/// <summary>
/// (Crudely) determines if file is a CourseSmart file
/// </summary>
/// <param name="file">Path to file to check</param>
/// <returns>True if successful; null otherwise</returns>
public static bool IsCourseSmartFile(string file)
{
CourseSmartReader reader = new CourseSmartReader(file);
byte firstByte = reader.ReadByte();
if (firstByte == 0 || firstByte > 5)
{
// first byte in file must be 1-5
return(false);
}
switch (firstByte)
{
case 1:
// no restrictions, no key/value pairs, just file data
break;
case 2:
// check for width/height/offset
uint width = reader.ReadUInt16();
uint height = reader.ReadUInt16();
uint offset = reader.ReadUInt16();
if (width == 0 || height == 0 || offset == 0)
{
// should have some value here
return(false);
}
break;
case 3:
uint numberOfKeyValuePairs = reader.ReadUInt16();
if (numberOfKeyValuePairs == 0 || numberOfKeyValuePairs > 20)
{
// sanity check on how many key value pairs we will read
// should be more than 0 as we need a book name & page #,
// but there shouldnt be more than 10ish (most I've seen
// is 8, but lets call it 20)
return(false);
}
break;
case 4:
case 5:
// both of these are error cases, no sense loading them as
// there shouldnt be anything here
return(false);
}
return(true);
}
/// <summary>
/// (Crudely) determines if file is a CourseSmart file
/// </summary>
/// <param name="file">Path to file to check</param>
/// <returns>True if successful; null otherwise</returns>
public static bool IsCourseSmartFile(string file)
{
CourseSmartReader reader = new CourseSmartReader(file);
byte firstByte = reader.ReadByte();
if (firstByte == 0 || firstByte > 5)
{
// first byte in file must be 1-5
return false;
}
switch (firstByte)
{
case 1:
// no restrictions, no key/value pairs, just file data
break;
case 2:
// check for width/height/offset
uint width = reader.ReadUInt16();
uint height = reader.ReadUInt16();
uint offset = reader.ReadUInt16();
if (width == 0 || height == 0 || offset == 0)
{
// should have some value here
return false;
}
break;
case 3:
uint numberOfKeyValuePairs = reader.ReadUInt16();
if (numberOfKeyValuePairs == 0 || numberOfKeyValuePairs > 20)
{
// sanity check on how many key value pairs we will read
// should be more than 0 as we need a book name & page #,
// but there shouldnt be more than 10ish (most I've seen
// is 8, but lets call it 20)
return false;
}
break;
case 4:
case 5:
// both of these are error cases, no sense loading them as
// there shouldnt be anything here
return false;
}
return true;
}
/// <summary>
/// Decryption routine - extracted from offline viewer code
/// </summary>
/// <param name="data">Byte List containing encrypted movie data</param>
private void DecryptMovieData(ref byte[] data)
{
// load encrypted data into cs reader
using (MemoryStream dataStream = new MemoryStream(data))
using (CourseSmartReader dataReader = new CourseSmartReader(dataStream))
{
byte XORKeyLength = dataReader.ReadByte();
byte SPECIAL = dataReader.ReadByte(); // not 100% on what this value is
byte swapTableLength = dataReader.ReadByte();
// read XOR key & swap table
byte[] XORKey = dataReader.ReadBytes(XORKeyLength);
byte[] swapTable = dataReader.ReadBytes(swapTableLength);
// calculate how much movie data remains after reading xor key and swap table
int movieDataLength = data.Length - (int)dataReader.BaseStream.Position;
// not sure yet
int smallerBytesToSwap = movieDataLength / SPECIAL; // smaller
int largerBytesToSwap = movieDataLength - (smallerBytesToSwap * (SPECIAL - 1)); // larger
// stage 1 - read remaining data from file and decrypt using XOR key
List<byte> decryptedDataByteList = new List<byte>();
for (int i = 0; i < movieDataLength; i++)
{
decryptedDataByteList.Add((byte)(dataReader.ReadByte() ^ XORKey[i % XORKey.Length]));
}
byte[] decryptedData = decryptedDataByteList.ToArray();
// stage 2 - load decrypted data into cs reader & perform byte-swapping to finish decrypting data
using (MemoryStream decryptedDataStream = new MemoryStream(decryptedData))
using (CourseSmartReader decryptedDataReader = new CourseSmartReader(decryptedDataStream))
{
for (int i = swapTableLength - 1; i >= 0; i--)
{
byte swapValue = swapTable[i];
// swap is only performed if value from SwapTable is different from current position in table
if (swapValue != i)
{
// not exactly sure what this is about
int bytesToSwap1 = (swapValue == (SPECIAL - 1)) ? largerBytesToSwap : smallerBytesToSwap;
int bytesToSwap2 = (i == (SPECIAL - 1)) ? largerBytesToSwap : smallerBytesToSwap;
int bytesToSwap = Math.Min(bytesToSwap1, bytesToSwap2);
int secondSwapPosition = swapValue * smallerBytesToSwap;
int firstSwapPosition = i * smallerBytesToSwap;
// read two sets of bytes to swap
decryptedDataReader.BaseStream.Position = firstSwapPosition;
byte[] firstSwapBuffer = decryptedDataReader.ReadBytes(bytesToSwap);
decryptedDataReader.BaseStream.Position = secondSwapPosition;
byte[] secondSwapBuffer = decryptedDataReader.ReadBytes(bytesToSwap);
// write bytes back to decrypted data array
Buffer.BlockCopy(secondSwapBuffer, 0, decryptedData, firstSwapPosition, bytesToSwap);
Buffer.BlockCopy(firstSwapBuffer, 0, decryptedData, secondSwapPosition, bytesToSwap);
}
}
}
// overwrite reference to data with our freshly decrypted movie data
data = decryptedData;
}
}
/// <summary>
/// Decryption routine - extracted from offline viewer code
/// </summary>
/// <param name="data">Byte List containing encrypted movie data</param>
private void DecryptMovieData(ref byte[] data)
{
// load encrypted data into cs reader
using (MemoryStream dataStream = new MemoryStream(data))
using (CourseSmartReader dataReader = new CourseSmartReader(dataStream))
{
byte XORKeyLength = dataReader.ReadByte();
byte SPECIAL = dataReader.ReadByte(); // not 100% on what this value is
byte swapTableLength = dataReader.ReadByte();
// read XOR key & swap table
byte[] XORKey = dataReader.ReadBytes(XORKeyLength);
byte[] swapTable = dataReader.ReadBytes(swapTableLength);
// calculate how much movie data remains after reading xor key and swap table
int movieDataLength = data.Length - (int)dataReader.BaseStream.Position;
// not sure yet
int smallerBytesToSwap = movieDataLength / SPECIAL; // smaller
int largerBytesToSwap = movieDataLength - (smallerBytesToSwap * (SPECIAL - 1)); // larger
// stage 1 - read remaining data from file and decrypt using XOR key
List <byte> decryptedDataByteList = new List <byte>();
for (int i = 0; i < movieDataLength; i++)
{
decryptedDataByteList.Add((byte)(dataReader.ReadByte() ^ XORKey[i % XORKey.Length]));
}
byte[] decryptedData = decryptedDataByteList.ToArray();
// stage 2 - load decrypted data into cs reader & perform byte-swapping to finish decrypting data
using (MemoryStream decryptedDataStream = new MemoryStream(decryptedData))
using (CourseSmartReader decryptedDataReader = new CourseSmartReader(decryptedDataStream))
{
for (int i = swapTableLength - 1; i >= 0; i--)
{
byte swapValue = swapTable[i];
// swap is only performed if value from SwapTable is different from current position in table
if (swapValue != i)
{
// not exactly sure what this is about
int bytesToSwap1 = (swapValue == (SPECIAL - 1)) ? largerBytesToSwap : smallerBytesToSwap;
int bytesToSwap2 = (i == (SPECIAL - 1)) ? largerBytesToSwap : smallerBytesToSwap;
int bytesToSwap = Math.Min(bytesToSwap1, bytesToSwap2);
int secondSwapPosition = swapValue * smallerBytesToSwap;
int firstSwapPosition = i * smallerBytesToSwap;
// read two sets of bytes to swap
decryptedDataReader.BaseStream.Position = firstSwapPosition;
byte[] firstSwapBuffer = decryptedDataReader.ReadBytes(bytesToSwap);
decryptedDataReader.BaseStream.Position = secondSwapPosition;
byte[] secondSwapBuffer = decryptedDataReader.ReadBytes(bytesToSwap);
// write bytes back to decrypted data array
Buffer.BlockCopy(secondSwapBuffer, 0, decryptedData, firstSwapPosition, bytesToSwap);
Buffer.BlockCopy(firstSwapBuffer, 0, decryptedData, secondSwapPosition, bytesToSwap);
}
}
}
// overwrite reference to data with our freshly decrypted movie data
data = decryptedData;
}
}