LesS/KEY

This is a project to build a password management tool based on the S/Key system described in the RFC2289. This password manager is made with following goals in mind:

1. Passwords need to be memorable, secure and easy to type on any keyboard.

   The passwords which are generated with LesS/KEY can be easily memorized and used without the generator. Generate the passwords only if you forgot a password, it reduces the number of times you enter your master password dramatically. You also don't need to remember all of your passwords, remember those you really use, for the rest use LesS/KEY. I have managed over 500 passwords with this password manager for years now and I memorized approximately 10 of often used used passwords.

2. It should work everywhere.

   In fact, you even do not require this particular tool, but can use any tool which is capable of generating S/Key SHA-1 passwords. So you have the guarantee, that you can generate the password also without access to this particular tool. For most UNIX systems you can install the skey or equivalent command, which also generate exactly the same passwords.

3. You should be able to use it in a safe way, even if the whole time you generate a password somebody look on your screen.

   With LesS/KEY you can generate your passwords securely, also if somebody looks on your screen and you are on a foreign PC. (do not generate passwords on devices that you do not trust!)

4. It should work offline and should never send anything through the network.

   Files from this repository and a browser are enough to use this tool, you do not need to install something. It is also usable on any smart phone or similar devices, also without permanent connection to the internet.

5. It should not store anything anywhere and should be also usable on foreign systems.

   This password manager doesn't store your passwords or the names somewhere, so you should write your password names down and it is safe to do so, names have no security value. You have here a store button, it stores the checksum of your password name and the checksum of the master password in your browser. If you use this feature, the system will show you whether you typed an already used name or already used master password. It helps avoiding typos in master passwords a lot.

Fully usable installation: https://ooke.github.io/sk/

To use it in a shell, you can take the Python implementation here:
https://github.com/ooke/lesskey/blob/master/lesskey.py

On *BSD systems you could also just use skey -t sha1 99 test3, it is usually preinstalled, but does not support different modes. For some strange reason, on Linux systems it is no easy way to install this tool, please use lesskey.py script from this repository instead.

General use case

This is password manager and a password generator, you need a main password (secret) and you can generate a password based on a name (seed). Typical usage:

1. Enter a name to the seed field, f.e. if you need a password for Amazon, just type amazon there. It is also possible to enter amazonXX with any number of X after the name, in this case the system will replace all X characters with a random number with maximum number of digits equals to number of X entered. This is usefull if you think to change the password on a regular basis, simply enter again XX and it will generate a new number and a new password. The format of the seed field is following:

     [prefix] <name> [length][mode] [seq] [desc]
   

   Samples:

        amazon            (same as: amazan R 99)
        amazon R 99       (simple name)
        amazon4 R 99      (more unique)
        amazon4 8B 99     (8 characters)
        @T amazon4 B 99   (with "@T" prefix)
   

   The name can be simply entered as string without spaces, default mode and seq will be added automatically.

   • <prefix> Optional string which will be appended to the generated password as it is. This string is useful only to comply with meaningless policy rules.

   • <name> The name to use for generating, all uppacase X characters at the end will be replaced by a random number. Use the numbers to make the names more unique and easier changable.

   • [length] Length is optional and specifies maximal number of characters the password should have.

   • [mode] The mode to use for generating: - R regular password - U uppercase password (fully S/Key compatible) - N mode R with - instead of spaces - UN mode N in uppercase - H password as hexadecimal string - UH mode H in uppecase - B password in base64 format - UB mode B in uppercase - D decimal format (digits only)

   • [seq] The S/Key sequence number, default is 99 and should only be changed if you really understand what you do.

   • [desc] Description of the name, if nothing entered, then the system will put the current date in there automatically. I copy paste new names always with the date, to know later the date I have generated the password on.

2. Enter your master password, press enter and you can directly copy your generated password from next field. After pressing enter or tab the generated password will be selected and ready to copy to clipboard. If you click on the button show, then the master password respective the generated password became visible. If the password was stored once, the button store became light blue and if the password with this seed was stored once, than it bacame green.

This password manager do not store any names or passwords and do not communicate with anything, all calculations are done within your browser. Common way is to write down the meta information about each generated password in a system, which you can access as easy as possible, like in a file. Personally I use Evernote for it, because I can access it through browser, on any smart phone through a app and also on the UNIX shell with the Evernote API. I store following information there:

• Exact seed I have used, with prefix and modes
• Date on which the password was generated or changed
• URL of the web page or something else to identify the system
• Login name, birthday entered and similar meta data to be able to login or recover password later

The seed has no security value, so you do not need to encrypt this information, only your secret should stay really secret.

Usually you do not need to change the seq part of the seed (usually 99), it is only needed if you use this password manager as a real S/Key calculator, playing with thin number without knowing what you are doing can lead to security problems.

S/Key usage

This password manager can also be used as a S/Key calculator, if you login to a system with enabled S/Key athentication method, then type the sequence number, seed and secret and copy/paste your password. Usually it looks like follows:

$> ssh [email protected]
Password [ otp-sha1 45 oute52436 ]:

From this example you would need to type folowing as seed:

oute52436 U 45

Warning: only SHA-1 S/Key mode is supported and S/Key is not always safe to use. Do not use it through unencrypted connections! (I know, S/Key was developed initally for this case, but trust me, you should not use unencrypted connections at all, never!)

This is usefull, if your need f.e. login through SSH to your server from a PC, which you do not fully trust (internet caffee f.e.). You should use then LesS/KEY on a device you trust, like your smartphone to generate the one time password and type it on this PC. Even if some body logs the keyboard, this password became invalid and useless after you typed it in. Man in the middle attack is still possible but it is very hard to do and to prepare and you are usually safe, as long you use encrypted connections.

Hierarchical passwords

It is possible to use multiple master passwords in a hierarhical way:

1. Type a root seed and your master-master password.

2. Press enter and type your child seed and copy generated password

The reason to use hierarchical passwords is to use different master passwords for different types of systems. Typically you memoize the generated master passwords and use it, instead of using the master-master password all the type. In this way, if you loose the master password you need only reset the passwords on a bunch of services instead of all services you have ever generated passwords for.

For example I use one master password for home, one for work and one for regular web pages. All of the master passwords are still generatable, but I memoize them and do typically never type the master-master password somewhere. I do also memoize the generated passwords for all important systems, but if I forget one (f.e. after a vacation) I can generate it again any time. Some times I do also forget the master passwords, but they can also be generated, only my main master-master password is something I need really care about.

Security considerations

This password manager was inspired by the XKCD commic:

Internally it generates SHA-1 checksum chained seq number of times from seed and secret concatenated together. The result is reduced to a 64 bit number with bitwise XOR and represented as 6 words, with the scheme from RFC2289. Other representations are simply different representations of this 64 bit number.

The SHA-1 is considered as insecure, because it is possible to generate multiple documents with same checksum. This weakness do not apply here at all, because the possibility to genarate multiple seed/secret combinations which creates same password is irrelevant for the use case here. It is still no known possibilty to generate your master password from password and seed you have used, so SHA-1 is absolutely safe to use here.

Also S/Key is considered as insecure, because it is unsafe to use it on unencrypted links. Do not use unencrypted links, interfaces or systems, whether S/Key nor OTP nor this password manager can not help you in such cases. Using the S/Key method for authentication is always MUCH more secure, than typing your real password.

Do not generate passwords on devices that you do not trust!