Already understanding that AES is the encryption method of choice, should existing code that uses DES be re-written if the likely threat is on the level of script kiddies? (e.g. pkzip passwords can be cracked with free utilities by non-computer professionals, so is DES like that?) A quick google search seems to imply that even deprecated DES still requires a super computer and large quantity of time--or have times changed?
In particular, this CAPTCHA library uses DES to encrypt the challenge string which is sent to the user in viewstate.
DES is broken so far as storing sensitive data, and so I would certainly not use it in anything new, and would replace it in anything used for long term storage of any information of interest (data that someone would have a profit for national security interest in stealing).
At the moment a DES message can be broken by brute force in a couple of days (or less) using under $100,000 worth of custom hardware.
But there are some key factors in that:
The hardware is custom - the chips used to quickly brute a DES key are not the general purpose processor you'd find in a PC. That being said there is probably room today for using a cluster of Playstation 3s or current generation graphics cards with a GPGPU to crack a DES message in a reasonable amount of time, perhaps bringing down the cost to maybe $15,000.
The other factor is time - a DES message can be cracked in a day, but if your CAPTCHA library has a timestamp that specifies a 30 minute timeout for any given CAPTCHA response, it would still be effective (you could scale up your hardware, but then you're talking millions).
Overall I'd say that for non-long term storage, DES is still secure against "script kiddies".
no, DES cracking is not suitable for scriptkiddies and won't probaly be in the near forseeable future.
it requires such enormous processing power, we're talking about a load of FPGA processors.
for example the COPACOBANA in the CHES 2006 secret key challenge took 21 hours, 26 mins, 29 secs using 108 of it's 128 processors, at a troughput of 43.1852 billion keys per second, and found the key after searching trough 4.73507% of the keyspace
now, if we look at moores law we see, that if we currently build a similar machine, it'll currently take 1/4th of the time for the same amount of money, or 1/4th of the money for the same amount of time.
DES is broken by the standards of the crypto community; but the time required to break it is generally large enough that it would be 'safe' to use for this kind of application. On one assumption: the DES key changes from session to session. If the key doesn't change, then it is open to attack by a very very dedicated individual. Now, the question is, is your website subjected to people that will spend 10+ days cracking DES, rather then applying lessons learned by the rest of the Spam Industry in the way of Image Recognition.
DES is probably still good enough for most use cases. But the point is, there is normally reason to use an algorithm (or in this case rather: a key strength) which is known to be rather weak. Wikipedia points out that even with special hardware around 9 Days are needed for an exhaustive key search. I don't think the script kiddies are likely to spend that many CPU time (even if they have a botnet) only to crack a captcha. (Actually, cracking captchas is normally A LOT easier with sufficient intelligent picture recognition...)
来源：https://stackoverflow.com/questions/1212563/time-to-crack-des-is-it-a-task-suitable-for-a-script-kiddie-yet