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0.4.1
Compose web applications with functions
Security advisory:
This version has known vulnerabilities.
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lib/plug/crypto/message_verifier.ex
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.
"""
@delimiter "##"
@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 split(binary) do
[content, digest] when content != "" and digest != "" ->
if Plug.Crypto.secure_compare(digest(secret, content), digest) do
decode(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.url_encode64(binary)
encoded <> @delimiter <> digest(secret, encoded)
end
defp digest(secret, data) do
:crypto.hmac(:sha, secret, data) |> Base.url_encode64
end
# TODO: Remove after backwards compatibility period
defp split(binary) do
case String.split(binary, @delimiter) do
[_, _] = both -> both
_ -> String.split(binary, "--")
end
end
# TODO: Remove after backwards compatibility period
defp decode(content) do
case Base.url_decode64(content) do
{:ok, binary} -> {:ok, binary}
:error -> Base.decode64(content)
end
end
end