Is it safe to rename file.gpg to `md5sum file`?
sben1783 at yahoo.de
Wed Dec 5 22:39:04 CET 2012
Am 05.12.2012 18:59, schrieb Max Parmer:
> On Tue, Dec 4, 2012 at 12:03 PM, sben1783 <sben1783 at yahoo.de> wrote:
>> Yes, I meant to use the MD5 checksum of the original file, not its
>> original name. I'm still interested whether this would be "insecure"?
> If by insecure you mean, "could lead to exposing the contents of the file"
> or "could reveal my passphrase" that would depend (in part) on the size and
> contents of the file (i.e. very short files would less time consuming to
> brute force, files with very regular formats would be quicker to brute
> force, etc.) and the symmetric cipher used.
Yes, that's exactly what I meant with "insecure". So I learn from your
statement to better not use the md5 hashes.
> Revealing the plaintext of some files could be fairly significant with the
> default symmetric cipher for GPG is CAST-128 which is potentially subject
> to key recovery via a chosen plaintext attack. AES doesn't have any
> presently known vulnerability of that sort.
While browsing for recommandations on what algorithm to use, I didn't
come across the "vulerability" you mention above. I don't really
understand what you're saying, but anyway plan to use AES because it a)
seems to be the algorithm "more state of the art" and b) uses MDC by
> If you just need a unique key to refer to the file, you're already storing
> the source path in the "summary" file your tool generates. If you just need
> a guaranteed unique identifier for each file (because, say, you're storing
> them all flatly in a single directory), I would just hash the path (which
> is apparently not sensitive data, as you seem to be storing it in plaintext
> in the summary file) as it's guaranteed to be unique per-system.
Well I do *not* want to reveal my private paths/filenames in the remote
backup location. I won't upload the summary file as plaintext, but maybe
encrypted as contents.gpg or the like. So I need another identifier for
each file and some sort of mapping. That's why I came up with the md5sum
of the files contents in the first place - I already have the mapping
table (the summary file). If that's no good idea, I will probably just
use a GUID for each file and create a separate mapping table (which also
won't get uploaded without encryption:)
If I wanted to have a fallback for loosing the mapping table, would
there be a sane way to encrypt the filename with gpg? That way I could
decrypt it in case I loose the mapping table (which isn't possible with
the GUID solution). I tried
echo '/path/to/original/filename' | gpg --armor -c
but the result contains newlines and slashes which isn't good for use as
filenames. There's no option like "--armor-only-alphanumeric"...?
Thank you very much
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