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Re: IOS Rookit: the sky isn't falling (yet)
On Tue, 27 May 2008 19:49:21 BST, michael.dillon@xxxxxx said: > > Like MD5 File Validation? - "MD5 values are now made=20 > > available on Cisco.com for all Cisco IOS software images for=20 > > comparison against local system image values." > > I would expect a real exploit to try to match Cisco's > MD5 hashes. Although there is a known attack against MD5 that will generate two plaintexts with the same (unpredictable) hash, there is as yet no known way significantly better than brute force to generate a file which hashes to a given hash. On the other hand, there have been multiple cases where vandals have replaced a file on a download site, and updated the webpage to reflect the new MD5 hash. If you were an attacker, which would you go with: 1) The brute-force attack which will require hundreds of thousands of CPU-years. 2) The super-secret attack that causes a collision to a given hash that none of the crypto experts know about yet. 3) 'md5sum trojan_ios.bin' and cut-n-paste that into the web page. > By all means, check those hashes after you download > them but I would suggest calculating a hash using an alternate > algorithm for later checking. You missed the point - if the *FILE* you downloaded from a webpage is suspect, why do you trust the MD5sum that *the same webpage* says is correct?