isResponse ? "*.sesres" : "*.sesreq")
.FirstOrDefault(e => Path.GetFileNameWithoutExtension(e) == receiver.Username);
if (file == null)
{
return(null);
}
string content;
lock (locker)
{
while (true)
{
try
{
content = Steganography.ExtractText(
new Bitmap(Image.FromFile(file))
);
break;
}
catch (Exception)
{
Task.Delay(1000);
}
}
}
//========================================================================
// Decrypt encrypted sender username with private key.
var rsa = EncryptController.ImportPrivateKey(Directory.GetCurrentDirectory() +
$@"\..\..\CurrentUsers\{AccountsController.GetInstance().CurrentAccount.Username}.key");
var senderUsername =
Encoding.Unicode.GetString(rsa.Decrypt(Convert.FromBase64String(content), false));
//========================================================================
// Validate sender and receiver certificate.
var senderAccount = AccountsController.GetInstance().CurrentAccount;
var senderCertificate = new X509Certificate2();
senderCertificate.Import(senderAccount.PathToCertificate);
var receiverCertificate = new X509Certificate2();
receiverCertificate.Import(receiver.PathToCertificate);
if (!ValidateController.ValidateCertificates(receiverCertificate))
{
return(null);
}
if (!ValidateController.ValidateCertificates(senderCertificate))
{
return(null);
}
return(AccountsController.GetInstance().Accounts[senderUsername]);
}
public static bool CreateSessionRequestResponse(Account sender, Account receiver, bool isResponse, object locker)
{
//========================================================================
// Validate sender and receiver certificate.
var senderAccount = AccountsController.GetInstance().CurrentAccount;
var senderCertificate = new X509Certificate2();
senderCertificate.Import(senderAccount.PathToCertificate);
var receiverCertificate = new X509Certificate2();
receiverCertificate.Import(receiver.PathToCertificate);
if (!ValidateController.ValidateCertificates(receiverCertificate))
{
return(false);
}
if (!ValidateController.ValidateCertificates(senderCertificate))
{
return(false);
}
//========================================================================
// Encrypt sender username with receiver public key and save it into textfile.
// Receiver can only read it, only he has his private key.
var rsaprovider = (RSACryptoServiceProvider)receiverCertificate.PublicKey.Key;
var encryptedSenderName =
Convert.ToBase64String(rsaprovider.Encrypt(Encoding.Unicode.GetBytes(senderAccount.Username), false));
string path = Directory.GetCurrentDirectory() +
$@"\..\..\ChatRequests\{receiver.Username}.{(isResponse ? "sesres" : "sesreq")}";
lock (locker)
{
while (true)
{
try
{
var stegBitmap = Steganography.MergeText(encryptedSenderName, bitmap);
stegBitmap.Save(path);
break;
}
catch (Exception)
{
Task.Delay(1000);
}
}
}
return(true);
}
public Account GetAccount(string username, string password, string pathToCertificate)
{
var acc = Accounts.TryGetValue(username, out var tmp) ? tmp : null;
if (acc == null)
{
return(null);
}
var data = Encoding.Unicode.GetBytes(password);
HashAlgorithm ha = new MD5CryptoServiceProvider();
var hashpass = Encoding.Unicode.GetString(ha.ComputeHash(data));
var cert = new X509Certificate2();
cert.Import(pathToCertificate);
if (!ValidateController.ValidateCertificates(cert))
{
return(null);
}
return(File.Exists(pathToCertificate) &&
username == Program.ReadName(cert) &&
acc.PasswordHash == hashpass
? acc
: null);
}
public static string DecryptEncryptedFile(EncryptedFileParameters @params)
{
//========================================================================
// Decrypt encrypted symmetric key with private key.
var rsa = EncryptController.ImportPrivateKey(Directory.GetCurrentDirectory() +
"/../../CurrentUser/private.key");
var symmetricKey =
Encoding.Unicode.GetString(rsa.Decrypt(Convert.FromBase64String(@params.EncryptedSymmetricKey), false));
//========================================================================
// Decrypt encrypted sender and filename.
var decryptedName = Cipher.Decrypt(@params.EncryptedName, symmetricKey, @params.SymmetricAlgorithm);
//========================================================================
// Validate sender and receiver certificate.
var senderAccount = AccountsController.GetInstance().Accounts[decryptedName];
var senderCertificate = new X509Certificate2();
senderCertificate.Import(senderAccount.PathToCertificate);
var receiverAccount = AccountsController.GetInstance().CurrentAccount;
var receiverCertificate = new X509Certificate2();
receiverCertificate.Import(receiverAccount.PathToCertificate);
if (!ValidateController.ValidateCertificates(receiverCertificate))
{
return("");
}
if (!ValidateController.ValidateCertificates(senderCertificate))
{
return("");
}
//========================================================================
// Decrypt digital signature with symmetric key.
var digitalSignature = Convert.FromBase64String(
Cipher.Decrypt(@params.EncryptedSignature, symmetricKey, @params.SymmetricAlgorithm));
//========================================================================
// Decrypt file with symmetric key.
var decryptedFileName = Cipher.Decrypt(@params.EncryptedFileName, symmetricKey, @params.SymmetricAlgorithm);
var decryptedFile = Encoding.Unicode.GetBytes(
Cipher.Decrypt(@params.EncryptedData, symmetricKey, @params.SymmetricAlgorithm));
//========================================================================
// Verify filehash with signature.
var decryptedHashAlg = Cipher.Decrypt(@params.EncryptedHashAlg, symmetricKey, @params.SymmetricAlgorithm);
var rsaCrypto = (RSACryptoServiceProvider)senderCertificate.PublicKey.Key;
if (!VerifyData(decryptedFile, digitalSignature, rsaCrypto.ExportParameters(false), decryptedHashAlg))
{
MessageBox.Show("File is changed! Unsuccessfully decrypt. 😐");
return("");
}
//========================================================================
// Write file on filesystem.
var parentPath = Directory.GetCurrentDirectory() + "/../../DecryptedMessages";
var currentUsername = AccountsController.GetInstance().CurrentAccount.Username;
var path = $"{parentPath}/{currentUsername}/{decryptedName}/{Path.GetFileName(decryptedFileName)}";
if (!Directory.Exists($"{parentPath}/{currentUsername}/{decryptedName}/"))
{
Directory.CreateDirectory($"{parentPath}/{currentUsername}/{decryptedName}/");
}
File.WriteAllBytes(path, decryptedFile);
return(path);
}