Need to restore zeroed file

David Stainton dstainton415 at gmail.com
Thu Jul 9 21:35:41 UTC 2015


Dear Roland,

I'm sorry to hear about your data loss. It is my understanding that if
you do not possess a cryptographic capability for either ReadOnly or
ReadWrite access to a file, you will NOT be able to recover it. That
is... not with some sort of cryptographic attack.

You might check if any of your Tahoe-LAFS aliases link to the file or
directory that you are trying to recover. In other words, you can
either choose to "remember" a capability inside or outside of tahoe.



On Thu, Jul 9, 2015 at 2:22 PM, Ed Kapitein <ed at kapitein.org> wrote:
> On 07/09/15 21:00, Roland Haeder wrote:
>>
>> Hello all,
>>
>> bad news: One of my files in my storage got zeroed and I don't have the
>> old (working) URI or up-to-date backup (only from 2013).
>>
>> I have currently written a brute-forcer which currently *should* test
>> all possibilities. Sure this needs massive improvement.
>>
>> So I need to know something:
>>
>> 1) Is this URL pattern valid:
>>
>>
>> http://127.0.0.1:3456/file/URI%3ACHK%3A<key1>%3A<key2>%3A3%3A10%3A<num>/@@named=/<filename>
>>
>> by:
>> <key1> = 26 Byte long character consisting of a BASE32 checksum
>> <key2> = 52 Byte long character consisting of a BASE32 checksum
>> <num>  = Random number from 0 to 99999
>> <filename> = The file's name without path
>>
>> 2) Is z_base_32_alphabet or rfc3548_alphabet taken as an alphabet?
>>
>> 3) Do I calculate this correctly?
>>
>> 26 length, each can have 32 different characters (key1)
>>
>> This means 1*32^26 =
>> 1361129467683753853853498429727072845824
>>
>> possibilities?
>>
>> And
>>
>> 1852673427797059126777135760139006525652319754650249024631321344126610074238976
>>
>> possibilities for key2?
>>
>> 3) Do I *really* have to brute-force them all to find the correct URI?
>> Or can someone (I don't like to paste brute-forcer publicly) improve the
>> search algorithm?
>>
>> Regards,
>> Roland
>>
> Well, without doing the actual math, i think our sun has died before you can
> bruteforce key1*key2*99999.
> Do you have the storage index for the lost file? that might give you a
> fighting change to get the content back.
>
> Kind regards,
> Ed
>
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