Identity-Based Encryption. Stanford University – Identity-Based Encryption.
With IBE, if Alice wants to send Bob an encrypted message, she simply encrypts using Bob's email address. Thus Bob's email address is his public key; there is no need for Bob to use cryptography software to generate a public key, nor does Alice have to retrieve a public key from Bob, or from a directory service.
Once Bob receives an encrypted message, he retrieves his private key from the trusted server (he only has to do this the first time) and then decrypts.