crypto: passphrase hashing with Argon2

This commit adds in the PassphraseHash function which hashes the
provided passphrase (in key form) using Argon2id. This cost parameters
for Argon2id and that salt are both fed into the function. It also
includes tests and benchmarks for the passphrase hashing.

Change-Id: I060db3e71213c756d45ce5603a0a59d3d7a1e609

1 files changed, 11 insertions, 0 deletions

diff --git a/README.md b/README.md
index e9cb5c8..79cbca8 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,15 @@ You will also want to add `$GOPATH/bin` to your `$PATH`.
 *   `make`
 *   A C compiler (`gcc` or `clang`)
 *   Go
+*   [Argon2 Passphrase Hash](https://github.com/P-H-C/phc-winner-argon2), a C
+    library which can be installed (both the header `argon2.h` and library
+    `libargon2`) by running:
+    ```bash
+    > git clone https://github.com/P-H-C/phc-winner-argon2 argon2
+    > cd argon2
+    > make
+    > sudo make install
+    ```
 
 Once this is setup, you can run `make fscrypt` to build the executable in
 `build/fscrypt`. Pass `"LDFLAGS += -static"` to `make` to get a static
@@ -84,6 +93,8 @@ dynamically linked binary by default.
 `fscrypt` has the following runtime dependencies:
 *   Kernel support for filesystem encryption (this will depend on your kernel
     configuration and specific filesystem)
+*   `libargon2` (see the above installation instructions for Argon2), unless you
+    built a static executable.
 
 Installing it just requires placing it in your path or running `make install`.
 Change `$GOBIN` to change the install location of `fscrypt`. By default,