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 (symmetric or asymmetric) 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. To use encryption, you run git-annex initremote in one of these ways:

  • git annex initremote newremote type=... encryption=hybrid keyid=KEYID
  • git annex initremote newremote type=... encryption=shared
  • git annex initremote newremote type=... encryption=pubkey keyid=KEYID
  • git annex initremote newremote type=... encryption=sharedpubkey keyid=KEYID

To see what encryption is used for a special remote, run git annex info $remote and look for a line like:

encryption: hybrid (to gpg keys: AEC828149D85C538 C910D9122512E3C8)

hybrid encryption keys (encryption=hybrid)

The hybrid key design allows additional encryption keys to be added on to a special remote later. Due to this flexibility, it is the default and recommended encryption scheme.

git annex initremote newremote type=... [encryption=hybrid] keyid=KEYID

The KEYID is passed to gpg to find gpg keys. Typically, you will say "keyid=2512E3C7" to use a specific gpg key. Or, you might say "" to search for matching keys.

To add a new key and allow it to access all the content that is stored in the encrypted special remote, just run git annex enableremote specifying the keyid to add:

git annex enableremote myremote keyid+=788A3F4C

You can repeat this process to add any number of gpg keys, including your own gpg keys and any public keys of others who you want to give access. Anyone with a corresponding secret key will be able to decrypt all content that is stored in the remote.

While a key can later be removed from the list, note that it will not prevent the owner of the key from accessing data on the remote (which is by design impossible to prevent, short of deleting the remote). In fact the only sound use of keyid-= is probably to replace a revoked key:

git annex enableremote myremote keyid-=2512E3C7 keyid+=788A3F4C

See also encryption design for other security risks associated with encryption.

shared encryption key (encryption=shared)

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 among every clone of the git repository.

git annex initremote newremote type=... encryption=shared

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.

regular public key encryption (encryption=pubkey)

This alternative simply encrypts the files in the special remotes to one or more public keys. The corresponding private key is needed to store anything in the remote, or access anything stored in it. It might be considered more secure due to its simplicity and since it's exactly the way everyone else uses gpg.

git annex initremote newremote type=.... encryption=pubkey keyid=KEYID

A disadvantage is that it is not easy to later add additional public keys to the special remote. While the enableremote parameters keyid+= and keyid-= can be used, they have no effect on encrypted files that are already stored in the remote.

One use for these parameters is to replace a revoked key:

git annex enableremote myremote keyid-=2512E3C7 keyid+=788A3F4C

But even in this case, since the files are not re-encrypted, the revoked key has to be kept around to be able to decrypt those files. (Of course, if the reason for revocation is that the key has been compromised, it is insecure to leave files encrypted using that old key, and the user should re-encrypt everything.)

(A cipher still needs to be generated (and is encrypted to the given key IDs). It is only used for HMAC encryption of filenames.)

regular public key encryption with shared filename encryption (encryption=sharedpubkey)

This is a variation on encryption=pubkey which lets anyone who has access to the gpg public keys store files in the special remote. But, only owners of the corresponding gpg private keys can retrieve the files from the special remote.

git annex initremote newremote type=... encryption=sharedpubkey keyid=KEYID

This might be useful if you want to let others drop off files for you in a special remote, so that only you can access them.

The filenames used on the special remote are encrypted using HMAC, which prevents the special remote from seeing the filenames. But, anyone who can clone the git repository can access the HMAC cipher; it's stored unencrypted in the git repository.

MAC algorithm

The default MAC algorithm to be applied on the filenames is HMACSHA1. A stronger one, for instance HMACSHA512, 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.