I read about PBKDF2 on Wikipedia and seen few apps. having option to manually enter number of iterations. I am still not clear on this.
(1) With what I understood, key iterations can be used only with symmetric encryption. If a file/text is encrypted using passphrase, HASH is calculated and encrypted with AES for 'n' number of times. If iterations selected is 100 then this is done 100 times. This is done to defend against brute-force attack.
(2) Key iterations have no use with public-key encryption.
(3) Some apps. by default take 100 iterations. Few apps by default takes 2000 iterations when using AES. How many iterations are considered secure with AES-128 and AES-256?