7-zip broken password random number generator
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7-zip broken password random number generator
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Re: 7-zip broken password random number generator
#2> Open-source "many eyes have looked at it for years so it must be secure" crypto code.
Nobody claims this. Open source code is just easier to audit than non-open code.
Re: 7-zip broken password random number generator
#3not a cryptographer: but from memory the main quality important in an IV for CBC is that it isn't reused for the same key (chosen plain-text attacks aside)
so that routine... while far from ideal would seem to mostly satisfy that property if you are making zip files of your own data to send to people (unless you use the same key rather a lot)
Re: 7-zip broken password random number generator
#4not a cryptographer: but from memory the main quality important in an IV for CBC is that it isn't reused for the same key (chosen plain-text attacks aside) so that routine... while far from ideal would seem to mostly satisfy that property if you are making zip files of your own data to send to people (unless you use the same key rather a lot)
Correct, the guy on twitter doesn’t seem to know what he is talking about.
Random IVs in CBC mode are an easy way to be fairly sure that you wont accidentally repeat a key+IV without much effort, but there is no security dependency on it being random nor on it being secret.
Re: 7-zip broken password random number generator
#5It is not clear if anything is actually wrong here. It would be nice if someone who has spent more than "30 minutes" looking at this code could verify these claims and publish an article explaining the implications of these design choices.
The twitter thread that this is aggregated from has replies that seem to indicate that there is no practical exploit here.
Re: 7-zip broken password random number generator
#6> Open-source "many eyes have looked at it for years so it must be secure" crypto code. Nobody claims this. Open source code is just easier to audit than non-open code.
Yes, and the article itself is an example of this.
Re: 7-zip broken password random number generator
#7>I thought about reporting this at 7zip Sourceforge forums but then I vomited again when I saw a long thread of largely incoherent exchanges on how 7z should be using Twofish instead of AES-256 because...
Just because a bunch of tinfoils are arguing over whatever doesn't mean you shouldn't still report it! Just be sure to word the report more generic than usual so the hordes don't find the issue and turn it into a battleground before a serious maintainer can get to it
Re: 7-zip broken password random number generator
#8> Open-source "many eyes have looked at it for years so it must be secure" crypto code. Nobody claims this. Open source code is just easier to audit than non-open code.
Well, in the past it was one of the main arguments in favor of open source. There is even a related article on the WP: https://en.wikipedia.org/wiki/Linus%27s_Law (it has nothing to do with Linus though)
Re: 7-zip broken password random number generator
#9It is not clear if anything is actually wrong here. It would be nice if someone who has spent more than "30 minutes" looking at this code could verify these claims and publish an article explaining the implications of these design choices. The twitter thread that this is aggregated from has replies that seem to indicate that there is no practical exploit here. https://twitter.com/3lbios/status/1087848040583626753
On the other hand, using the system cryptographic RNG (/dev/urandom, CryptGenRandom) is probably less effort than it took to write this strange half-baked RNG.
Re: 7-zip broken password random number generator
#10The attack here is:
1) You encrypt two pieces of data within the same second in the same process (so probably using the library?)
2) or if you're using the command-line, the attack is you encrypt two pieces of data within the same second, and somehow wrap-around your pid within the second to get the same pid again.
That may be enough, or not enough -- but for those that claim that's not enough, one needs to recognize the cognitive dissonance with reusing the same password
A monotonically increasing integer as IV is perfectly fine, and this dude is a bit out of his depth thinking IVs need to be random.