Practice What You Are Most Likely to Forget.

Root Cause: Attackers deployed malware inside the SWIFT Alliance Access (SAA) server to manipulate local Oracle database records and intercept confirmation printer logs. Because the core cryptographic private keys for digital signatures were handled via hardware tokens on isolated rails, 30 out of 35 fraudulent payment orders were halted when signature origin verification failed.

┌──────────────────┐               ┌──────────────────┐
│  SENDER (ALICE)  │               │  RECEIVER (BOB)  │
├──────────────────┤               ├──────────────────┤
│ Message Plaintext│               │ Message Plaintext│
│        │         │               │        │         │
│  [SHA-256 Hash]  │               │  [SHA-256 Hash]  │
│        │         │               │        │ (Match?)│
│ + ALICE PRIV KEY │ ──Signature──►│ + ALICE PUB KEY  │
│        ▼         │               │        ▼         │
│[Digital Signat.] │               │ [Extracted Hash] │
└──────────────────┘               └──────────────────┘
* Mathematical Invariant: Only Alice possesses Private Key. Authenticity Proven.

Common Exam Trap: Candidates often confuse Integrity with Non-Repudiation.
• Symmetric HMAC: Guarantees Integrity & Authenticity between 2 trusted parties, BUT Alice can claim Bob created the message because Bob knows the shared secret.
• Digital Signature: Provides True Non-Repudiation because the private key is held exclusively by one entity.