Re: scrypt: Decrypting file would require too much memory

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

On Wed, Oct 14, 2015 at 19:52:30 -0700, Colin Percival wrote:
> On 10/14/15 00:45, Christoph Borsbach wrote:
> > I have a simple question regarding the scrypt utility. I use it to encrypt
> > and decrypt a small textfile, which changes from time to time. Since the last
> > change I made to the file I get the following error when I try to "dec" the
> > file: 
> > 
> > scrypt: Decrypting file would require too much memory
> > 
> > I tried to play around with the -m and -M options, but no matter how much
> > memory I grant scrypt, the error persists. This is scrypt-1.1.6 on an OpenBSD
> > 5.7 system. Now, the same file decrypts fine on an Ubuntu Linux System with
> > scrypt 1.1.6., so I can get to the data, no problem. The file is very small,
> > just a 100 lines of test, if that. 
> 
> How much memory does this system have?  Did you encrypt the file on the same
> system?  If you encrypt a new file now, can you decrypt it?  Has anything
> changed on the system since you encrypted the file?

The system has 2GB of memory and I can encrypt and decrypt new files just
fine. But I traced my steps and I actually did the last encryption on another
system: scrypt 1.2 on OSX. (I actually forgot that). So that might be it? It
is still a bit strange that I can decrypt the file on Linux and scrypt 1.1.6.

Thanks! 
Christoph

> The scrypt code makes some awkward attempts to figure out how much memory is
> "available"; unfortunately there isn't any really good way to figure this out
> (and indeed the concept isn't even entirely well-defined).  The most likely
> scenario here is that the scrypt code is thinking that you have very little
> available memory.
> 
> -- 
> Colin Percival
> Security Officer Emeritus, FreeBSD | The power to serve
> Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid