Implement cert chain validation.validate_certchain

NOTE0: Presence of and constraints on names are not being validated.
NOTE1: Validation not invoked at submission yet.

3 files changed, 240 insertions, 0 deletions

diff --git a/src/x509.erl b/src/x509.erl
new file mode 100644
index 0000000..c6aa705
--- /dev/null
+++ b/src/x509.erl
@@ -0,0 +1,76 @@
+%%% 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
diff --git a/src/x509_test.erl b/src/x509_test.erl
new file mode 100644
index 0000000..c06bc8b
--- /dev/null
+++ b/src/x509_test.erl
@@ -0,0 +1,53 @@
+-module(x509_test).
+
+-include_lib("eunit/include/eunit.hrl").
+
+%% remove_poison_test_() ->
+%%     {foreach,
+%%      fun() -> {ok, Pem} = file:read(File), Pem end,
+%%      fun(_) -> ok end,
+%%      fun(ChainPem) ->
+%%              [CleanPem = x509:detox_precert(ChainPem),
+%%               ?_assertEqual(CleanPem, )]
+%%                  }.
+
+-include("x509_test.hrl").
+valid_cert_test_() ->
+    C0 = ?C0,
+    C1 = ?C1,
+    [
+     %% Root not in chain but in trust store.
+     ?_assertMatch(true, x509:valid_chain_p([C1], [C0], 10)),
+     ?_assertMatch(true, x509:valid_chain_p([C1], [C0], 2)),
+     %% Chain too long.
+     ?_assertMatch(false, x509:valid_chain_p([C1], [C0], 1)),
+     %% Root in chain and in trust store.
+     ?_assertMatch(true, x509:valid_chain_p([C1], [C0, C1], 2)),
+     %% Chain too long.
+     ?_assertMatch(false, x509:valid_chain_p([C1], [C0, C1], 1)),
+     %% Root not in trust store.
+     ?_assertMatch(false, x509:valid_chain_p([], [C0, C1], 10)),
+     %% Invalid signer.
+     ?_assertMatch(false, x509:valid_chain_p([C0], [C0, C1], 10)),
+     ?_assertMatch(false, x509:valid_chain_p([C0], [C1], 10)),
+     %% Selfsigned. Actually OK.
+     ?_assertMatch(true, x509:valid_chain_p([C0], [C0], 10)),
+     ?_assertMatch(true, x509:valid_chain_p([C0], [C0], 1)),
+     %% Max chain length 0 is not OK.
+     ?_assertMatch(false, x509:valid_chain_p([C0], [C0], 0))
+     %% ?_assertMatch(true, x509:valid_chain_p(certs_from_file(certfile(cabundle)),
+     %%                                        certs_from_file(certfile(0)))),
+     %% ?_assertEqual(false, x509:valid_chain_p(certs_from_file(certfile(cabundle)),
+     %%                                         certs_from_file(certfile(1))))
+    ].
+
+certfile(cabundle) ->
+    "../certs/testcerts/acceptable_roots.pem";
+certfile(0) ->
+    "../certs/testcerts/cert1.txt";
+certfile(1) ->
+    "../certs/testcerts/cert2.txt".
+
+certs_from_file(Fname) ->
+    {ok, Pems}  = file:read_file(Fname),
+    public_key:pem_decode(Pems).
diff --git a/src/x509_test.hrl b/src/x509_test.hrl
new file mode 100644
index 0000000..93803a2
--- /dev/null
+++ b/src/x509_test.hrl
@@ -0,0 +1,111 @@
+%% C1 signs C0
+
+-define(C0,
+  <<48,130,5,5,48,130,3,237,160,3,2,1,2,2,17,0,223,204,174,11,223,131,19,38,89,
+  67,221,26,255,213,96,72,48,13,6,9,42,134,72,134,247,13,1,1,5,5,0,48,54,49,11,
+  48,9,6,3,85,4,6,19,2,78,76,49,15,48,13,6,3,85,4,10,19,6,84,69,82,69,78,65,49,
+  22,48,20,6,3,85,4,3,19,13,84,69,82,69,78,65,32,83,83,76,32,67,65,48,30,23,13,
+  49,52,48,55,48,51,48,48,48,48,48,48,90,23,13,49,55,48,55,48,50,50,51,53,57,
+  53,57,90,48,129,188,49,11,48,9,6,3,85,4,6,19,2,83,69,49,15,48,13,6,3,85,4,17,
+  19,6,49,49,52,32,50,55,49,24,48,22,6,3,85,4,8,12,15,83,116,111,99,107,104,
+  111,108,109,115,32,108,195,164,110,49,18,48,16,6,3,85,4,7,19,9,83,116,111,99,
+  107,104,111,108,109,49,26,48,24,6,3,85,4,9,12,17,86,97,108,104,97,108,108,97,
+  118,195,164,103,101,110,32,55,57,49,37,48,35,6,3,85,4,10,12,28,75,117,110,
+  103,108,105,103,97,32,84,101,107,110,105,115,107,97,32,72,195,182,103,115,
+  107,111,108,97,110,49,12,48,10,6,3,85,4,11,19,3,73,84,65,49,29,48,27,6,3,85,
+  4,3,19,20,110,115,45,118,105,112,45,48,49,46,115,121,115,46,107,116,104,46,
+  115,101,48,130,1,34,48,13,6,9,42,134,72,134,247,13,1,1,1,5,0,3,130,1,15,0,48,
+  130,1,10,2,130,1,1,0,166,33,67,34,241,62,140,127,233,46,254,30,221,209,182,
+  44,139,207,232,43,36,138,78,153,18,175,55,128,110,229,13,134,105,211,249,84,
+  204,189,189,176,231,127,10,112,242,167,58,17,70,21,17,119,47,55,218,214,62,
+  244,188,171,139,89,183,203,169,1,206,93,173,24,171,76,219,154,245,77,20,127,
+  84,182,27,105,154,254,238,143,154,60,184,174,228,77,35,69,216,92,218,90,121,
+  183,130,14,144,114,76,88,0,4,181,120,111,112,141,27,223,73,36,176,205,188,52,
+  123,252,183,182,248,77,250,252,94,175,54,87,242,136,152,225,209,86,154,217,
+  143,69,255,113,19,95,11,145,11,172,227,80,9,60,177,254,225,32,151,110,155,
+  137,159,133,104,222,68,228,173,154,118,49,154,56,109,158,143,7,252,182,231,
+  177,104,192,211,168,146,68,6,253,8,58,192,229,254,245,101,191,204,112,163,
+  241,26,168,125,161,33,154,152,45,87,35,164,150,2,100,13,50,205,241,159,60,
+  235,214,104,248,219,118,77,224,242,61,100,107,248,140,69,73,86,66,92,9,196,
+  47,74,130,49,128,235,28,12,217,40,153,3,2,3,1,0,1,163,130,1,133,48,130,1,129,
+  48,31,6,3,85,29,35,4,24,48,22,128,20,12,189,147,104,12,243,222,171,163,73,
+  107,43,55,87,71,234,144,227,185,237,48,29,6,3,85,29,14,4,22,4,20,220,21,64,
+  117,11,185,137,252,236,135,28,40,51,178,241,101,243,183,42,113,48,14,6,3,85,
+  29,15,1,1,255,4,4,3,2,5,160,48,12,6,3,85,29,19,1,1,255,4,2,48,0,48,29,6,3,85,
+  29,37,4,22,48,20,6,8,43,6,1,5,5,7,3,1,6,8,43,6,1,5,5,7,3,2,48,34,6,3,85,29,
+  32,4,27,48,25,48,13,6,11,43,6,1,4,1,178,49,1,2,2,29,48,8,6,6,103,129,12,1,2,
+  2,48,58,6,3,85,29,31,4,51,48,49,48,47,160,45,160,43,134,41,104,116,116,112,
+  58,47,47,99,114,108,46,116,99,115,46,116,101,114,101,110,97,46,111,114,103,
+  47,84,69,82,69,78,65,83,83,76,67,65,46,99,114,108,48,109,6,8,43,6,1,5,5,7,1,
+  1,4,97,48,95,48,53,6,8,43,6,1,5,5,7,48,2,134,41,104,116,116,112,58,47,47,99,
+  114,116,46,116,99,115,46,116,101,114,101,110,97,46,111,114,103,47,84,69,82,
+  69,78,65,83,83,76,67,65,46,99,114,116,48,38,6,8,43,6,1,5,5,7,48,1,134,26,104,
+  116,116,112,58,47,47,111,99,115,112,46,116,99,115,46,116,101,114,101,110,97,
+  46,111,114,103,48,51,6,3,85,29,17,4,44,48,42,130,20,110,115,45,118,105,112,
+  45,48,49,46,115,121,115,46,107,116,104,46,115,101,130,6,107,116,104,46,115,
+  101,130,10,119,119,119,46,107,116,104,46,115,101,48,13,6,9,42,134,72,134,247,
+  13,1,1,5,5,0,3,130,1,1,0,174,206,231,39,9,125,240,24,18,81,52,193,118,3,201,
+  18,26,144,85,135,110,139,142,210,95,67,250,122,79,51,63,41,43,50,30,44,70,
+  120,235,251,2,43,209,62,53,221,192,144,34,41,47,72,89,126,217,82,42,192,224,
+  222,106,105,2,3,33,48,185,246,253,59,177,29,233,76,148,74,157,192,222,255,
+  237,248,141,60,108,236,5,139,184,124,26,169,25,215,91,35,175,81,89,255,245,
+  39,52,118,93,234,59,234,68,58,80,44,32,220,72,171,97,252,59,206,151,149,243,
+  87,45,245,252,88,112,81,50,105,184,134,215,201,123,134,102,4,155,253,210,120,
+  167,145,13,198,22,106,233,62,132,31,228,131,185,115,8,157,170,100,82,36,254,
+  196,12,16,73,136,236,155,232,54,224,31,173,102,48,126,191,97,27,127,66,107,3,
+  80,209,183,134,158,80,0,43,18,94,83,98,2,213,38,229,245,199,1,187,82,69,69,
+  203,12,69,58,254,99,194,31,27,232,13,150,30,90,254,240,201,247,195,39,72,150,
+  105,241,6,104,213,53,195,138,113,36,251,107,82,29,84,121,138,41,245,160,225,
+  245,15,173>>).
+-define(C1,
+  <<48,130,4,152,48,130,3,128,160,3,2,1,2,2,16,75,200,20,3,47,7,250,106,164,240,
+  218,41,223,97,121,186,48,13,6,9,42,134,72,134,247,13,1,1,5,5,0,48,129,151,49,
+  11,48,9,6,3,85,4,6,19,2,85,83,49,11,48,9,6,3,85,4,8,19,2,85,84,49,23,48,21,6,
+  3,85,4,7,19,14,83,97,108,116,32,76,97,107,101,32,67,105,116,121,49,30,48,28,
+  6,3,85,4,10,19,21,84,104,101,32,85,83,69,82,84,82,85,83,84,32,78,101,116,119,
+  111,114,107,49,33,48,31,6,3,85,4,11,19,24,104,116,116,112,58,47,47,119,119,
+  119,46,117,115,101,114,116,114,117,115,116,46,99,111,109,49,31,48,29,6,3,85,
+  4,3,19,22,85,84,78,45,85,83,69,82,70,105,114,115,116,45,72,97,114,100,119,97,
+  114,101,48,30,23,13,48,57,48,53,49,56,48,48,48,48,48,48,90,23,13,50,48,48,53,
+  51,48,49,48,52,56,51,56,90,48,54,49,11,48,9,6,3,85,4,6,19,2,78,76,49,15,48,
+  13,6,3,85,4,10,19,6,84,69,82,69,78,65,49,22,48,20,6,3,85,4,3,19,13,84,69,82,
+  69,78,65,32,83,83,76,32,67,65,48,130,1,34,48,13,6,9,42,134,72,134,247,13,1,1,
+  1,5,0,3,130,1,15,0,48,130,1,10,2,130,1,1,0,195,227,72,196,47,92,193,203,169,
+  153,253,27,162,131,93,138,61,173,58,208,226,164,67,31,77,14,254,53,37,48,165,
+  105,27,196,232,229,193,143,84,126,225,106,162,154,92,92,222,61,252,2,206,150,
+  184,95,143,131,91,204,96,64,144,248,228,182,58,37,156,95,20,81,236,177,231,
+  175,158,80,161,49,85,199,2,189,172,82,138,127,53,142,130,250,132,173,21,254,
+  162,127,131,16,58,85,83,148,44,1,22,116,148,84,99,40,163,242,91,41,61,148,
+  136,128,32,226,20,89,33,25,180,164,152,225,96,230,242,235,162,128,131,67,224,
+  173,104,243,121,25,139,104,67,81,63,138,155,65,133,12,53,140,93,181,241,182,
+  229,167,195,131,181,107,35,111,212,165,235,80,229,148,241,74,95,238,39,75,20,
+  18,21,36,76,13,207,98,141,183,0,33,173,58,50,15,88,11,95,30,155,209,223,157,
+  142,169,25,53,80,47,65,169,173,59,198,224,69,178,83,57,127,33,191,34,26,135,
+  92,52,174,82,111,7,125,162,11,78,159,43,121,166,125,19,221,245,127,131,124,
+  47,90,93,119,120,120,145,160,20,191,125,2,3,1,0,1,163,130,1,62,48,130,1,58,
+  48,31,6,3,85,29,35,4,24,48,22,128,20,161,114,95,38,27,40,152,67,149,93,7,55,
+  213,133,150,157,75,210,195,69,48,29,6,3,85,29,14,4,22,4,20,12,189,147,104,12,
+  243,222,171,163,73,107,43,55,87,71,234,144,227,185,237,48,14,6,3,85,29,15,1,
+  1,255,4,4,3,2,1,6,48,18,6,3,85,29,19,1,1,255,4,8,48,6,1,1,255,2,1,0,48,24,6,
+  3,85,29,32,4,17,48,15,48,13,6,11,43,6,1,4,1,178,49,1,2,2,29,48,68,6,3,85,29,
+  31,4,61,48,59,48,57,160,55,160,53,134,51,104,116,116,112,58,47,47,99,114,108,
+  46,117,115,101,114,116,114,117,115,116,46,99,111,109,47,85,84,78,45,85,83,69,
+  82,70,105,114,115,116,45,72,97,114,100,119,97,114,101,46,99,114,108,48,116,6,
+  8,43,6,1,5,5,7,1,1,4,104,48,102,48,61,6,8,43,6,1,5,5,7,48,2,134,49,104,116,
+  116,112,58,47,47,99,114,116,46,117,115,101,114,116,114,117,115,116,46,99,111,
+  109,47,85,84,78,65,100,100,84,114,117,115,116,83,101,114,118,101,114,95,67,
+  65,46,99,114,116,48,37,6,8,43,6,1,5,5,7,48,1,134,25,104,116,116,112,58,47,47,
+  111,99,115,112,46,117,115,101,114,116,114,117,115,116,46,99,111,109,48,13,6,
+  9,42,134,72,134,247,13,1,1,5,5,0,3,130,1,1,0,78,35,238,72,156,246,133,139,
+  113,196,10,110,115,147,114,192,58,142,128,138,217,179,202,178,212,1,156,40,
+  207,242,92,14,33,68,147,11,182,26,33,227,152,1,148,14,103,73,129,30,190,61,
+  13,78,96,218,239,160,49,78,149,239,243,221,122,90,130,32,67,182,161,99,67,
+  179,80,105,67,98,75,86,98,176,52,138,185,19,67,89,147,236,20,121,136,243,72,
+  147,232,157,201,250,135,114,12,107,86,160,195,21,141,104,165,135,31,113,45,
+  230,90,109,60,105,113,64,4,85,220,160,67,148,32,69,56,120,215,189,138,216,57,
+  198,223,9,183,90,154,169,3,184,40,16,120,205,191,1,27,90,17,62,56,244,216,27,
+  52,121,207,51,210,1,253,172,152,205,109,71,17,144,76,187,185,91,216,112,231,
+  213,175,182,204,196,134,230,117,192,158,41,182,43,15,42,165,105,2,13,227,233,
+  162,180,93,192,243,206,44,106,133,56,118,97,198,73,130,171,81,179,130,166,
+  185,65,152,40,152,251,107,254,138,22,255,49,126,84,71,168,60,220,67,38,169,
+  155,5,183,158,192,52,67,145,48,212,50,195,17,90,225>>).