Initial Documentation for fscrypt

This commit includes the Apache 2.0 License and a README with
documentation on how to checkout the code, some context about Linux
filesystem encryption, and documentation stubs for fscrypt and
fscryptctl. Also adds in a simple .gitignore so we don't commit build
files.

Change-Id: I99d5f936c9d65516119dd58c81cfa95c1e6243c1

1 files changed, 89 insertions, 6 deletions

diff --git a/README.md b/README.md
index cadd37f..c6bfa6a 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,91 @@
-# FSCrypt
+# fscrypt
 
-An tool for uniform management of encrypted disks/directories;
-[written in go](https://golang.org/).
+<!-- TODO: Insert link to fscryptctl when it is released -->
+`fscrypt` is a high-level tool [written in Go](https://golang.org) for the
+management of [Linux filesystem encryption](https://lwn.net/Articles/639427).
+This tool manages metadata, key generation, key wrapping, PAM integration, and
+provides a uniform interface for creating and modifying encrypted directories.
+For a small low-level tool that directly manipulates keys and policies, see
+`fscryptctl`.
 
-FSCrypt is a tool for unified management of disk encryption. It manages
-metadata, key generation, key wrapping, PAM integration, and provides a uniform
-interface for creating and modifying encrypted directories and devices.
+To use `fscrypt`, you must have a filesystem with encryption enabled and a
+kernel that supports reading/writing from that filesystem. Currently,
+[ext4](https://en.wikipedia.org/wiki/Ext4),
+[F2FS](https://en.wikipedia.org/wiki/F2FS), and
+[UBIFS](https://en.wikipedia.org/wiki/UBIFS) support Linux filesystem
+encryption. Ext4 has supported Linux filesystem encryption
+[since v4.1](https://lwn.net/Articles/639427), F2FS
+[added support in v4.2](https://lwn.net/Articles/649652), and UBIFS
+[added support in v4.10](https://lwn.net/Articles/707900). Note that only
+certain configurations of the Linux kernel enable encryption, and other
+filesystems may add support for encryption.
+
+Most of the testing for `fscrypt` has been done with ext4 filesystems. However,
+the kernel uses a common userspace interface, so this tool should work with all
+existing and future filesystems which support for encryption. If there is a
+problem using `fscrypt` with other filesystems, please open an issue.
+
+### Other encryption solutions
+
+It is important to distinguish Linux filesystem encryption from two other
+encryption solutions: [eCryptfs](https://en.wikipedia.org/wiki/ECryptfs) and
+[dm-crypt](https://en.wikipedia.org/wiki/Dm-crypt).
+
+Currently, dm-crypt encrypts an entire block device with a single master key. If
+you do not need the fine-grained controls of `fscrypt` or want to fully encrypt
+your filesystem metadata, dm-crypt could be a simpler choice.
+
+On the other hand, eCryptfs is another form of filesystem encryption on Linux;
+it encrypts a filesystem directory with some key or passphrase. eCryptfs sits on
+top of an existing filesystem. This make eCryptfs an alternative choice if your
+filesystem or kernel does not support Linux filesystem encryption or you do not
+want to modify your existing filesystem.
+
+Also note that `fscrypt` does not support or setup either eCryptfs or dm-crypt.
+For these tools, use
+[ecryptfs-utils](https://packages.debian.org/source/jessie/ecryptfs-utils) for
+eCryptfs or [cryptsetup](https://linux.die.net/man/8/cryptsetup) for dm-crypt.
+
+## Features
+
+`fscrypt` is intended to improve upon the work in
+[e4crypt](http://man7.org/linux/man-pages/man8/e4crypt.8.html) by providing a
+more managed environment and handling more functionality in the
+background. `fscrypt` has a [design document](https://goo.gl/55cCrI) that
+discusses many of the higher level design choices that were made.
+
+Specifically, `fscrypt` contains the following functionality:
+*   TODO
+
+## Building
+
+<!-- TODO: Change git clone URL before public release -->
+Get the source by running `git clone [REDACTED] fscrypt`.
+You need to [setup your `GOPATH`](https://golang.org/doc/code.html#GOPATH) and
+clone the repository into `$GOPATH/src/fscrypt`.
+
+## Running and Installing
+
+TODO
+
+## Example Usage
+
+TODO
+
+## Contributing
+
+TODO
+
+## Known Issues
+
+None so far!
+
+## License
+
+Copyright 2017 Google Inc.
+
+Author: Joe Richey <joerichey@google.com>
+
+Distributed under the
+[Apache 2.0 License](https://www.apache.org/licenses/LICENSE-2.0); see the
+`LICENSE` file for more information.