What is the difference between a "leichte Störung" (light disturbance) and a "starke Störung" (heavy disturbance) when data is transmitted, and why does it matter for integrity checks?

A light disturbance flips a bit or two; a heavy one mangles whole chunks — and your integrity check has to be strong enough to catch both.

When Alice sends a file to Bob, noise on the line can corrupt it:

• Leichte Störung — a few bits flip. A simple checksum is usually enough to notice.
• Starke Störung — large parts are garbled. You need a method whose output changes drastically even for small input changes, so corruption can't slip through.

The core idea of integrity: Bob needs a way to tell "is what I received exactly what Alice sent?" He computes a check value over the received data and compares it to the one Alice attached. If they differ, the data changed.

Tip: Integrity ≠ confidentiality. We're not hiding the data here, just detecting whether it was altered.