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What is the minimum safest length when using MD5? I remember seeing 14 somewhere but I cant find the citation. Not forcing everyone to use 14 chars of course
by binarymax 16y ago
What is the minimum safest length when using MD5? I remember seeing 14 somewhere but I cant find the citation. Not forcing everyone to use 14 chars of course but adding salt.
- rmc 16y agoDon't use MD5. This only gets faster, not slower. No matter how much you salt your passwords, soon they will be able to crack your passwords fast enough. And soon there will be rainbow tables of salts.
- Aleul 16y agoWhat would you recommend doing then? (New to this stuff)
- rmc 16y agoI suspect tptacek will come in with some sound advise. But bcrypt seems to be the way forward. cf. http://codahale.com/how-to-safely-store-a-password/ http://codahale.com/how-to-safely-store-a-password/
- sparky 16y agobcrypt or scrypt (http://www.tarsnap.com/scrypt.html http://www.tarsnap.com/scrypt.html). bcrypt lets you more or less arbitrarily set the computational complexity (in terms of instructions) of key generation. scrypt is newer (2009), but has the attractive property that it lets you arbitrarily set the memory complexity instead (how much memory it takes). This is attractive because key generation with a large memory requirement is more expensive to massively parallelize with an ASIC/FPGA farm. If you have a seriously good reason for not using either of these, which you probably don't, "stretched" (iterated thousands of times) and salted SHA-2 or MD5, or PBKDF2 ( http://en.wikipedia.org/wiki/PBKDF2 http://en.wikipedia.org/wiki/PBKDF2 ) can be acceptable alternatives.
- Aleul 16y agoThanks a bunch rmc, and sparky! I'll definitely be spending some time reading up on these tonight.
- rorrr 16y agoThat's just not true. If your salt is 1000 characters long, they will need more energy than the whole universe has to bruteforce it.
- tedunangst 16y agoExcept anybody playing this game has the salt, there's no need to guess it.
- ent 16y agothe point of adding a salt to the passwords is not to make decrypting the individual passwords harder - the salts are kept in plaintext - but to make it impossible to prevent the use of rainbow tables. that is, having longer salts will only make it harder for finding out all the people with the same password.
- rorrr 16y agoThat's assuming hacker knows the salt, which is not always the case.
- rmc 16y agoMy prediction: After there are loads of MD5 rainbow tables with all the passwords a human could use, people will make rainbow tables with salts. First one byte of salt, then two. Granted this gets exponentially harder, but eventually it'll be close.