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

Secret key cryptography refers to symmetric encryption (e.g., AES, DES) where both parties share the same key - SSL, IKE, and PGP use symmetric ciphers only after asymmetric key exchange is complete.

Hash algorithms (e.g., SHA-256, MD5) are one-way functions used for integrity verification, not for the encryption and key-exchange mechanisms that define SSL, IKE, and PGP.

A digest is the output of a hash function and is used for integrity checking, not for the asymmetric encryption and key management that SSL, IKE, and PGP perform.

Public key cryptography uses mathematically linked key pairs - a public key and a private key - where data encrypted with one can only be decrypted by the other. SSL/TLS uses RSA or ECDSA certificates for server authentication and asymmetric key exchange; IKE uses Diffie-Hellman asymmetric exchange to establish shared session keys; and PGP uses RSA or DSA for signing and encrypting messages. All three fundamentally depend on asymmetric algorithms.