RC4 Safe to use plaintext as the key to encrypt itself?

Question

Basically what the title says. If I have a password, of say "APPLEPIE" is it safe to use "APPLEPIE" as the key when I RC4 it? Is it possible to break the RC4 encryption when you know the Key and Plaintext or are short and the same?

Answer 1

This should be handled with a key generation algorithm like PBKDF2, which will allow you to securely generate a hash from your password in a way that is appropriate for password verification (which is what I assume you're doing).

While it is possible to generate a system by which RC4 would be safe this way (by converting the password into an RC4 key using a good KDF (such as PBKDF2), and then generating a random nonce), this is a lot of overhead to no purpose. You'll wind up with a much longer final cipher text for the same level of security, and it'll take you longer to generate it. In the end, you'll have just created an extremely complicated secure hash function (whose first step is "do the only thing you needed to do anyway). And you'll probably have made a mistake along the way, making the system insecure. RC4 can be tricky to do correctly and has known related-key attacks; hence the break of WEP.