Latest stream cipher considered reasonably secure & easy to implement?

Question

(A)RC4 used to fit the bill, since it was so simple to write. But it's also less-than-secure these days.

I'm wondering if there's a successor that's:

• Code is small enough to write & debug within an hour or so, using pseudo code as a template.
• Still considered secure, as of 2010.
• Optimized for software.
• Not encumbered by licensing issues.

I can't use crypto libraries, otherwise all of this would be moot. Also, I'll consider block algorithms though I think most are pretty hefty.

Thanks.

Answer 1

No cipher is easy to implement, especially symmetric ciphers and they never will be. There is a lot that can go wrong, and most programmers don't realize this. You need to do a lot more reading into this topic.

With block ciphers you must be concerned with the mode you use, and different modes fill different needs(But ECB is always the wrong choice). You must also be very careful about maintaining a unique IV for each message. If you are using a "password" as your key then you have to use a string2key function.

Stream ciphers don't have IV's or modes, and this actually makes things more difficult. A stream cipher function accepts only a key and the output is a "PRNG stream" that is infinity large. This stream of random data is then XOR'ed with your message. So if you use the same key, you will get the same PRNG stream. If an attacker knows the plain text of 1 message (or a part of a message) then he can XOR out the PRNG from the cipher text and then decrypt all other messages using that key in constant time O(1). For a stream cipher to be practically secure you can never reuse the same key.

I highly recommend that you pick up a copy of Practical Cryptography, which has a few chapters dedicated to Symmetric Cipher attacks. This book is straight to the point and doesn't require a lot of math. If don't really care about implementing your own then you can use a proven cipher implementation such as Jasypt which "just works" in a very secure way.

Answer 2

Honestly your best bet is to go use a crypto library. Its an already tested platform and when even the crypto libraries can/do have trouble with implementing the algorithms... Its better to use the pre-existing crypto libraries, its already tough enough to do encryption/decryption correctly using the API as it is as in this post on Coding Horror: Why Isn't My Encryption.. Encrypting?

Now I've gone to the Wikipedia article on Stream ciphers it might be worth going through the list of ciphers on the article, there has been several ciphers developed since RC4 in 1987, and to my very limited cryptography knowledge some of them seems like they might be more secure than RC4. You may also want to consider checking out the Wikipedia article on eSTREAM. There are several ciphers which are in the portfolio: HC-128, Rabbit, Salsa20/12, SOSEMANUK.