RC4 Stream Cipher alone secure enough?
February 10th, 2009
Recently I had a discussion with a good friend about RC4 and if it is still to be considered "secure" ?
If you search around you will find that the Algorithm is still used very widely but often only in combination with other techniques like RC4-HMAC (hello! Microsoft), RC4-MD5 etc.
This document for instance from RSA Labs for instance is posted in the ``History'' section of their Homepage. This has a good reason.
The OpenSSH guys already kicked this Cipher out during development of early versions when they realized that SSH-1 used this Cipher wrong. This Cipher was also used in the e.g. WEP Protocol and was a disaster. (read: real-time decryption)
Now you will scream foul, we already know all that. For that purpose we have RC4-Drop ! It avoids all those bad, weak, keys and works fine. Cryptographically secure.
Admitted, you create a more secure version of this flawed Algorithm. I mean if you take into account all recent papers on Cryptanalysis and
monkey-patch your Algorithm to drop at least 3^H256 byte, figure out the weak keys from a generated subset (ref, many more papers until 2008) and then also make sure that you don't transfer too much data with this key, then you are probably on the safe side.
Let me ask this curious question, why do you want to use this Cipher? You will probably tell me you need alot of speed in your application and you don't care that projects like eStream and alike have been created (anno 2004) to address these problems? See Rabbit. This thing is really neat!
On the other hand if you really go with standard these days you will probably pick AES (128-bit) in Stream mode. I'm not a crypto expert so please be kind with your comments.
Other references:
- Paper on a good RC4 Attack (".. It is still successful if the first 256 bytes of the RC4 pseudo random sequence are not observable.")
- Interesting talk about Stream Ciphers during the 25C3
- New Stream Cipher HC-256
- CryptoBenchmark
- RC4 Description and brief analysis
2 Responses to “RC4 Stream Cipher alone secure enough?”
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February 10th, 2009 at 01:31 PM HN Comments: http://news.ycombinator.com/item?id=508824
February 26th, 2009 at 01:31 AM http://research.microsoft.com/en-us/people/mironov/rc4full.pdf http://research.microsoft.com/en-us/people/mironov/ http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html