[PATCH v4 00/22] Signed push

The first round is found at $gmane/255520. The second round is found at $gmane/255701. The third round is found at $gmane/256464.

While signed tags and commits assert that the objects thusly signed came from you, who signed these objects, there is not a good way to assert that you wanted to have a particular object at the tip of a particular branch. My signing v2.0.1 tag only means I want to call the version v2.0.1, and it does not mean I want to push it out to my 'master' branch---it is likely that I only want it in 'maint', so the signature on the object alone is insufficient.

The only assurance to you that 'maint' points at what I wanted to place there comes from your trust on the hosting site and my authentication with it, which cannot easily audited later.

This series introduces a cryptographic assurance for ref updates done by "git push" by introducing a mechanism that allows you to sign a "push certificate" (for the lack of better name) every time you push. Think of it as working on an axis orthogonal to the traditional "signed tags".

In addition to typofixes in the log messages and comments in the earlier parts of the series since the last round, notable changes and additions in this round include the following:

 - The logic to generate "nonce" was revamped, based on HMAC-SHA1-80
   modeled after RFC 2104, suggested in $gmane/256491 [*1*].

 - Tentative "--push-cert/--no-push-cert" command line options to
   control if "receive-pack" expects/accepts a signed push is gone,
   as it is hard to arrange what goes on its command line.  It is
   now controled by receive.certnonceseed configuration variable.
   If you supply an HMAC secret to be used for generating nonce, you
   accept "git push --signed".  If you don't, you don't.

 - The last patch is new to help "stateless RPC" codepath to
   participate in the "nonce" dance.

I didn't feel bold enough to add smart-http tests to the last patch. Contributions are very much welcomed ;-)

[Reference]

*1* http://thread.gmane.org/gmane.comp.version-control.git/255520/focus=256491

Junio C Hamano (22):
  receive-pack: do not overallocate command structure
  receive-pack: parse feature request a bit earlier
  receive-pack: do not reuse old_sha1[] for other things
  receive-pack: factor out queueing of command
  send-pack: move REF_STATUS_REJECT_NODELETE logic a bit higher
  send-pack: refactor decision to send update per ref
  send-pack: always send capabilities
  send-pack: factor out capability string generation
  receive-pack: factor out capability string generation
  send-pack: rename "new_refs" to "need_pack_data"
  send-pack: refactor inspecting and resetting status and sending commands
  send-pack: clarify that cmds_sent is a boolean
  gpg-interface: move parse_gpg_output() to where it should be
  gpg-interface: move parse_signature() to where it should be
  pack-protocol doc: typofix for PKT-LINE
  push: the beginning of "git push --signed"
  receive-pack: GPG-validate push certificates
  send-pack: send feature request on push-cert packet
  signed push: remove duplicated protocol info
  signed push: add "pushee" header to push certificate
  signed push: fortify against replay attacks
  signed push: allow stale nonce in stateless mode

 Documentation/config.txt                          |   6 +
 Documentation/git-push.txt                        |   9 +-
 Documentation/git-receive-pack.txt                |  63 +++-
 Documentation/technical/pack-protocol.txt         |  49 ++-
 Documentation/technical/protocol-capabilities.txt |  13 +-
 builtin/push.c                                    |   1 +
 builtin/receive-pack.c                            | 354 +++++++++++++++++++---
 commit.c                                          |  36 ---
 gpg-interface.c                                   |  57 ++++
 gpg-interface.h                                   |  17 +-
 send-pack.c                                       | 201 +++++++++---
 send-pack.h                                       |   2 +
 t/t5534-push-signed.sh                            | 116 +++++++
 tag.c                                             |  20 --
 tag.h                                             |   1 -
 transport.c                                       |   5 +
 transport.h                                       |   5 +
 17 files changed, 799 insertions(+), 156 deletions(-)
 create mode 100755 t/t5534-push-signed.sh