Created
May 12, 2023 04:48
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defmodule CertChecker do | |
alias X509.Certificate, as: Cert | |
def check_file(file) do | |
[cert | chain] = read_pem_file(file) | |
check_certs(cert, chain) | |
end | |
def check_certs(cert, chain) do | |
cert_map = chain |> map_by_subject() | |
ca_map = cacerts() |> map_by_subject() | |
with {:ok, path} <- path_to_ca(cert, cert_map, ca_map) do | |
[root_der | _] = path_der = [cert | path] |> Enum.reverse() |> Enum.map(&Cert.to_der/1) | |
:public_key.pkix_path_validation(root_der, path_der, verify_fun: {&verify/3, nil}) | |
end | |
end | |
defp read_pem_file(file) do | |
file | |
|> File.read!() | |
|> :public_key.pem_decode() | |
|> Enum.map(fn {:Certificate, der, :not_encrypted} -> Cert.from_der!(der) end) | |
end | |
defp cacerts do | |
:certifi.cacerts() | |
|> Enum.map(&X509.Certificate.from_der!/1) | |
end | |
defp map_by_subject(certs) do | |
Map.new(certs, &{Cert.subject(&1), &1}) | |
end | |
defp path_to_ca(cert, cert_map, ca_map) do | |
issuer = Cert.issuer(cert) | |
cond do | |
ca = Map.get(ca_map, issuer) -> | |
{:ok, [ca]} | |
next_cert = Map.get(cert_map, issuer) -> | |
with {:ok, path} <- path_to_ca(next_cert, cert_map, ca_map) do | |
{:ok, [next_cert | path]} | |
end | |
true -> | |
{:error, :no_path_to_ca} | |
end | |
end | |
def verify_debug(cert, msg, state) do | |
{common_name(cert), msg} |> IO.inspect() | |
verify(cert, msg, state) | |
end | |
def verify(_, {:bad_cert, _} = reason, _), do: {:fail, reason} | |
def verify(_, {:extension, _}, state), do: {:unknown, state} | |
def verify(_, :valid, state), do: {:valid, state} | |
def verify(_, :valid_peer, state), do: {:valid, state} | |
defp common_name(cert) do | |
cert | |
|> X509.Certificate.subject() | |
|> X509.RDNSequence.get_attr("commonName") | |
end | |
end |
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