Timestamps git commits, so that opentimestamps proofs can be generated.

Timestamp .ots files attesting existence of commits are stored in refs/timestamps/commits (this ref points to a commit object whose associated tree references the blobs containing .ots files).

Pending timestamps (unsubmitted and/or not yet included in bitcoin blockchain) are listed in refs/timestamps/pending. The ref points to a binary blob which can be read using:

git cat-file blob refs/timestamps/pending | xxd -c 53 -g 21

The first byte is either 0x00 or 0x01 depending on whether the digest is unsubmitted, or the timestamp is pending.

Calendar URLs are contained in refs/timestamps/calendars. The ref points to a blob which can be read using:

git cat-file blob refs/timestamps/calendars

Commit objects which have been timestamped will have a "note" listing the block height which attests to their existence. See git-notes for more details. Timestamped commits can be searched using:

git log --grep "bitcoin attests existence as of height" --grep "pending timestamp submitted on"

To create a merkle root digest for tree of <COMMIT-ID>, run:

tstamp -i <COMMIT-ID>

To set calendar the URLs:

tstamp -c https://alice.btc.calendar.opentimestamps.org \
-c https://bob.btc.calendar.opentimestamps.org \
-c https://btc.calendar.catallaxy.com \
-c https://finney.calendar.eternitywall.com \

To submit unsubmitted digests, and upgrade any pending timestamps which are ready:

tstamp -u

With -d flag, delete any unsubmitted digests instead of submitting them:

tstamp -u -d

Suppose that <COMMIT-ID> has been timestamped in the above fashion, and file.txt is a file in the tree referenced by the commit. Generate an .ots proof for file.txt:

tstamp -i <COMMIT-ID> -f file.txt

The resulting file.txt_<GIT-BLOB-ID>.ots file can be verified on opentimestamps using the version of file.txt corresponding to <GIT-BLOB-ID>. The file data can be output using, e.g.,

git cat-file blob <GIT-BLOB-ID> > file.txt_<GIT-BLOB-ID>

As a special case, one can also generate a proof for the commit data:

tstamp -i <COMMIT-ID> --commit-proof

The resulting file <COMMIT-ID>.ots is a timestamp for the data returned by:

git cat-file commit <COMMIT-ID>

See the example for an .ots file for init commit in this repository.