private EncryptedFile.Footer ReadOrWriteFooter()
{
lock (locker)
{
if (stream.Length >= EncryptedFile.Header.HeaderSize + EncryptedFile.Footer.FooterSize)
{
// Read footer
stream.Position = stream.Length - EncryptedFile.Footer.FooterSize;
var footerBytes = stream.ReadEntireBlock(EncryptedFile.Footer.FooterSize);
var footer = StructConverter.ConvertBitsToStruct <EncryptedFile.Footer>(footerBytes);
// Sanity check that the footer has some value that could be correct
var streamBlockLength = (stream.Length - (EncryptedFile.Header.HeaderSize + EncryptedFile.Footer.FooterSize)) / header.DiskBlockSize;
var footerBlockLength = footer.TotalLength / header.DecryptedBlockSize;
if (footerBlockLength != streamBlockLength - 1 && footerBlockLength != streamBlockLength)
{
throw new InvalidDataException("File is corrupted: the length written to the file doesn't match the number of blocks in it.");
}
return(footer);
}
else
{
// Write footer
stream.Position = EncryptedFile.Header.HeaderSize;
var footer = new EncryptedFile.Footer {
TotalLength = 0
};
WriteFooterInCurrentPosition(footer);
return(footer);
}
}
}
private EncryptedFile.Header ReadOrWriteEmptyHeader(int defaultBlockSize)
{
lock (locker)
{
stream.Position = 0;
if (stream.Length >= EncryptedFile.Header.HeaderSize)
{
// Read header
int headerSize;
var magicNumber = stream.ReadUInt64();
switch (magicNumber)
{
case EncryptedFile.DefaultMagicNumber: //old header struct --> without the last field
headerSize = EncryptedFile.Header.HeaderSize - Marshal.SizeOf(typeof(long));
break;
case EncryptedFile.WithTotalSizeMagicNumber:
headerSize = EncryptedFile.Header.HeaderSize;
break;
default:
throw new ApplicationException("Invalid magic number");
}
stream.Position = 0;
var headerBytes = stream.ReadEntireBlock(headerSize);
var fileHeader = StructConverter.ConvertBitsToStruct <EncryptedFile.Header>(headerBytes);
if (fileHeader.MagicNumber != EncryptedFile.DefaultMagicNumber && fileHeader.MagicNumber != EncryptedFile.WithTotalSizeMagicNumber)
{
throw new InvalidDataException("The magic number in the file doesn't match the expected magic number for encrypted files. Perhaps this file isn't encrypted?");
}
return(fileHeader);
}
else
{
// Write empty header
var sizeTest = settings.Codec.EncodeBlock("Dummy key", new byte[defaultBlockSize]);
var fileHeader = new EncryptedFile.Header
{
MagicNumber = EncryptedFile.WithTotalSizeMagicNumber,
DecryptedBlockSize = defaultBlockSize,
IVSize = sizeTest.IV.Length,
EncryptedBlockSize = sizeTest.Data.Length,
TotalUnencryptedSize = EncryptedFile.Header.HeaderSize + EncryptedFile.Footer.FooterSize
};
WriteHeaderInCurrentPositionIfNotReadonly(fileHeader);
return(fileHeader);
}
}
}
private EncryptedFile.Header ReadOrWriteHeader(int defaultBlockSize)
{
lock (locker)
{
stream.Position = 0;
if (stream.Length >= EncryptedFile.Header.HeaderSize)
{
// Read header
var headerBytes = stream.ReadEntireBlock(EncryptedFile.Header.HeaderSize);
var header = StructConverter.ConvertBitsToStruct <EncryptedFile.Header>(headerBytes);
if (header.MagicNumber != EncryptedFile.DefaultMagicNumber)
{
throw new InvalidDataException("The magic number in the file doesn't match the expected magic number for encypted files. Perhaps this file isn't encrypted?");
}
return(header);
}
else
{
// Write header
var sizeTest = settings.Codec.EncodeBlock("Dummy key", new byte[defaultBlockSize]);
var header = new EncryptedFile.Header
{
MagicNumber = EncryptedFile.DefaultMagicNumber,
DecryptedBlockSize = defaultBlockSize,
IVSize = sizeTest.IV.Length,
EncryptedBlockSize = sizeTest.Data.Length
};
var headerBytes = StructConverter.ConvertStructToBits(header);
if (!isReadonly)
{
stream.Write(headerBytes, 0, EncryptedFile.Header.HeaderSize);
}
return(header);
}
}
}
private EncryptedFile.Header ReadOrWriteEmptyHeader(int defaultBlockSize)
{
lock (locker)
{
stream.Position = 0;
if (stream.Length >= EncryptedFile.Header.HeaderSize)
{
// Read header
var magicNumber = stream.ReadUInt64();
var headerSize = GetHeaderSizeByMagicNumber(magicNumber);
stream.Position = 0;
var headerBytes = stream.ReadEntireBlock(headerSize);
var fileHeader = StructConverter.ConvertBitsToStruct <EncryptedFile.Header>(headerBytes, headerSize);
if (fileHeader.MagicNumber != EncryptedFile.DefaultMagicNumber && fileHeader.MagicNumber != EncryptedFile.WithTotalSizeMagicNumber)
{
throw new InvalidDataException("The magic number in the file doesn't match the expected magic number for encrypted files. Perhaps this file isn't encrypted?");
}
return(fileHeader);
}
else
{
// Write empty header
var sizeTest = settings.Codec.EncodeBlock("Dummy key", new byte[defaultBlockSize]);
var fileHeader = new EncryptedFile.Header
{
MagicNumber = EncryptedFile.WithTotalSizeMagicNumber,
DecryptedBlockSize = defaultBlockSize,
IVSize = sizeTest.IV.Length,
EncryptedBlockSize = sizeTest.Data.Length,
TotalUnencryptedSize = 0
};
WriteHeaderInCurrentPositionIfNotReadonly(fileHeader, fileHeader.MagicNumber);
return(fileHeader);
}
}
}
