Which type of cryptography are PGP, SSL, and IKE examples of?

• A. Symmetric key cryptography
• B. Hybrid cryptography
• C. Public key cryptography
• D. Hash-based cryptography

Answer: (C)

Public key cryptography relies on a pair of keys: a public key that can be shared openly and a private key kept secret. This setup lets you encrypt data or verify signatures with the public key, and decrypt or sign with the private key. PGP, SSL, and IKE all use this approach to bootstrap secure communication.

In PGP, a message is not encrypted directly with the recipient’s public key for the bulk data. Instead, a random symmetric session key is encrypted with the recipient’s public key, and that session key then encrypts the actual message. This is why PGP is often described as leveraging public-key cryptography to exchange a symmetric key securely.

In SSL (TLS), the handshake uses public-key cryptography to authenticate identities and to securely establish a shared session key. Once that key is agreed upon, symmetric encryption protects the data flow for performance.

In IKE, peers authenticate using public-key credentials and negotiate a shared key (often through Diffie-Hellman or digital signatures) that secures the IPsec traffic that follows with symmetric encryption.

So, the common thread is the use of public-key cryptography to establish trust and a secure key for subsequent data transfer. The scenarios wouldn't rely solely on symmetric-only methods, and the role of hashing is secondary to authentication and key exchange in these protocols.