Constructor that takes a password, salt, iteration count, and to-be-derived key length for generating PBEKey of variable-key-size PBE ciphers. An empty char[] is used if null is specified for password.

Note: the password and salt are cloned before they are stored in the new PBEKeySpec object.

Parameters:

password     the password.

salt     the salt.

iterationCount     the iteration count.

keyLength     the to-be-derived key length.

Exceptions:

NullPointerException if salt is null.

IllegalArgumentException if salt is empty, i.e. 0-length, iterationCount or keyLength is not positive.

`password`		the password.
`salt`		the salt.
`iterationCount`		the iteration count.
`keyLength`		the to-be-derived key length.

`NullPointerException`		if `salt` is null.
`IllegalArgumentException`		if `salt` is empty, i.e. 0-length, `iterationCount` or `keyLength` is not positive.