read XOR encoded blocks

[jbride]

1. Read raw (encrypted) bytes from the file
2. If an XOR key exists, decrypt each byte by XORing it with the corresponding key byte
3. Key bytes are used cyclically (if data is longer than key)
4. Convert decrypted bytes back to the desired data type

decode example:

	data
encoded data:	01111000
XOR Key:	10101010
decoded data:	11010010