public static byte[] ComputeAdditionalData(long fileLength, byte[] ephemeralPublicKey)
{
long chunkCount = (long)Math.Ceiling((double)fileLength / Constants.FileChunkSize);
byte[] ciphertextLength = BitConversion.GetBytes(chunkCount * Constants.TotalChunkLength);
return(Arrays.Concat(ciphertextLength, Constants.KryptorMagicBytes, Constants.EncryptionVersion, ephemeralPublicKey));
}
public static byte[] GetAdditionalData(FileStream inputFile, byte[] ephemeralPublicKey)
{
byte[] ciphertextLength = BitConversion.GetBytes(inputFile.Length - Constants.FileHeadersLength);
byte[] magicBytes = FileHeaders.ReadMagicBytes(inputFile);
byte[] formatVersion = FileHeaders.ReadFileFormatVersion(inputFile);
FileHeaders.ValidateFormatVersion(formatVersion, Constants.EncryptionVersion);
return(Arrays.Concat(ciphertextLength, magicBytes, formatVersion, ephemeralPublicKey));
}
private static byte[] EncryptFileHeader(string inputFilePath, byte[] ephemeralPublicKey, byte[] dataEncryptionKey, byte[] nonce, byte[] keyEncryptionKey)
{
long fileLength = FileHandling.GetFileLength(inputFilePath);
byte[] lastChunkLength = BitConversion.GetBytes(Convert.ToInt32(fileLength % Constants.FileChunkSize));
byte[] fileNameLength = FileHeaders.GetFileNameLength(inputFilePath);
byte[] fileHeader = Arrays.Concat(lastChunkLength, fileNameLength, dataEncryptionKey);
byte[] additionalData = HeaderEncryption.ComputeAdditionalData(fileLength, ephemeralPublicKey);
return(HeaderEncryption.Encrypt(fileHeader, nonce, keyEncryptionKey, additionalData));
}
public static byte[] GetFileNameLength(string inputFilePath)
{
if (!Globals.ObfuscateFileNames)
{
return(BitConversion.GetBytes(0));
}
string fileName = Path.GetFileName(inputFilePath);
byte[] fileNameBytes = Encoding.UTF8.GetBytes(fileName);
return(BitConversion.GetBytes(fileNameBytes.Length));
}