From f98f39ea2e9ae9d701f79de1b45e21fa0e5fd995 Mon Sep 17 00:00:00 2001
From: Linus Nordberg <linus@nordberg.se>
Date: Fri, 20 Mar 2015 16:54:30 +0100
Subject: WIP, actually working too

---
 src/x509.erl | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/src/x509.erl b/src/x509.erl
index d088624..5abd853 100644
--- a/src/x509.erl
+++ b/src/x509.erl
@@ -296,22 +296,29 @@ set_issuer_and_authkeyid(TBSCert,
 -spec is_precert_signer(#'Certificate'{}) -> boolean().
 is_precert_signer(#'Certificate'{tbsCertificate = TBSCert}) ->
     Extensions = pubkey_cert:extensions_list(TBSCert#'TBSCertificate'.extensions),
+    %% NOTE: It's OK to look at only the first extension found since
+    %% "A certificate MUST NOT include more than one instance of a
+    %% particular extension." --RFC5280 Sect 4.2
     case pubkey_cert:select_extension(?'id-ce-extKeyUsage', Extensions) of
-        #'Extension'{extnValue = [_|?CA_POISON_OID]} ->
-            case pubkey_cert:select_extension(?'id-ce-basicConstraints',
-                                              Extensions) of
-                #'Extension'{critical = true,
-                             extnValue = #'BasicConstraints'{cA = true}} ->
-                    lager:debug("found precert signer", []),
-                    true;
-                E ->
-                    lager:debug("found poisonous ca oid but cA != true: ~p",
-                                [E]),
-                    false
+        #'Extension'{extnValue = Val} ->
+            case 'OTP-PUB-KEY':decode('ExtKeyUsageSyntax', Val) of
+                %% NOTE: We require that the poisoned OID is the
+                %% _only_ extkeyusage present. RFC6962 Sect 3.1 is not
+                %% really clear.
+                {ok, [?CA_POISON_OID]} -> is_ca(TBSCert);
+                _ -> false
             end;
-        E ->
-            lager:debug("didn't find poisonous ca oid, only ~p", [E]),
-            false
+        _ -> false
+    end.
+
+is_ca(#'TBSCertificate'{extensions = Extensions}) ->
+    case pubkey_cert:select_extension(?'id-ce-basicConstraints', Extensions) of
+        #'Extension'{critical = true, extnValue = Val} ->
+            case 'OTP-PUB-KEY':decode('BasicConstraints', Val) of
+                {ok, {'BasicConstraints', true, _}} -> true;
+                _ -> false
+            end;
+        _ -> false
     end.
 
 -spec remove_poison_ext(#'Certificate'{}) -> #'TBSCertificate'{}.
-- 
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