# Cipher
[](https://travis-ci.org/rubencaro/cipher)
[](https://hex.pm/packages/cipher)
Elixir crypto library to encrypt/decrypt arbitrary binaries. It uses
[Erlang Crypto](http://www.erlang.org/doc/man/crypto.html), so it's not big
deal. Mostly a collection of helpers wrapping it.
This library allows us to use a crypted key to validate signed requests, with a
cipher compatible with
[this one](https://gist.github.com/rubencaro/9545060#file-gistfile3-ex).
This way it can be used from Python, Ruby or Elixir apps.
## Use
Just add `{:cipher, github: "rubencaro/cipher"}` to your `mix.exs`.
Basically you use `encrypt/3` and `decrypt/3` to get it. You have to pass them
a key/iv pair previously generated using `generate_key/1` and `generate_iv/1`.
## Sign/validate a URL
Here you use `sign_url/3` and `validate_signed_url/3`.
`sign_url` will add a `signature` parameter to the query string. It's a crypted
hash based on the given path.
`validate_signed_url` must be given an url with the `signature` parameter on the
query string as the last one. It will pop it, and validate it corresponds with
the rest of the URL.
An example of use is [Sequeler](https://github.com/rubencaro/sequeler), and goes
like this:
* Generate the key/iv pair using `generate_key/1` and `generate_iv/1`, usually in
compile-time.
* Get the complete `path` for the request, and validate that it's signed with
the same key/iv with a call to `validate_signed_url/3`
```elixir
defmodule Sequeler.Plug do
alias Cipher, as: C
# ...
# handy to have them around
@k Application.get_env(:sequeler, :key_phrase) |> C.generate_key
@i Application.get_env(:sequeler, :iv_phrase) |> C.generate_iv
# ...
get "/query" do
path = "/query?" <> conn.query_string
valid? = C.validate_signed_url(path, @k, @i)
conn = case valid? do
true -> conn |> fetch_params |> Sequeler.Controller.query
false -> resp(conn, 401, "Unauthorized")
end
send_resp conn
end
# ...
end
```
## TODOs
* Sign POST/PUT body
* Improve README
