Re: Looking for simple wrapper for symmetric key file encryption

[Mr. Clif]

Hi Doug,

Thanks for the comments. Yes the threat model is mostly the worry of 
having old temp files or even the original cleartext files left behind 
on the HD, or even worse having them backed up. ;-) At the very least I 
want something that tries to protect me from stupid mistakes. Yep the 
RAM disk idea was part of the solution I'm heading towards.


So do you or does anyone know of a nice front end that helps with that? 
An example of behavior that doesn't seem helpful is that when I use GPA 
to decrypt a file it defaults to saving it on the HD. I'm not trying to 
knock GPA here but wouldn't it be better to display the contents in a 
window? Well I realize that might be just what I want, and others have 
use cases that it works fine for. ;-)


Clif

On 01/19/2014 01:23 PM, Doug Barton wrote:

On 01/19/2014 08:56 AM, Mr. Clif wrote:

So I'm trying to get a sense from the users here if they feel that the
process of using gpg for symmetric encryption is safe enough, and they
are not worried about leaving clear text behind.


I think you're misunderstanding a few things. First, the problem of 
the plain text file is not exclusive to symmetric encryption. In fact 
there is no difference between that, and the plain text file that's 
left behind after public key encryption.


Second, you haven't defined your threat model. You have given us a 
vague sense of wanting to have a "secure" system, but you haven't said 
what you're trying to secure it against. Thus it's hard to respond 
intelligently to your query.


That said, I would suggest that you consider using a RAM disk to do 
your work on. It can be created to do the work, then deleted after 
you're done, with no risk of leaving a file behind on disk. Of course 
you'd want to make sure your RAM disk was not swap-backed.


hope this helps,

Doug




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Re: Looking for simple wrapper for symmetric key file encryption

[Doug Barton]

On 01/19/2014 08:56 AM, Mr. Clif wrote:

So I'm trying to get a sense from the users here if they feel that the
process of using gpg for symmetric encryption is safe enough, and they
are not worried about leaving clear text behind.


I think you're misunderstanding a few things. First, the problem of the 
plain text file is not exclusive to symmetric encryption. In fact there 
is no difference between that, and the plain text file that's left 
behind after public key encryption.


Second, you haven't defined your threat model. You have given us a vague 
sense of wanting to have a "secure" system, but you haven't said what 
you're trying to secure it against. Thus it's hard to respond 
intelligently to your query.


That said, I would suggest that you consider using a RAM disk to do your 
work on. It can be created to do the work, then deleted after you're 
done, with no risk of leaving a file behind on disk. Of course you'd 
want to make sure your RAM disk was not swap-backed.


hope this helps,

Doug


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Re: Reusing signed user ID or attribute

[Daniele Ricci]

Thank you Daniel,
it actually sounds very right. Now that I think about it, storing this
kind of data in the public key block isn't so good afterall. I will
investigate over this and ask to the right ML next time.
Thank you everyone for your help.

On Sun, Jan 19, 2014 at 5:21 PM, Daniel Kahn Gillmor
 wrote:
> On 01/19/2014 09:55 AM, Daniele Ricci wrote:
>> Ok, so I have to conclude it's implementation specific?
>> I'm using a custom user attribute to store something that can change
>> quite often (privacy lists for a chat user). What do you suggest?
>
> I don't know what a "privacy list for a chat user" is.  You should
> probably try to document what you are trying to achieve more clearly,
> and present it in a public forum where people can help you think through
> possible ways to achieve it.
>
> This thread started off by asking about user IDs or attributes, which
> seems to assume that this is the only way to provide the information
> you're looking for.  But an OpenPGP notation (stored within the
> self-signature) could also provide that information directly.
>
> User IDs and User Attributes are for information that you need or want
> third parties to confirm and certify.  Information in an OpenPGP
> notation does *not* need to be confirmed or certified by third parties.
>  So if Alice wants to indicate something about her preferences about how
> to use chat, she can do so in a notation subpacket within her self-sig.
>
> does this make sense?
>
> --dkg
>
>



-- 
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Re: Looking for simple wrapper for symmetric key file encryption

[Mr. Clif]

On 01/19/2014 03:53 AM, Johan Wevers wrote:

On 19-1-2014 7:50, Mr. Clif wrote:


Does anyone use symmetric file encryption?

Yes, but only for encrypting files for personal use. Not in
communication with others.



Same here. This is why I wrote that perl script, so I wouldn't have to 
remember to delete the plaintext file after I encrypted it. Are there 
other front ends or wrappers that help the work flow in this way?




What is the best practice here?

As always, that depends on your use case and threat model.


I heard of another solution which was to mount an encrypted
directory with fuser to drop files into.

Possible, I use TrueCryot containers for that but that's similar
(although more portable and usable on "that other  OS").


I think I would wounder how
safe the passphrase was for mounted filesystems,

Are you asking how long it would take to brute-force the pasword, how
difficult it is to snoop it or if there are known vulnarabilities in the
symmetric encryption used by gnupg, fuser or others?


though I know of some techniques for protecting them.

Remember the weakest link in all encryption: https://xkcd.com/538/
Yes I suppose that's true. Though I was just thinking about ways I heard 
of to hide the key material in RAM. As I mentioned below, I'd rather not 
have to resort to an encrypted filesystem just to handle the occasional 
private file unless the conventional wisdom says that it's the only good 
way to do it.


So I'm trying to get a sense from the users here if they feel that the 
process of using gpg for symmetric encryption is safe enough, and they 
are not worried about leaving clear text behind.


Thanks,
Clif


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Re: Looking for simple wrapper for symmetric key file encryption

[Johan Wevers]

On 19-1-2014 12:12, Andy Ruddock wrote:

> I wouldn't like to make any claims about "best practice", for the most
> part I rely on defaults provided by more knowledgeable folks than myself.

Although trust in that approach has gotten some drawback since the
actions of RSA Inc. became public knowledge.

-- 
ir. J.C.A. Wevers
PGP/GPG public keys at http://www.xs4all.nl/~johanw/pgpkeys.html


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Re: Reusing signed user ID or attribute

[Daniel Kahn Gillmor]

On 01/19/2014 09:55 AM, Daniele Ricci wrote:
> Ok, so I have to conclude it's implementation specific?
> I'm using a custom user attribute to store something that can change
> quite often (privacy lists for a chat user). What do you suggest?

I don't know what a "privacy list for a chat user" is.  You should
probably try to document what you are trying to achieve more clearly,
and present it in a public forum where people can help you think through
possible ways to achieve it.

This thread started off by asking about user IDs or attributes, which
seems to assume that this is the only way to provide the information
you're looking for.  But an OpenPGP notation (stored within the
self-signature) could also provide that information directly.

User IDs and User Attributes are for information that you need or want
third parties to confirm and certify.  Information in an OpenPGP
notation does *not* need to be confirmed or certified by third parties.
 So if Alice wants to indicate something about her preferences about how
to use chat, she can do so in a notation subpacket within her self-sig.

does this make sense?

--dkg




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Re: Reusing signed user ID or attribute

[Hauke Laging]

Am So 19.01.2014, 15:55:51 schrieb Daniele Ricci:
> Ok, so I have to conclude it's implementation specific?
> I'm using a custom user attribute to store something that can change
> quite often (privacy lists for a chat user). What do you suggest?

My first thought is: Why should it make sense to put this data into a 
certificate?

Use a simple file with a simple signature. Let the signature expire 
every few days (or hours, whatever you need).

You may put the URL of the file into the certificate using a notation.


Hauke
-- 
Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/
http://userbase.kde.org/Concepts/OpenPGP_Help_Spread
OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5


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Re: Reusing signed user ID or attribute

[Daniele Ricci]

Ok, so I have to conclude it's implementation specific?
I'm using a custom user attribute to store something that can change
quite often (privacy lists for a chat user). What do you suggest?


On Fri, Jan 17, 2014 at 1:28 PM, Hauke Laging
 wrote:
> Am Fr 17.01.2014, 11:44:55 schrieb Daniele Ricci:
>
>> My question is the following: suppose I create a user ID or attribute.
>> I sign it with my key and that's ok.
>> One day I revoke that user ID or attribute and sign it again with a
>> certification revocation.
>>
>> A few years later, I want to restore that user ID or attribute
>> because, e.g. I restored an old e-mail address. Is it enough to sign
>> the revoked user attribute once again with a valid signature (then
>> timestamps will do the rest) or do I have to create a new user ID with
>> the same data?
>
> I am afraid that depends on the implementation. The RfC isn't clear on
> that (if I understand it correctly).
>
> It says about self-signatures (a revocation is not a self-signature in
> this sense, though):
>
> "An implementation that encounters multiple self-signatures on the same
> object may resolve the ambiguity in any way it sees fit, but it is
> RECOMMENDED that priority be given to the most recent self-signature."
>
> About revocations it says:
>
> "0x30: Certification revocation signature
>This signature revokes an earlier User ID certification signature
>(signature class 0x10 through 0x13) or direct-key signature
>(0x1F).  It should be issued by the same key that issued the
>revoked signature or an authorized revocation key.  The signature
>is computed over the same data as the certificate that it
>revokes, and should have a later creation date than that
>certificate."
>
> IIRC then GnuPG accepts a later self-signature (overriding the
> revocation). IMHO that makes most sense. As long as the mainkey isn't
> revoked or expired why shouldn't one "change one's mind"?
>
> I haven't tried now but IIRC you have to delete the revocation first
> before you can create a new signature.
>
>
> Hauke
> --
> Crypto für alle: http://www.openpgp-schulungen.de/fuer/unterstuetzer/
> http://userbase.kde.org/Concepts/OpenPGP_Help_Spread
> OpenPGP: 7D82 FB9F D25A 2CE4 5241 6C37 BF4B 8EEF 1A57 1DF5



-- 
Daniele

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gnupg binaries too big? / OpenBSD Moving Towards Signed Packages — Based On D. J. Bernstein Crypto

[Mark Schneider]

Hi,

Is there any possibility to create a minimal version of gnupg?

http://bsd.slashdot.org/story/14/01/19/0124202/openbsd-moving-towards-signed-packages-based-on-d-j-bernstein-crypto
# ---
/"It's official: 'we are moving towards signed packages 
,' says Theo de 
Raadt on the misc@ mailing list. This is shortly after a new utility, 
signify , was committed 
into the base tree. The reason a new utility had to be written in the 
first place  is that gnupg 
is too big to fit on the floppy discs, which are still a supported 
installation medium for OpenBSD. Signatures are based on the Ed25519 
 public-key signature system from D. J. 
Bernstein and co., and his public domain code once again appears 
 in the base tree 
of OpenBSD, only a few weeks after some other DJB inventions made it 
into the nearby OpenSSH 
 
as well."/



Kind regards, Mark

--
m...@it-infrastrukturen.org

http://rsync.it-infrastrukturen.org

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Re: Looking for simple wrapper for symmetric key file encryption

[Andy Ruddock]

I use ecryptfs, as packages are available for my distro (Debian) which
make it easy to install and use.

I wouldn't like to make any claims about "best practice", for the most
part I rely on defaults provided by more knowledgeable folks than myself.


Mr. Clif wrote:
> So no one got back to me.
> 
> Does anyone use symmetric file encryption? What is the best practice
> here? I heard of another solution which was to mount an encrypted
> directory with fuser to drop files into. I think I would wounder how
> safe the passphrase was for mounted filesystems, though I know of some
> techniques for protecting them.
> 
> Any pointers regarding best practices for  symmetric file encryption
> would be much appreciated.
> 
> Thanks,
> Clif
> 
> On 01/17/2014 01:15 PM, Mr. Clif wrote:
>> Greetings!
>>
>> I've been happily using pgp and gpg off and on for decades. One thing
>> I never quite figured out was what the best way to use it for
>> encrypting sensitive files on disk. After doing that one has to
>> remember to cleanup after themselves and delete all the leftover
>> plaintext versions of the file, or it kind of defeats the whole
>> purpose, and its pretty easy to make a mistake when doing it manually.
>> I always felt that GPG should help you a bit more in that regard. Now
>> I know that full disk encryption might be a way around this, but it
>> seems like overkill if you just have a couple of files to protect.
>>
>> I have searched high and low and checked out GnuPG Shell, GPA,
>> Seahorse, XAP, and some other misc wrappers but nothing seemed to fit
>> my use case. So I wrote a simple wrapper in perl. Basically it just
>> lets you toggle a file between plaintext and encrypted forms without
>> letting the plaintext version touch/remain on the disk, unless that is
>> what you want.
>>
>> #! /usr/bin/perl -U
>> #   This Perl script is a wrapper around GPG to decrypt or encrypt
>> a file.
>> #It's goal is to try to prevent plaintext from touching, or remaining
>> #on the disk, something GPG fails to do. If there is a new file
>> created
>> #It will be in the same directory as the original unless you
>> specify a new
>> #path in a second arg.
>> #
>> #By Clif 12/05/13
>> #
>>
>> # External utilities
>> $GPG   = "/usr/bin/gpg";  # GnuPG 1.4.15
>> $SHRED = "/usr/bin/shred";  # secure file deleter
>> (GNU coreutils) 8.13
>>
>> # Arguments
>> ($arg, $dest) = @ARGV;
>>
>> # Break down the pathname
>> $path = $1 if $arg  =~ /^(.*?)(\/[^\/]*)$/;
>> $file = $1 if $arg  =~ /([^\/]+)\/?$/;
>> $base = $1 if $file =~ /^(.+?)(\.[^.]*)?$/;
>> $ext  = $1 if $file =~ /\.([^. ]*)\s*$/;
>>
>> # Get destination
>> if ($dest) {
>>  $destp = 1;
>>  $dest .= "/$base" if (-d $dest);
>>  $dest =~ s/\.asc\s*$//;
>> } else { $dest = $path ? "$path/$base" : $base }
>>
>> # Is this a planetext or an encrypted file?
>>
>> if (-r $arg) {
>> if ($ext eq "asc") {# Encrypted
>> if ($destp) { system("$GPG -o $dest $arg") }
>> else{ system("$GPG -o - $arg") }
>> } else {# Plaintext
>> unlink "${dest}.asc";
>> $err = system("$GPG -o ${dest}.asc -ca --cipher-algo AES256
>> $arg");
>> if ($err) { print "ERROR = $err\n" }
>> else  { system("$SHRED -un9 $arg") }
>> }
>> } else { warn "No such file: $arg\n" }
>> # All done
>>
>>
>> Obviously it could be much more thorough but I just wanted to get the
>> idea across. I was also thinking about adding a RAM based editing
>> feature but I didn't want to reinvent the wheel if someone knows of a
>> similar project.
>>
>> Thanks for any comments you might have,
>> Clif
>>
>>
> 
> 
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Re: Looking for simple wrapper for symmetric key file encryption

[Johan Wevers]

On 19-1-2014 7:50, Mr. Clif wrote:

> Does anyone use symmetric file encryption?

Yes, but only for encrypting files for personal use. Not in
communication with others.

> What is the best practice here?

As always, that depends on your use case and threat model.

> I heard of another solution which was to mount an encrypted
> directory with fuser to drop files into.

Possible, I use TrueCryot containers for that but that's similar
(although more portable and usable on "that other  OS").

> I think I would wounder how
> safe the passphrase was for mounted filesystems,

Are you asking how long it would take to brute-force the pasword, how
difficult it is to snoop it or if there are known vulnarabilities in the
symmetric encryption used by gnupg, fuser or others?

> though I know of some techniques for protecting them.

Remember the weakest link in all encryption: https://xkcd.com/538/

-- 
ir. J.C.A. Wevers
PGP/GPG public keys at http://www.xs4all.nl/~johanw/pgpkeys.html


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