RAID 6 uses 2 parity techniques to allow for up to 2 disks to become unreadable, an xor-based technique, and a Reed-Solomon-based one (which is based on Galois Fields). As a way to explore these I built this simple program based on a PDF from Kernel.org: https://www.kernel.org/pub/linux/kernel/people/hpa/raid6.pdf
Example output:
Original: 48 45 4c 4c 4f
Parity: 42 31
Missing Datum
48 45 4c 00 4f
48 45 4c 4c 4f
Pass: YES
Missing Dataum and XOR Parity
00 45 4c 4c 4f
48 45 4c 4c 4f
Pass: YES
Missing 2 Data
48 00 00 4c 4f
48 45 4c 4c 4f
Pass: YES