%%% Copyright (c) 2014, NORDUnet A/S.
%%% See LICENSE for licensing information.

-module(x509).
-export([valid_chain_p/3, detox_precert/1]).
-include_lib("public_key/include/public_key.hrl").
-type der_encoded() :: public_key:der_encoded().

%%%%%%%%%%%%%%%%%%%%
%% @doc Verify that the leaf cert or precert has a valid chain back to
%% an acceptable root cert. Order of certificates in second argument
%% is: leaf cert in head, chain in tail. Order of first argument is
%% irrelevant.

-spec valid_chain_p([der_encoded()], [der_encoded()], integer()) -> boolean().
valid_chain_p(_, _, MaxChainLength) when MaxChainLength =< 0 ->
    false;
valid_chain_p(AcceptableRootCerts, [TopCert], MaxChainLength) ->
    case lists:member(TopCert, AcceptableRootCerts) of
        true ->                           % Top cert is part of chain.
            true;
        false ->     % Top cert might be signed by cert in truststore.
            (MaxChainLength > 1) and
                lists:any(fun(X) ->
                                  signed_by_p(TopCert, X) end,
                          AcceptableRootCerts)
    end;
valid_chain_p(AcceptableRootCerts, [BottomCert|Rest], MaxChainLength) ->
    case signed_by_p(BottomCert, hd(Rest)) of
        false -> false;
        true -> valid_chain_p(AcceptableRootCerts, Rest, MaxChainLength - 1)
    end.

-spec signed_by_p(der_encoded(), der_encoded()) -> boolean().
signed_by_p(Cert, IssuerCert) ->
    %% FIXME: Validate presence and contents (against constraints) of
    %% names (subject, subjectAltName, emailAddress) too?
    case public_key:pkix_is_issuer(Cert, IssuerCert) of
        true ->           % Cert.issuer does match IssuerCert.subject.
            public_key:pkix_verify(Cert, public_key(IssuerCert));
        false ->
            false
    end.

-spec public_key(der_encoded() | #'OTPCertificate'{}) -> public_key:public_key().
public_key(CertDer) when is_binary(CertDer) ->
    public_key(public_key:pkix_decode_cert(CertDer, otp));
public_key(#'OTPCertificate'{
              tbsCertificate =
                  #'OTPTBSCertificate'{subjectPublicKeyInfo =
                                           #'OTPSubjectPublicKeyInfo'{
                                              subjectPublicKey = Key}}}) ->
    Key.

%%%%%%%%%%%%%%%%%%%%
%% Precertificates according to draft-ietf-trans-rfc6962-bis-04.

%% Submitted precerts have a special critical poison extension -- OID
%% 1.3.6.1.4.1.11129.2.4.3, whose extnValue OCTET STRING contains
%% ASN.1 NULL data (0x05 0x00).

%% They are signed with either the CA cert that will sign the final
%% cert or Precertificate Signing Certificate directly signed by the
%% CA cert that will sign the final cert. A Precertificate Signing
%% Certificate has CA:true and Extended Key Usage: Certificate
%% Transparency, OID 1.3.6.1.4.1.11129.2.4.4.

%% A PreCert in a SignedCertificateTimestamp does _not_ contain the
%% poison extension, nor a Precertificate Signing Certificate. This
%% means that we might have to 1) remove poison extensions in leaf
%% certs, 2) remove "poisoned signatures", 3) change issuer and
%% Authority Key Identifier of leaf certs.

-spec detox_precert([#'Certificate'{}]) -> [#'Certificate'{}].
detox_precert(CertChain) ->
    CertChain.                                  % NYI