Re: [Duplicity-talk] Duplicity + asymmetric encryption

[Marko Božiković]

On 07.09.2015. 12:08, address@hidden wrote:
> On 07.09.2015 00:24, Marko Božiković wrote:
>> 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,
>>
> 
> can i see your duply conf file? obfuscate private strings in it beforehand.

Here you go.

Thank you for persevering with this :)

Just as a note (I don't remember if I've mentioned this before), I moved my
/usr/bin/gpg to /usr/bin/gpg1 and created /usr/bin/gpg symlink to gpg2.

-- 
Marko

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