Authentication Requirements
1. What Must Authentication Prove? (beginner!)
When Bob gets message "Pay ₹1000" claiming to be Alice, he must verify TWO things: who sent it (authenticity!) + was it changed (integrity!). Plus disputes need non-repudiation (sender can't deny!) and freshness (not an old replay!).
2. Four Requirements (exam list!)
| Requirement | Question answered | Attack blocked |
|---|---|---|
| Authenticity | really from Alice? | masquerade (Eve pretends!) |
| Integrity | modified in transit? | tampering (bit flips!) |
| Non-repudiation | can Alice deny later? | denial (need proof for judge!) |
| Freshness | new or replayed? | replay (old message resent!) |
masquerade: Eve sends "Pay Eve ₹5000" as Alice → need signatures/MAC!
tamper: Eve flips ₹1000 → ₹9000 → need hash/MAC check!
replay: Eve resends yesterday's "Open door" → need nonce/timestamp!
deny: Alice sends order, later denies → need signed proof!
5. Exam Points
- Four requirements + attack each — 5-7 marks, very frequent opener.
- Hash vs MAC vs signature coverage — 5 marks, favourite map.