There are 8 fundamental attacks: eavesdropping, modifying, inserting, replaying, deleting messages, plus denying sending, denying receiving, and masquerading as someone else.

* The classic Alice / Eve / Bob model: 5 channel attacks, 2 repudiation attacks, 1 identity attack. *

The attacks target a channel between sender Alice (A) and receiver Bob (B), with attacker Eve (E):

Tip: Group them as: 5 channel attacks (1-5), 2 repudiation attacks (6-7), 1 identity attack (8).

Go deeper:

• Information security (CIA triad) — the confidentiality/integrity/availability goals these attacks target.

Three security requirements — confidentiality, data integrity/authenticity, and user authenticity — each protect against specific subsets of the 8 attacks.

* Each requirement defends a specific subset of the 8 attacks. *

Notice that data integrity/authenticity covers the largest group (6 attacks). This is why MAC and digital signatures are so central to cryptographic protocols — they handle most of the threat landscape.

What about availability? It's deliberately absent from this model. The classic crypto model scopes the goals cryptography can enforce on a message — confidentiality, integrity/authenticity, and user authenticity. Availability (keeping a service reachable, surviving a DoS) is a systems/network property that crypto can't deliver: encrypting or signing a message does nothing to stop it being dropped or a server being flooded. It's part of the broader CIA triad, but it sits outside the cryptographic requirements.

Go deeper:

• Information security — how security goals partition the threat space.