F2 Data representation and bit operations

Needs: Supporter

Lesson F2: Hex, binary, BCD, ASCII and EBCDIC, XOR and bit numbering: the encodings behind most payment bugs.

This is a supporter feature. Create a free account, then try every supporter feature free for 7 days.

Sign in

Create a free account

See plans

The opening of the lesson

Why it matters

The same twelve-digit amount can travel as:

twelve ASCII bytes;
six packed-BCD bytes;
twelve EBCDIC bytes.

A key can be shown as hex text or used as binary bytes. Most "the MAC is wrong" or "the PIN fails" bugs are not cryptography bugs at all: they are encoding bugs. Being fluent in hex, BCD and XOR saves days.

In the full lesson

The concept
Step by step
In the real world
Common mistakes
What to test

What module F2 covers →

The rest of the lesson opens with a supporter pass, which you can try free for 7 days.