PGP, SSL, and IKE are all examples of which type of cryptography?

A digest refers to the output of a hash function, not a type of cryptography itself.

Secret key (symmetric) cryptography uses the same key for both encryption and decryption, whereas the listed protocols primarily use asymmetric methods for initial key exchange and authentication.

PGP (Pretty Good Privacy), SSL (Secure Sockets Layer, now TLS), and IKE (Internet Key Exchange) are all protocols that extensively use public key cryptography. Public key cryptography, also known as asymmetric cryptography, employs a pair of keys-a public key for encryption and a private key for decryption-enabling secure key exchange and digital signatures without prior sharing of a secret.

Hash algorithms produce a fixed-size output (hash or digest) and are used for integrity checks, not for encryption or key exchange in the way PGP, SSL, and IKE primarily function.