Password
The password of a level is the code that must be entered to unlock the level if that level has not already been unlocked. There are 456,976 (= 264) possible 4-letter passwords.
How to use passwords
MS
The password is indicated in the start screen for each level, just after the title. In the MS Chip's Challenge menu, a level number and/or password may be entered. If the level is locked, at least the password must be used, and if not, either or both can be used, with one special exception: if the level has been unlocked by Ignore Passwords, at least the level number must be used, as Chip's Challenge is programmed to search only within the list of locked levels if the password only is entered. Since the search turns up a level that does not exist, the Termination Glitch occurs.
Lynx
In the original Lynx version, a password can be entered in one of the opening screens, or the player can choose to start at Lesson 1. If the password is valid, the game will redirect the level with that password, and otherwise the first level will open. Unlike Tile World and MS, there is no in-game function for changing levels in the original Lynx version.
The Tile World Lynx version's passwords work the same as the MS Tile World: press G in-game to be prompted to enter a password.
Requirements
The password consists of a sequence of characters, not necessarily letters, between zero to nine characters long. Passwords above 9 letters long will cause an error in Chip's Challenge. It is customary, but not required, that the password consist of 4 uppercase letters, such as WXPB, as all CC1 passwords use this format.
Tile World will not play levels that have a password with less or more than 4 characters. In order for a level to be playable in Tile World, the password must be exactly 4 characters. Lowercase letters will not work in Tile World passwords (the level will still be playable but won't be accessible via password).
It is not required that every level set contain distinct passwords for each level, but in the event that two levels have the same password, the Go To dialog will redirect to the first level with the given password. In fact, Four Square and Paranoia, levels 95 and 96 in CC1, have the same password in the Microsoft version. In the Lynx version, some passwords are different, including these.
Password generation
The DOS and Spectrum ports of the Lynx version (and presumably the Lynx original and other ports) generate the level passwords procedurally, using a pseudo-random number generator. Although only 149 passwords are required, 256 are generated.
This process produces three duplicate passwords in the 1-149 range (for Shrinking, Balls O Fire, and Deception), so these three passwords are manually adjusted to be unique. It produces a further nine duplicates in the 150-256 range.