Which type of cryptography does SSL, IKE and PGP belongs to?

Secret key (symmetric) cryptography uses a single shared key for both encryption and decryption; while SSL and IKE negotiate symmetric session keys after the handshake, the protocols themselves are classified under public key cryptography for their core authentication and key exchange mechanisms.

Hash algorithms are one-way mathematical functions such as SHA-256 or MD5 that produce a fixed-length digest; they are not encryption mechanisms, and SSL, IKE, and PGP are not categorized as hash algorithms.

A digest is the fixed-size output produced by applying a hash algorithm to input data and represents a fingerprint, not a category of cryptographic system to which SSL, IKE, and PGP belong.

Public key cryptography uses a mathematically related key pair - a public key for encryption and a private key for decryption - enabling secure communication without requiring a pre-shared secret. SSL/TLS uses public key cryptography during the handshake to authenticate the server and negotiate symmetric session keys, IKE uses digital certificates or public keys to authenticate IPsec peers during tunnel establishment, and PGP uses public/private key pairs for email encryption and digital signatures. All three are canonical examples of asymmetric cryptographic systems.