# git-remote-gcrypt
# Copyright 2013  by Ulrik Sverdrup
# License: GPLv2 or any later version, see http://www.gnu.org/licenses/
# Use GnuPG to use encrypted git remotes

WARNING: Repository format MAY STILL change, incompatibly

INTRODUCTION

Install as `git-remote-gcrypt` in $PATH

Supports local, ssh:// and sftp:// remotes at the moment,
as well as the special gitception://<giturl> remote type::

    git remote add gcryptrepo gcrypt::ssh://hostname.com:MyNewRepo
     ( or maybe:
       git remote add gcryptrepo gcrypt::gitception://git://host.com/repo.git
     )
    git push --all gcryptrepo

DESIGN GOALS

 + Confidential, authenticated git storage and collaboration on any
   untrusted file host or service. The only information we (by necessity)
   leak is the approximate size and timing of updates.
   PLEASE help me evaluate how well we meet this design goal!

CONFIGURATION

 + You must set up a small gpg keyring for the repository::

     gpg --export KEYID1 > <path-to-keyring>
     git config gcrypt.keyring <path-to-keyring>

   New repositories will be set up to allow access for the keys in
   `gcrypt.keyring`. The keyring is used to verify the authenticity of the
   repository when it is read or written to.

 + NOTE: We use the user's gnupg configuration for `cipher-algo` and so on!
         Configure your gnupg to use strong crypto -- see `man gpg`.


REPOSITORY FORMAT

 + The manifest is signed+encrypted using `gpg -se` (with hidden recipients)
   and stored on the remote.
 + The manifest contains the list of branches and packfiles.

    $ cd MyCryptedRemote
    $ ls 
    -rw-- 11K 00ef27cc2c5b76365e1a46479ed7429e16572c543cdff0a8bf745c7c
    -rw-- 41K b934d8d6c0f48e71b9d7a4d5ea56f024a9bed4f6f2c6f8e688695bee
    -rw-- 577 manifest
    
    $ gpg -d manifest
    T+pCUr/1FxbBC93ABIiIgG36EgqaxvgdNYjdmRSueGkgGETc4Qs7di+/yIsq2R5GysiqFaR0 \
    bGSWf9omsoAH84hmED/kR/ZQiOGT/vg2Pg7CGI0xzdlW9GQjeFBAo4vsDDDBxrn5L7F9E532 \
    LOnnPLSIZD7BpmyY/oZiXoP5Vlw=
    b4a4a39365d19282810c19d0f3f24d04dd2d179f refs/tags/something
    1d323ddadf4cf1d80fced447e637ab3766b168b7 refs/heads/master
    pack :SHA224:00ef27cc2c5b76365e1a46479ed7429e16572c543cdff0a8bf745c7c
    pack :SHA224:b934d8d6c0f48e71b9d7a4d5ea56f024a9bed4f6f2c6f8e688695bee


 + Protocol sketch

   EncSign(X) is sign+encrypting to a PGP key holder
   Encrypt(K,X) is symmetric encryption

   K: master key, generated once, 128 bytes
   B: branch list
   L: list of packfiles and hashes
   
   Store Manifest as EncSign(K || B || L)
   Each packfile P is stored as P' = Encrypt(K,P) and named SHA224(P')
   L is the list of names of P'.


   To read the repository

   decrypt+verify Manifest using private key -> (K, B, L)
   for each packfile P' in L:
       verify  P' matches its hash
       decrypt P' using K -> P -> open P with git

   Only packs mentioned in L are downloaded.