[erlang-questions] Erlang cookies are secure

Mike Oxford moxford@REDACTED
Sun Jun 12 01:56:50 CEST 2016

​​I've not looked into the Erlang use of the key, I'm only commenting on
the use of MD5 sums ...

MD5 effectively "normalizes" the input to a discrete output space, by
design, as the output length/set is finite.

​If MD5 is weak to hash-collisions (which it is, relatively) then I don't
need to spray the cluster with a single discrete value to get the command
accepted - the range of possibilities goes from "1" to "N" where "N" is the
discrete (but yet unknown) set of values which produce the collision.

You may have used a super high-tech and secure 2048-bit key but if it just
happens to collide with "password" then it'll be found relatively quickly.

Again, haven't looked at Erlang code to see how it's actually used in the
context of this discussion.



On Sat, Jun 11, 2016 at 2:54 PM, Per Hedeland <per@REDACTED> wrote:

> Ulf Wiger <ulf.wiger@REDACTED> wrote:
> >
> >We should be able to agree that:
> >
> >- the cookie strategy and challenge aren’t necessarily broken in
> principle
> >- the MD5 hash is a weakness which could be addressed
> >- using TCP opens up for eavesdropping and MITM attacks
> >- the biggest weakness is the (human) practice of using hard-coded simple
> cookies for convenience
> >- little (albeit some) support exists for applying a more sophisticated
> cookie management strategy
> >- The simplest advice to heed is “don’t expose your dist ports to
> strangers"
> I can agree to all of that, except that I'm not sure that the "weakness"
> of MD5, which pertains to its ability to produce a digest of a cleartext
> that can't be reproduced by applying it to a different cleartext, even
> when the original cleartext is known (i.e. the case of using a digest +
> signature to ensure integrity), is significant in this particular
> context. And unfortunately that's the only one of your points that
> addresses the security of the cookie authentication mechanism as such...
> --Per
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