1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
|
%%% Copyright (c) 2014, NORDUnet A/S.
%%% See LICENSE for licensing information.
-module(x509).
-export([normalise_chain/2]).
-include_lib("public_key/include/public_key.hrl").
-type reason() :: {chain_too_long | root_unknown | chain_broken}.
-define(MAX_CHAIN_LENGTH, 10).
-spec normalise_chain([binary()], [binary()]) -> [binary()].
normalise_chain(AcceptableRootCerts, CertChain) ->
case valid_chain_p(AcceptableRootCerts, CertChain, ?MAX_CHAIN_LENGTH) of
{false, Reason} ->
{Reason, "invalid chain"};
{true, Root} ->
[Leaf | Chain] = CertChain,
{ok, [detox_precert(Leaf) | Chain] ++ Root}
end.
%%%%%%%%%%%%%%%%%%%%
%% @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([binary()], [binary()], integer()) ->
{false, reason()} | {true, list()}.
valid_chain_p(_, _, MaxChainLength) when MaxChainLength =< 0 ->
%% Chain too long.
{false, chain_too_long};
valid_chain_p(AcceptableRootCerts, [TopCert], MaxChainLength) ->
%% Check root of chain.
case lists:member(TopCert, AcceptableRootCerts) of
true ->
%% Top cert is part of chain.
{true, []};
false when MaxChainLength =< 1 ->
%% Chain too long.
{false, chain_too_long};
false ->
%% Top cert _might_ be signed by a cert in truststore.
case signer(TopCert, AcceptableRootCerts) of
notfound -> {false, root_unknown};
Root -> {true, [Root]}
end
end;
valid_chain_p(AcceptableRootCerts, [BottomCert|Rest], MaxChainLength) ->
case signed_by_p(BottomCert, hd(Rest)) of
false -> {false, chain_broken};
true -> valid_chain_p(AcceptableRootCerts, Rest, MaxChainLength - 1)
end.
%% @doc Return list with first
-spec signer(binary(), [binary()]) -> list().
signer(_Cert, []) ->
notfound;
signer(Cert, [H|T]) ->
case signed_by_p(Cert, H) of
true -> H;
false -> signer(Cert, T)
end.
-spec signed_by_p(binary(), binary()) -> 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(binary() | #'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
%%%%%%%%%%%%%%%%%%%%
%% Testing private functions.
-include_lib("eunit/include/eunit.hrl").
-include("x509_test.hrl").
valid_cert_test_() ->
C0 = ?C0,
C1 = ?C1,
[
%% Root not in chain but in trust store.
?_assertEqual({true, [C1]}, valid_chain_p([C1], [C0], 10)),
?_assertEqual({true, [C1]}, valid_chain_p([C1], [C0], 2)),
%% Chain too long.
?_assertMatch({false, chain_too_long}, valid_chain_p([C1], [C0], 1)),
%% Root in chain and in trust store.
?_assertEqual({true, []}, valid_chain_p([C1], [C0, C1], 2)),
%% Chain too long.
?_assertMatch({false, chain_too_long}, valid_chain_p([C1], [C0, C1], 1)),
%% Root not in trust store.
?_assertMatch({false, root_unknown}, valid_chain_p([], [C0, C1], 10)),
%% Invalid signer.
?_assertMatch({false, chain_broken}, valid_chain_p([C0], [C1, C0], 10)),
%% Selfsigned. Actually OK.
?_assertMatch({true, []}, valid_chain_p([C0], [C0], 10)),
?_assertMatch({true, []}, valid_chain_p([C0], [C0], 1)),
%% Max chain length 0 is not OK.
?_assertMatch({false, chain_too_long}, valid_chain_p([C0], [C0], 0))
].
|
