Contents - Keywords - Search || InstantCrypt Home - Previous - Next

IDEA: A Not Supported Algorithm

This is never a problem if you created your own key(s) exclusively with InstantCrypt.

Problem:


Encryption programs of the PGP standard such as InstantCrypt can use different encryption/decryption algorithms (or "ciphers"). When you send your key to another person, this key carries with it a list of ciphers that the program it comes from supports. The encryption program of another person looks at this list of ciphers and picks one that it (the program) and your program both support when it sends you a message.


IDEA is one such encryption cipher. Unfortunately there is a patent on IDEA, and it is only royalty-free for non-commercial use. Therefore, InstantCrypt as a free program that cannot pay royalties does not use IDEA. In this it follows the practice of GPG, InstantCrypt's underlying encryption engine.


This is usually no problem, as a key produced by InstantCrypt's encryption engine GPG clearly states that IDEA should not be used. Other encryption programs honor that. However, if you import one of your own keys created by another encryption program that allowed the IDEA cipher (e.g., PGP from PGP Corp.), trouble lies ahead: for that key has a list of allowed ciphers including IDEA. Now other programs may send you encrypted messages using IDEA, and InstantCrypt cannot read them.


Solutions:


  1. Avoidance: Do not import one of your own keys created in another program unless you are sure IDEA is not on that program's list. Or:


  1. Correction: When importing one of your keys from another program, InstantCrypt warns you if this key has IDEA in the list of allowed ciphers. You should:


    1. Change the list of ciphers in the imported key, so that IDEA can be removed from that list. InstantCrypt asks you to do that when it imports such a key and it does not let you export a key with IDEA in this allowed-ciphers list before removing IDEA. (To change the list of ciphers you have to confirm your key ownership with the key's password.)
    2. Change the list of allowed ciphers for the copy of the key that is still in the other program, unless you never want to export your key from that program again.
    3. Re-distribute your key with the new cipher list if you sent out your key to other people or key servers before you made this change. Otherwise, the old copies of your key "out there" will tell the world that it is o.k. to use IDEA.