We discussed public key cryptography, and certification by a trusted authority as a means of key distribution in public key cryptography. There is also an emerging paradigm called identity-based cryptography, which works as follows. Each user sets its public key as its identity ID (such as an email address); obtains a signature of a trusted authority on its public key and set this signature as its private key. The users can use the public key and private key pairs for secure communication with each other (everyone needs to know the public key of the trusted authority to do so, as in the public-key cryptography).

Compare the identity-based cryptography with the public-key cryptography (say which one is better and explain why), in terms of the following:

1. Security of the joining process (which is the process of obtaining a certificate in public key crypto, and a signature in identity-based crypto)

2. Cost of key generation on the user

3. Level of trust on the trusted authority

4. Usability of secure communication (both for confidentiality and authentication)

5. Revocation