Re: scrypt: Decrypting file would require too much memory

[Christoph Borsbach <christoph+tarsnap@borsbach.org>]

On Fri, Oct 16, 2015 at 21:02:46 -0700, Colin Percival wrote:
> On 10/16/15 01:06, Christoph Borsbach wrote:
> > On Thu, Oct 15, 2015 at 13:33:30 -0700, Colin Percival wrote:
> >> The relevant limits value is the datasize, not the stacksize.  But to answer
> >> your question, scrypt uses a large amount of memory -- the larger the better
> >> -- to convert your passphrase into the key used for encryption; so this is
> >> entirely independent of the amount of data you're processing.
> > 
> > I have access to another OpenBSD System with 6 GB Ram. I cranked the datasize
> > limit to ~5GB and still I get the same error: 
> > 
> > $ ulimit -a
> > time(cpu-seconds)    unlimited
> > file(blocks)         unlimited
> > coredump(blocks)     unlimited
> > data(kbytes)         5316608
> > stack(kbytes)        4096
> > lockedmem(kbytes)    2026642
> > memory(kbytes)       6078248
> > nofiles(descriptors) 512
> > processes            256
> 
> Hmm, I wonder why scrypt thinks you don't have enough memory then.
> 
> > Anyway, do I understand the -M option to scrypt correctly that if I use, say,
> > -M 536870912 (512MB), on all of my machines, it should decrypt on all machines
> > (that have a ulimit of 512MB or more) without error? 
> 
> You'll need a slightly higher ulimit than that (since there is a small amount
> of memory used by other things), but yes, if you use -M to set a reasonably
> low limit everywhere then you should be fine.  If that doesn't work on the
> systems you've mentioned above, I definitely want to know.

Hi, 
with the -M option it works in all directions. Thanks for the pointers!

All the best,
Christoph