git-annex/doc/encryption.mdwn

git-annex mostly does not use encryption. Anyone with access to a git
repository can see all the filenames in it, its history, and can access
any annexed file contents.

Encryption is needed when using [[special_remotes]] like Amazon S3, where
file content is sent to an untrusted party who does not have access to the
git repository.

Such an encrypted remote uses strong GPG encryption on the contents of files,
as well as HMAC hashing of the filenames. The size of the encrypted files,
and access patterns of the data, should be the only clues to what is
stored in such a remote.

You should decide whether to use encryption with a special remote before
any data is stored in it. So, `git annex initremote` requires you
to specify "encryption=none" when first setting up a remote in order
to disable encryption.

If you want to use encryption, run `git annex initremote` with
"encryption=USERID". The value will be passed to `gpg` to find encryption keys.
Typically, you will say "encryption=2512E3C7" to use a specific gpg key.
Or, you might say "encryption=joey@kitenet.net" to search for matching keys.

The default MAC algorithm to be applied on the filenames is HMACSHA1. A
stronger one, for instance HMACSHA512, one can be chosen upon creation
of the special remote with the option `mac=HMACSHA512`. The available
MAC algorithms are HMACSHA1, HMACSHA224, HMACSHA256, HMACSHA384, and
HMACSHA512. Note that it is not possible to change algorithm for a
non-empty remote.

The [[encryption_design|design/encryption]] allows additional encryption keys
to be added on to a special remote later. Once a key is added, it is able
to access content that has already been stored in the special remote.
To add a new key, just run `git annex initremote` again, specifying the
new encryption key:

	git annex initremote myremote encryption=788A3F4C

Note that once a key has been given access to a remote, it's not
possible to revoke that access, short of deleting the remote. See
[[encryption_design|design/encryption]] for other security risks
associated with encryption.

## shared cipher mode

Alternatively, you can configure git-annex to use a shared cipher to
encrypt data stored in a remote. This shared cipher is stored,
**unencrypted** in the git repository. So it's shared amoung every
clone of the git repository. The advantage is you don't need to set up gpg
keys. The disadvantage is that this is **insecure** unless you
trust every clone of the git repository with access to the encrypted data
stored in the special remote.

To use shared encryption, specify "encryption=shared" when first setting
up a special remote.