git-crypt/README

ABOUT GIT-CRYPT

git-crypt enables transparent encryption and decryption of files in a
git repository.  Files which you choose to protect are encrypted when
committed, and decrypted when checked out.  git-crypt lets you freely
share a repository containing a mix of public and private content.
git-crypt gracefully degrades, so developers without the secret key can
still clone and commit to a repository with encrypted files.  This lets
you store your secret material (such as keys or passwords) in the same
repository as your code, without requiring you to lock down your entire
repository.

git-crypt was written by Andrew Ayer <agwa at andrewayer dot name>.
For more information, see <http://www.agwa.name/projects/git-crypt>.


BUILDING GIT-CRYPT

See the INSTALL file.


USING GIT-CRYPT

Generate a secret key:

	$ git-crypt keygen /path/to/keyfile

Configure a repository to use encryption:

	$ cd repo
	$ git-crypt init /path/to/keyfile

Specify files to encrypt by creating a .gitattributes file:

	secretfile filter=git-crypt diff=git-crypt
	*.key filter=git-crypt diff=git-crypt

Like a .gitignore file, it can match wildcards and should be checked
into the repository.  Make sure you don't accidentally encrypt the
.gitattributes file itself!

Cloning a repository with encrypted files:

	$ git clone /path/to/repo
	$ cd repo
	$ git-crypt init /path/to/keyfile

That's all you need to do - after running git-crypt init, you can use
git normally - encryption and decryption happen transparently.


CURRENT STATUS

The latest version of git-crypt is 0.3, released on 2013-04-05.
git-crypt aims to be bug-free and reliable, meaning it shouldn't
crash, malfunction, or expose your confidential data.  However,
it has not yet reached maturity, meaning it is not as documented,
featureful, or easy-to-use as it should be.  Additionally, there may be
backwards-incompatible changes introduced before version 1.0.

Development on git-crypt is currently focused on improving the user
experience, especially around setting up repositories.  There are also
plans to add additional key management schemes, such as passphrase-derived
keys and keys encrypted with PGP.


SECURITY

git-crypt is more secure that other transparent git encryption systems.
git-crypt encrypts files using AES-256 in CTR mode with a synthetic IV
derived from the SHA-1 HMAC of the file.  This is provably semantically
secure under deterministic chosen-plaintext attack.  That means that
although the encryption is deterministic (which is required so git can
distinguish when a file has and hasn't changed), it leaks no information
beyond whether two files are identical or not.  Other proposals for
transparent git encryption use ECB or CBC with a fixed IV.  These systems
are not semantically secure and leak information.

The AES key is stored unencrypted on disk.  The user is responsible for
protecting it and ensuring it's safely distributed only to authorized
people.  A future version of git-crypt may support encrypting the key
with a passphrase.


LIMITATIONS

git-crypt is not designed to encrypt an entire repository.  Not only does
that defeat the aim of git-crypt, which is the ability to selectively
encrypt files and share the repository with less-trusted developers, there
are probably better, more efficient ways to encrypt an entire repository,
such as by storing it on an encrypted filesystem.  Also note that
git-crypt is somewhat of an abuse of git's smudge, clean, and textconv
features.  Junio Hamano, git's maintainer, has said not to do this
<http://thread.gmane.org/gmane.comp.version-control.git/113124/focus=113221>,
though his main objection ("making a pair of similar 'smudged' contents
totally dissimilar in their 'clean' counterparts.") does not apply here
since git-crypt uses deterministic encryption.

git-crypt does not itself provide any authentication.  It assumes that
either the master copy of your repository is stored securely, or that
you are using git's existing facilities to ensure integrity (signed tags,
remembering commit hashes, etc.).