defmodule Plug.Crypto.MessageVerifier do
@moduledoc """
`MessageVerifier` makes it easy to generate and verify messages
which are signed to prevent tampering.
For example, the cookie store uses this verifier to send data
to the client. The data can be read by the client, but cannot be
tampered with.
"""
@doc """
Decodes and verifies the encoded binary was not tampared with.
"""
def verify(binary, secret) when is_binary(binary) and is_binary(secret) do
case String.split(binary, "--") do
[content, digest] when content != "" and digest != "" ->
if Plug.Crypto.secure_compare(digest(secret, content), digest) do
Base.decode64(content)
else
:error
end
_ ->
:error
end
end
@doc """
Signs a binary according to the given secret.
"""
def sign(binary, secret) when is_binary(binary) and is_binary(secret) do
encoded = Base.encode64(binary)
encoded <> "--" <> digest(secret, encoded)
end
defp digest(secret, data) do
:crypto.hmac(:sha, secret, data) |> Base.encode64
end
end