What is an adversary type?

Question

The term "type 1 adversary" was used and I was curious as to what determines the adversarial type's category? Is it a well defined term within the cryptographic community? Please note that I'm a beginner in this field.

Answer 1

There are (at least) two contexts where an adversarial type number might be given. The more famous is in Chosen Ciphertext Attacks (CCA). In these, an adversary is permitted to provide inputs to a decryption function keyed with a secret value unknown to them. In this case the type 1 adversary (CCA1) is only permitted to submit a collection of ciphertexts in one go, but a type 2 adversary (CCA2) is permitted to submit an adaptive sequence of ciphertexts where each ciphertext can be chosen after seeing the output of the previous function call. CCA2 is obviously stronger and most analysis these days assumes a CCA2 adversary. See wikipedia for background.

Another possibility is in Certificateless Public Key Encryption as outlined by Al-Riyami and Paterson. Here they define 2 CLE adversarial types: one (type 1) without access to a system master secret but who can update the "directory" of public keys and another (type 2) which can access the Key Generation Centre's master secret, but cannot update the directory. A formal definition is given in section 3.1 of the paper.

There may be other sources and it is not possible to tell which model your questions refers to without additional information.