Implement cert chain validation.

NOTE: Presence of and constraints on names are not being validated.

4 files changed, 364 insertions, 2 deletions

diff --git a/src/catlfish.erl b/src/catlfish.erl
index e261824..cd871f5 100644
--- a/src/catlfish.erl
+++ b/src/catlfish.erl
@@ -3,7 +3,9 @@
 
 -module(catlfish).
 -export([add_chain/2, entries/2, entry_and_proof/2]).
+-export([known_roots/0, update_known_roots/0]).
 -include("$CTROOT/plop/include/plop.hrl").
+-include_lib("eunit/include/eunit.hrl").
 
 -define(PROTOCOL_VERSION, 0).
 
@@ -162,3 +164,107 @@ decode_tls_vector(Binary, LengthLen) ->
     <<Length:LengthLen/integer-unit:8, Rest/binary>> = Binary,
     <<ExtractedBinary:Length/binary-unit:8, Rest2/binary>> = Rest,
     {ExtractedBinary, Rest2}.
+
+-define(ROOTS_TABLE, catlfish_roots).
+
+update_known_roots() ->
+    case application:get_env(catlfish, known_roots_path) of
+        {ok, Dir} -> update_known_roots(Dir);
+        undefined -> []
+    end.
+
+update_known_roots(Directory) ->
+    known_roots(Directory, update_tab).
+
+known_roots() ->
+    case application:get_env(catlfish, known_roots_path) of
+        {ok, Dir} -> known_roots(Dir, use_cache);
+        undefined -> []
+    end.
+
+-spec known_roots(file:filename(), use_cache|update_tab) -> list().
+known_roots(Directory, CacheUsage) ->
+    case ets:info(?ROOTS_TABLE) of
+        undefined ->
+            read_pemfiles_from_dir(
+              ets:new(?ROOTS_TABLE, [set, protected, named_table]),
+              Directory);
+        _ ->
+            case CacheUsage of
+                use_cache ->
+                    ets:lookup_element(?ROOTS_TABLE, list, 2);
+                update_tab ->
+                    read_pemfiles_from_dir(?ROOTS_TABLE, Directory)
+            end
+    end.
+
+-spec read_pemfiles_from_dir(ets:tab(), file:filename()) -> list().
+read_pemfiles_from_dir(Tab, Dir) ->
+    DerList =
+        case file:list_dir(Dir) of
+            {error, enoent} ->
+                [];                             % FIXME: log enoent
+            {error, _Reason} ->
+                [];                             % FIXME: log Reason
+            {ok, Filenames} ->
+                Files = lists:filter(
+                          fun(F) ->
+                                  string:equal(".pem", filename:extension(F))
+                          end,
+                          Filenames),
+                ders_from_pemfiles(Dir, Files)
+        end,
+    true = ets:insert(Tab, {list, DerList}),
+    DerList.
+
+ders_from_pemfiles(Dir, Filenames) ->
+    L = [ders_from_pemfile(filename:join(Dir, X)) || X <- Filenames],
+    lists:flatten(L).
+
+ders_from_pemfile(Filename) ->
+    Pems = case (catch public_key:pem_decode(pems_from_file(Filename))) of
+               {'EXIT', _} -> [];
+               P -> P
+           end,
+    [der_from_pem(X) || X <- Pems].
+
+-include_lib("public_key/include/public_key.hrl").
+der_from_pem(Pem) ->
+    case Pem of
+        {_Type, Der, not_encrypted} ->
+            case (catch public_key:pkix_decode_cert(Der, otp)) of
+                {'EXIT', _} ->
+                    [];
+                #'OTPCertificate'{} ->
+                    Der;
+                _Unknown ->
+                    []
+            end;
+        _ -> []
+    end.
+
+pems_from_file(Filename) ->
+    {ok, Pems} = file:read_file(Filename),
+    Pems.
+
+%%%%%%%%%%%%%%%%%%%%
+%% Testing internal functions.
+-define(PEMFILES_DIR_OK, "../test/testdata/known-roots").
+-define(PEMFILES_DIR_NONEXISTENT, "../test/testdata/nonexistent-dir").
+
+read_pemfiles_test_() ->
+    {setup,
+     fun() -> {known_roots(?PEMFILES_DIR_OK, use_cache),
+               known_roots(?PEMFILES_DIR_OK, use_cache)}
+     end,
+     fun(_) -> ets:delete(?ROOTS_TABLE) end,
+     fun({L, LCached}) ->
+             [?_assertMatch(7, length(L)),
+              ?_assertEqual(L, LCached)]
+     end}.
+
+read_pemfiles_fail_test_() ->
+    {setup,
+     fun() -> known_roots(?PEMFILES_DIR_NONEXISTENT, use_cache) end,
+     fun(_) -> ets:delete(?ROOTS_TABLE) end,
+     fun(Empty) -> [?_assertMatch([], Empty)] end}.
diff --git a/src/v1.erl b/src/v1.erl
index ba5c456..46b5235 100644
--- a/src/v1.erl
+++ b/src/v1.erl
@@ -22,7 +22,13 @@
                         html("add-chain: invalid base64-encoded chain: ",
                              [ChainBase64]);
                     [LeafCert | CertChain] ->
-                        catlfish:add_chain(LeafCert, CertChain);
+                        Roots = catlfish:known_roots(),
+                        case x509:normalise_chain(Roots, [LeafCert|CertChain]) of
+                            {ok, [Leaf | Chain]} ->
+                                catlfish:add_chain(Leaf, Chain);
+                            {Err, Msg} ->
+                                html("add-chain: ", [Msg, Err])
+                        end;
                     Invalid ->
                         html("add-chain: chain is not a list: ", [Invalid])
                 end;
@@ -125,7 +131,9 @@
     deliver(SessionID, R).
 
 'get-roots'(SessionID, _Env, _Input) ->
-    R = [{certificates, []}],                   % NIY.
+    R = [{certificates,
+          [base64:encode(Der) ||
+              Der <- catlfish:update_known_roots()]}],
     deliver(SessionID, binary_to_list(jiffy:encode({R}))).
 
 %% Private functions.
diff --git a/src/x509.erl b/src/x509.erl
new file mode 100644
index 0000000..aef9ae7
--- /dev/null
+++ b/src/x509.erl
@@ -0,0 +1,137 @@
+%%% 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 der_encoded() :: public_key:der_encoded().
+-type reason() :: {chain_too_long | root_unknown | chain_broken}.
+
+-define(MAX_CHAIN_LENGTH, 10).
+
+-spec normalise_chain([der_encoded()], [der_encoded()]) -> [der_encoded()].
+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([der_encoded()], [der_encoded()], 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(der_encoded(), [der_encoded()]) -> 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(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
+
+%%%%%%%%%%%%%%%%%%%%
+%% 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))
+    ].
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,
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