/// <summary>
/// - Gets specific encrypted source file from server.
/// - Encryption and Decription using AES symetric and commonSecret derived from EC Diffie-Helman key Exchange
/// - Decrypts source files
/// - verifies digital signature of source code
/// </summary>
/// <param name="sourceFileInfo">the file to get</param>
/// <returns>verified and decrypted source file or null if operation unsuccessfull</returns>
private string DecryptSourceFromServer(SourceFileInfo sourceFileInfo)
{
byte[] dhClientPublic;
byte[] dhClientPrivate;
_keyGen.GenerateKeyPair(out dhClientPrivate, out dhClientPublic);
string uri = (TroubleShooterClient.SERVICE_PATH + "/source");
ProtectedSourceRequest request = new ProtectedSourceRequest()
{
DhClientPublic = dhClientPublic, FileName = sourceFileInfo.FileName
};
HttpResponseMessage response = _client.PostAsJsonAsync(uri, request).GetAwaiter().GetResult();
if (response.IsSuccessStatusCode)
{
ProtectedSource source = response.Content.ReadAsAsync <ProtectedSource>().GetAwaiter().GetResult();
byte[] sharedSecret = _diffieHelman.SharedSecret(dhClientPrivate, source.DhPublicServer);
string decryptedSource = AesHandler.DecryptStringFromBytes_Aes(source.SourceCode, sharedSecret);
if (_verifier.VerifySignature(decryptedSource, source.Signature, _signatureKey))
{
return(decryptedSource);
}
else
{
return(null);
}
}
return(null);
}
public ProtectedSource Get([FromBody] ProtectedSourceRequest request)
{
//read source code
string sourceCode = System.IO.File.ReadAllText(Path.Combine(SOURCE_FILES_DIR, request.FileName));
//generate key pair and derive shared secret
byte[] dhServerPublic;
byte[] dhServerPrivate;
keyGen.GenerateKeyPair(out dhServerPrivate, out dhServerPublic);
byte[] sharedSecret = diffieHelman.SharedSecret(dhServerPrivate, request.DhClientPublic);
//send encrypted and signed source back to client;
//send also servers public key so client can derive common secret
return(new ProtectedSource()
{
SourceCode = AesHandler.EncryptStringToBytes_Aes(sourceCode, sharedSecret),
DhPublicServer = dhServerPublic,
Signature = signatureMaker.Signature(sourceCode, signatureKey)
});
}
