Merge branch 'jc/push-cert'

Allow "git push" request to be signed, so that it can be verified and
audited, using the GPG signature of the person who pushed, that the
tips of branches at a public repository really point the commits
the pusher wanted to, without having to "trust" the server.

* jc/push-cert: (24 commits)
  receive-pack::hmac_sha1(): copy the entire SHA-1 hash out
  signed push: allow stale nonce in stateless mode
  signed push: teach smart-HTTP to pass "git push --signed" around
  signed push: fortify against replay attacks
  signed push: add "pushee" header to push certificate
  signed push: remove duplicated protocol info
  send-pack: send feature request on push-cert packet
  receive-pack: GPG-validate push certificates
  push: the beginning of "git push --signed"
  pack-protocol doc: typofix for PKT-LINE
  gpg-interface: move parse_signature() to where it should be
  gpg-interface: move parse_gpg_output() to where it should be
  send-pack: clarify that cmds_sent is a boolean
  send-pack: refactor inspecting and resetting status and sending commands
  send-pack: rename "new_refs" to "need_pack_data"
  receive-pack: factor out capability string generation
  send-pack: factor out capability string generation
  send-pack: always send capabilities
  send-pack: refactor decision to send update per ref
  send-pack: move REF_STATUS_REJECT_NODELETE logic a bit higher
  ...

2 files changed, 57 insertions, 5 deletions

diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index 569c48a352..462e20645f 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -212,9 +212,9 @@ out of what the server said it could do with the first 'want' line.
   want-list         =  first-want
 		       *additional-want
 
-  shallow-line      =  PKT_LINE("shallow" SP obj-id)
+  shallow-line      =  PKT-LINE("shallow" SP obj-id)
 
-  depth-request     =  PKT_LINE("deepen" SP depth)
+  depth-request     =  PKT-LINE("deepen" SP depth)
 
   first-want        =  PKT-LINE("want" SP obj-id SP capability-list LF)
   additional-want   =  PKT-LINE("want" SP obj-id LF)
@@ -465,7 +465,7 @@ contain all the objects that the server will need to complete the new
 references.
 
 ----
-  update-request    =  *shallow command-list [pack-file]
+  update-request    =  *shallow ( command-list | push-cert ) [pack-file]
 
   shallow           =  PKT-LINE("shallow" SP obj-id LF)
 
@@ -481,12 +481,27 @@ references.
   old-id            =  obj-id
   new-id            =  obj-id
 
+  push-cert         = PKT-LINE("push-cert" NUL capability-list LF)
+		      PKT-LINE("certificate version 0.1" LF)
+		      PKT-LINE("pusher" SP ident LF)
+		      PKT-LINE("pushee" SP url LF)
+		      PKT-LINE("nonce" SP nonce LF)
+		      PKT-LINE(LF)
+		      *PKT-LINE(command LF)
+		      *PKT-LINE(gpg-signature-lines LF)
+		      PKT-LINE("push-cert-end" LF)
+
   pack-file         = "PACK" 28*(OCTET)
 ----
 
 If the receiving end does not support delete-refs, the sending end MUST
 NOT ask for delete command.
 
+If the receiving end does not support push-cert, the sending end
+MUST NOT send a push-cert command.  When a push-cert command is
+sent, command-list MUST NOT be sent; the commands recorded in the
+push certificate is used instead.
+
 The pack-file MUST NOT be sent if the only command used is 'delete'.
 
 A pack-file MUST be sent if either create or update command is used,
@@ -501,6 +516,34 @@ was being processed (the obj-id is still the same as the old-id), and
 it will run any update hooks to make sure that the update is acceptable.
 If all of that is fine, the server will then update the references.
 
+Push Certificate
+----------------
+
+A push certificate begins with a set of header lines.  After the
+header and an empty line, the protocol commands follow, one per
+line.
+
+Currently, the following header fields are defined:
+
+`pusher` ident::
+	Identify the GPG key in "Human Readable Name <email@address>"
+	format.
+
+`pushee` url::
+	The repository URL (anonymized, if the URL contains
+	authentication material) the user who ran `git push`
+	intended to push into.
+
+`nonce` nonce::
+	The 'nonce' string the receiving repository asked the
+	pushing user to include in the certificate, to prevent
+	replay attacks.
+
+The GPG signature lines are a detached signature for the contents
+recorded in the push certificate before the signature block begins.
+The detached signature is used to certify that the commands were
+given by the pusher, who must be the signer.
+
 Report Status
 -------------
 
diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index e174343847..0c92deebcc 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -18,8 +18,8 @@ was sent.  Server MUST NOT ignore capabilities that client requested
 and server advertised.  As a consequence of these rules, server MUST
 NOT advertise capabilities it does not understand.
 
-The 'report-status', 'delete-refs', and 'quiet' capabilities are sent and
-recognized by the receive-pack (push to server) process.
+The 'report-status', 'delete-refs', 'quiet', and 'push-cert' capabilities
+are sent and recognized by the receive-pack (push to server) process.
 
 The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized
 by both upload-pack and receive-pack protocols.  The 'agent' capability
@@ -250,3 +250,12 @@ allow-tip-sha1-in-want
 If the upload-pack server advertises this capability, fetch-pack may
 send "want" lines with SHA-1s that exist at the server but are not
 advertised by upload-pack.
+
+push-cert=<nonce>
+-----------------
+
+The receive-pack server that advertises this capability is willing
+to accept a signed push certificate, and asks the <nonce> to be
+included in the push certificate.  A send-pack client MUST NOT
+send a push-cert packet unless the receive-pack server advertises
+this capability.