eae

= eae
Equim <https://github.com/Equim-chan[@Equim-chan]>
:tip-caption: :bulb:

image:https://img.shields.io/github/release/Equim-chan/eae.svg[Release, link=https://github.com/Equim-chan/eae/releases/latest]
image:https://img.shields.io/github/license/Equim-chan/eae.svg[License, link=https://github.com/Equim-chan/eae/blob/master/LICENSE]

eae is a tiny CLI tool that helps encrypt/decrypt a single file using AEAD ciphers. The key is derived using https://www.tarsnap.com/scrypt/scrypt.pdf[scrypt]. AES256GCM and ChaCha20Poly1305 are supported.

TIP: For further documents, please refer to eae(1).

== Install
You can view the https://github.com/Equim-chan/eae/releases[release] page for handy prebuilt binaries.

== Build
To build eae, https://github.com/golang/dep[dep] and https://github.com/josephspurrier/goversioninfo[goversioninfo] are required. If you want to build the manpage, you need http://asciidoctor.org/[asciidoctor] too.

[source,bash]
----
$ git clone https://github.com/Equim-chan/eae.git $GOPATH/src/ekyu.moe/eae
$ cd $GOPATH/src/ekyu.moe/eae
$ make
$ make install
$ $GOPATH/bin/eae
----

== Details
=== File format
The following values are all in little endian.

image::https://raw.github.com/Equim-chan/eae/master/file_format.png[figure]

=== Nonce counter
First, we generate a 12-byte cryptographically strong pseudo-random slice as `nonceSeed`, and a slice `counter` of 12-byte zero. When a new chunk is to be processed, `nonce` will be `nonceSeed` XOR `counter`, and then counter will increases itself by 0x1 in little endian. This is implemented in https://github.com/Equim-chan/eae/blob/master/lib/aeadstream/aeadstream.go[lib/aeadstream/aeadstream.go].

Technically, when chunk size is 256KiB (as in eae), and nonce size is 12 bytes, one single _key_(not _passphrase_) can be used to process at most 2^54 EiB of data.

== License
https://github.com/Equim-chan/eae/blob/master/LICENSE[Apache-2.0]