public static byte[] GetAdditionalData(string inputFilePath)
{
byte[] magicBytes = FileHeaders.ReadMagicBytes(inputFilePath);
byte[] formatVersion = FileHeaders.ReadFileFormatVersion(inputFilePath);
FileHeaders.ValidateFormatVersion(inputFilePath, formatVersion, Constants.EncryptionVersion);
long fileLength = FileHandling.GetFileLength(inputFilePath);
int headersLength = FileHeaders.GetHeadersLength();
byte[] ciphertextLength = BitConverter.GetBytes(fileLength - headersLength);
return(Utilities.ConcatArrays(magicBytes, formatVersion, ciphertextLength));
}
private static void Decrypt(FileStream inputFile, FileStream outputFile, byte[] nonce, byte[] dataEncryptionKey, byte[] additionalData, int lastChunkLength)
{
int headersLength = FileHeaders.GetHeadersLength();
inputFile.Seek(headersLength, SeekOrigin.Begin);
const int offset = 0;
byte[] ciphertextChunk = new byte[Constants.TotalChunkLength];
while (inputFile.Read(ciphertextChunk, offset, ciphertextChunk.Length) > 0)
{
byte[] plaintextChunk = SecretAeadXChaCha20Poly1305.Decrypt(ciphertextChunk, nonce, dataEncryptionKey, additionalData);
ChunkHandling.ValidateKeyCommitmentBlock(plaintextChunk);
nonce = Sodium.Utilities.Increment(nonce);
additionalData = ChunkHandling.GetPreviousPoly1305Tag(ciphertextChunk);
plaintextChunk = ChunkHandling.RemoveKeyCommitmentBlock(plaintextChunk);
outputFile.Write(plaintextChunk, offset, plaintextChunk.Length);
}
outputFile.SetLength((outputFile.Length - Constants.FileChunkSize) + lastChunkLength);
Utilities.ZeroArray(dataEncryptionKey);
}