In asymmetric encryption, which key encrypts and which decrypts?

The receiver's public key encrypts and the receiver's private key decrypts — anyone can send Bob a confidential message, but only Bob can read it.

How it works:

• Bob publishes his public key $K_{pub,B}$
• Alice encrypts: $c = E(K_{pub,B}, m)$
• Only Bob can decrypt: $m = D(K_{priv,B}, c)$

Key insight: Alice encrypts with Bob's public key. Only Bob's private key can decrypt. This solves the key distribution problem — no shared secret needed.

Go deeper:

• Public-key cryptography — the public-encrypt/private-decrypt direction.