Several cryptographic models provide adequate means for proving the security of protocols.
If the adversary has limited resources (polynomially bounded), then the model is based, either on pseudorandomness and we have proven security, or the security is reduced to a problem which is (believed to be) intractable. The strength of the cryptographic approach lies, essentially, in its flexibility.
Depending on the security requirements and the model, we can use appropriate cryptographic attributes such as zero-knowledge or indistinguishability, as a tool to design secure protocols. We will discuss practical network protocols whose security can be proved in an appropriate cryptographic model.