[pass] Pass leaks password lengths through file sizes

[Von Welch]

> Do people commonly store only a password in their password store DBs?

I'd guess about half of my entries are password-only. (BTW, a common reason
for extra data is for me to store my random answers to security questions).

I agree with both Daniel's diagnosis of the problem and observation there
doesn't seem to be a simple solution. Manually adding random padding would
be one way to address this, though ideally, gnupg would have something that
would do this transparently. But looking quickly at the gnupg help and
hitting google leads me to believe it doesn't have any useful padding
mechanism built in.

Von



On Sat, May 10, 2014 at 9:10 AM, Philip Chase <philipbchase at gmail.com>wrote:

> Do people commonly store only a password in their password store DBs?
>
> I don't think a single one of my password store entries is a simple
> password. Generally they include a username or email address.  Often they
> include the security questions and answers used in password recovery
> methods.  This adds a lot of "salt" to the length.  I doubt anyone would
> get any advantage from a length-based attack against my database.
>
> Do you think my use case of extra content in each password store file is
> normal?
>
> Philip
>
>
> On Sat, May 10, 2014 at 8:47 AM, Mikhail Gusarov <dottedmag at dottedmag.net>wrote:
>
>> Adding a trailing line with a random number of space characters also can
>> help.
>>
>>
>>
>> Best regards,
>> Mikhail Gusarov.
>>
>>
>> On Sat, May 10, 2014 at 2:44 PM, Daniel Schoepe <daniel at schoepe.org>wrote:
>>
>>> Hi,
>>>
>>> one reason for using a password manager that encrypts its password
>>> store is to avoid to keep the passwords safe even if the password store
>>> itself gets into the wrong hands (e.g. if a laptop is stolen and the
>>> user didn't use hard drive encryption).
>>>
>>> However, at the moment pass seems to leak the length of the passwords
>>> through the file size of the stored passwords. As far as I can tell
>>> the file sizes vary based on the length of the GPG key that is used,
>>> but are only dependent on the password length otherwise.
>>>
>>> For example, a one-character password encrypted with a 2048 RSA key
>>> results in a file size of 324 bytes, a five-character password generates
>>> a file that is 328 bytes long, etc.. I tested this with two different
>>> 2048 bit keys.
>>>
>>> Similarly, for 4096 bit RSA keys, password file sizes start at 580 bytes
>>> and increase by one byte per password character as well.
>>>
>>> If an attacker gets his hands on a password store, this could be
>>> problematic since it decreases the search space for passwords
>>> considerably; especially if they have some offline method of
>>> bruteforcing passwords (e.g. if they obtained the hash of a user's
>>> password from some database).
>>>
>>> I think this is an issue and should be fixed, even though all the fixes
>>> I can see would detract from the simplicity of the current
>>> implementation.
>>>
>>> One way to remedy this is the following: When adding a new password one
>>> could generate a random number of bytes and append that, along with
>>> information on how many junk bytes were added, to the entry and discard
>>> them when reading the password. This has the disadvantage of the files
>>> no longer being easily readable/usable without pass.
>>>
>>> I'd like to know if others also think that this is a security issue and
>>> if there are better ways of fixing it.
>>>
>>> Cheers,
>>> Daniel
>>> _______________________________________________
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>>> Password-Store at lists.zx2c4.com
>>> http://lists.zx2c4.com/mailman/listinfo/password-store
>>>
>>
>>
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>>
>>
>
>
> --
> Philip Chase * 352-575-0705 * Gainesville, FL
>
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