Re: [Duplicity-talk] Duplicity + asymmetric encryption

[Marko Božiković]

On 03.08.2015. 3:31, address@hidden wrote:
> 
> 
> On August 2, 2015 11:41:31 PM GMT+02:00, "Marko Božiković" <address@hidden> 
> wrote:
>> Hi all,
>>
>> I've started playing with Duplicity for my cloud backup needs and I
>> have a few
>> questions regarding asymmetric encryption with gpg. Apologies for a
>> long mail,
>> but I'm confused by Duplicity's behaviour.
>>
>> I'm using Debian Jessie, duply 1.9.2, duplicity 0.7.3 and gpg 2.1.6
>> (these are
>> installed from testing/experimental repos)
>>
>> I've created a symbolic link gpg->gpg2 in order to force duplicity to
>> use gpg2.
>>
>> I have a gpg2 keyring setup with a master 4096 bit key, three 2048 bit
>> subkeys
>> (for signing, encryption and authentication) for everyday use that are
>> stored
>> on a smart card and a newly created 2048 bit (S, E) subkey for
>> duplicity backup.
>>
>> I keep my secret master key offline. The keyring on my laptop only
>> contains
>> the master public key and stubs for secret subkeys that live on the
>> smartcard.
>> The keyring on my backup machine only contains the public master key
>> and the
>> duplicity backup subkey.
>>
>> Here are the relevant bits from my duply config (I've replaced my
>> backup key's
>> fingerprint with YYYYYYYY:
>>
>> GPG_KEY='YYYYYYYY'
>> GPG_OPTS='--pinentry-mode loopback'
>> VOLSIZE=250
>> DUPL_PARAMS="$DUPL_PARAMS --volsize $VOLSIZE "
>> DUPL_PARAMS="$DUPL_PARAMS --file-prefix-archive=backup-data-
>> --file-prefix-manifest=includes- --file-prefix-signature=signatures-"
>>
>> Gpg 2.1 always uses gpg-agent for secret key access and it doesn't set
>> GPG_AGENT_INFO env. variable. This is the output I get when I run duply
>> with
>> no GPG_AGENT_INFO set (YYYYYYYY is my backup key's fingerprint and
>> XXXXXXXX is
>> my master key fingerprint)
>>
>> -------------------------------
>> -- BEGIN no GPG_AGENT_INFO set
>> -------------------------------
>> Start duply v1.9.2, time is 2015-08-02 22:02:48.
>> Using profile '/home/bozho/.duply/photo'.
>> Using installed duplicity version 0.7.03, python 2.7.10, gpg 2.1.6
>> (Home:
>> ~/.gnupg), awk 'mawk 1.3.3 Nov 1996, Copyright (C) Michael D. Brennan',
>> grep
>> '(GNU grep) 2.20', bash '4.3.30(1)-release (x86_64-pc-linux-gnu)'.
>> Autoset found secret key of first GPG_KEY entry 'YYYYYYYY' for signing.
>> Cannot use gpg-agent. GPG_AGENT_INFO not set.
>> Checking TEMP_DIR '/tmp' is a folder (OK)
>> Checking TEMP_DIR '/tmp' is writable (OK)
>> Enter passphrase: <MY SECRET KEY PASSWORD>
>> Test - Encrypt to 'YYYYYYYY' & Sign with 'YYYYYYYY' (OK)
>> Test - Decrypt (OK)
>> Test - Compare (OK)
>> Cleanup - Delete '/tmp/duply.1629.1438549369_*'(OK)
>> Export SEC key 'YYYYYYYY' (FAILED)
>>
>> WARNING:
>>
>> Backup failed.
>> gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No
>> passphrase
>> given - skipped
>>
>> Export SEC key 'YYYYYYYY' (FAILED)
>>
>> WARNING:
>>
>> Backup failed.
>> gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No
>> passphrase
>> given - skipped
>>
>>
>> --- Start running command PRE at 22:03:14.018 ---
>> Skipping n/a script '/home/bozho/.duply/photo/pre'.
>> --- Finished state OK at 22:03:14.122 - Runtime 00:00:00.103 ---
>>
>> --- Start running command BKP at 22:03:14.135 ---
>> Reading globbing filelist /home/bozho/.duply/photo/exclude
>> Local and Remote metadata are synchronized, no sync needed.
>> Last full backup date: none
>> GnuPG passphrase: <ANY PASSPHRASE>
>> GnuPG passphrase for signing key: <MY SECRET KEY PASSWORD>
>> No signatures found, switching to full backup.
>> -------------------------------
>> -- END no GPG_AGENT_INFO set
>> -------------------------------
>>
>>
>> Note that I get asked a passphrase three times:
>>
>> - "Enter passphrase", which requires my secret backup subkey password -
>> why is
>> that needed here?
>>
>> - "GnuPG passphrase:", which can be any password - I'm guessing that's
>> used as
>> the session key that actually encrypts the data and then gets encrypted
>> by my
>> public subkey. Why is this necessary? In OpenPGP, the session key
>> can/should
>> be a long random key - the recipient doesn't need to know it.
>>
>> - "GnuPG passphrase for signing key" - ok, this one is for signing,
>> since it's
>> enabled and I'm using the same key.
>>
>>
>>
>> Now, if I restart gpg-agent in order to reset its caching and actually
>> export
>> GPG_AGENT_INFO, I get a slightly different output:
>>
>> -------------------------------
>> -- BEGIN GPG_AGENT_INFO set
>> -------------------------------
>> Start duply v1.9.2, time is 2015-08-02 22:12:42.
>> Using profile '/home/bozho/.duply/photo'.
>> Using installed duplicity version 0.7.03, python 2.7.10, gpg 2.1.6
>> (Home:
>> ~/.gnupg), awk 'mawk 1.3.3 Nov 1996, Copyright(C) Michael D. Brennan',
>> grep
>> '(GNU grep) 2.20', bash '4.3.30(1)-release (x86_64-pc-linux-gnu)'.
>> Autoset found secret key of first GPG_KEY entry 'YYYYYYYY' for signing.
>> Autoenable use of gpg-agent. GPG_PW or GPG_PW_SIGN (enc != sign key)
>> not set.
>> Checking TEMP_DIR '/tmp' is a folder (OK)
>> Checking TEMP_DIR '/tmp' is writable (OK)
>> Enter passphrase: <MY SECRET KEY PASSWORD>
>> Test - Encrypt to 'YYYYYYYY' & Sign with 'YYYYYYYY' (OK)
>> Test - Decrypt (OK)
>> Test - Compare (OK)
>> Cleanup - Delete '/tmp/duply.4740.1438549962_*'(OK)
>> Export SEC key 'YYYYYYYY' (FAILED)
>>
>> WARNING:
>>
>> Backup failed.
>> gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No
>> passphrase
>> given - skipped
>>
>> Export SEC key 'YYYYYYYY' (FAILED)
>>
>> WARNING:
>>
>> Backup failed.
>> gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No
>> passphrase
>> given - skipped
>>
>>
>> --- Start running command PRE at 22:13:22.870 ---
>> Skipping n/a script '/home/bozho/.duply/photo/pre'.
>> --- Finished state OK at 22:13:22.956 - Runtime 00:00:00.085 ---
>>
>> --- Start running command BKP at 22:13:22.966 ---
>> Reading globbing filelist /home/bozho/.duply/photo/exclude
>> Local and Remote metadata are synchronized, no sync needed.
>> Last full backup date: none
>> No signatures found, switching to full backup.
>> -------------------------------
>> -- END GPG_AGENT_INFO set
>> -------------------------------
>>
>> Notice that I get asked for a password only once, at the beginning
>> ("Enter
>> passphrase") Why is that, and is the session key being randomly
>> generated in
>> this case or is my secret subkey password used as a session key (this
>> is a bad
>> idea)
>>
>> Thank you,
> 
> 
> probably 
>  https://sourceforge.net/p/ftplicity/feature-requests/36/
> 
> try setting --use-agent manually in conf.
> 
> ..ede/duply.net
> 


Hi,

Sorry for a late reply.

I tried using your suggestion and added --use-agent to DUPL_PARAMS, but it
didn't help.

I've tried with and without setting GPG_AGENT_INFO variable, I get the same
output after being asked for the key password:



Start duply v1.9.2, time is 2015-09-05 22:45:50.
Using profile '/home/bozho/.duply/photo'.
Using installed duplicity version 0.7.03, python 2.7.10, gpg 2.1.6 (Home:
~/.gnupg), awk 'mawk 1.3.3 Nov 1996, Copyright (C) Michael D. Brennan', grep
'(GNU grep) 2.21', bash '4.3.39(1)-release (x86_64-pc-linux-gnu)'.
Autoset found secret key of first GPG_KEY entry 'YYYYYYYY' for signing.
Autoenable use of gpg-agent. GPG_PW or GPG_PW_SIGN (enc != sign key) not set.
Checking TEMP_DIR '/tmp' is a folder (OK)
Checking TEMP_DIR '/tmp' is writable (OK)
Test - Encrypt to 'YYYYYYYY' & Sign with 'YYYYYYYY' (OK)
Test - Decrypt (OK)
Test - Compare (OK)
Cleanup - Delete '/tmp/duply.3034.1441489550_*'(OK)
Export SEC key 'YYYYYYYY' (FAILED)

WARNING:

Backup failed.
gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No passphrase
given - skipped

Export SEC key 'YYYYYYYY' (FAILED)

WARNING:

Backup failed.
gpg: key XXXXXXXX/YYYYYYYY: error receiving key from agent: No passphrase
given - skipped


--- Start running command PRE at 22:45:54.331 ---
Skipping n/a script '/home/bozho/.duply/photo/pre'.
--- Finished state OK at 22:45:54.410 - Runtime 00:00:00.079 ---

--- Start running command BKP at 22:45:54.419 ---
Reading globbing filelist /home/bozho/.duply/photo/exclude
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: none
No signatures found, switching to full backup.




However, the backup seems to proceed normally...

Thank you,
-- 
Marko