Asymmetric encryption
Encryption using different keys: public key for encryption, private key for decryption. Enables secure communication without prior key exchange. Slower than symmetric.
Formula
C = E(K_public, P); P = D(K_private, C)
Real World
When you visit Amazon.co.uk over HTTPS, your browser uses Amazon's public key to encrypt a session key that only Amazon's private key can unlock, establishing a secure channel without you ever sharing a secret in advance.
Exam Focus
Clearly distinguish which key encrypts and which decrypts — swapping them is the most common lost-mark error.
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