Refuse to accept certificate chains containing any RSA public key smaller

net/base/x509_certificate.cc

Index: net/base/x509_certificate.cc
===================================================================
--- net/base/x509_certificate.cc	(revision 114272)
+++ net/base/x509_certificate.cc	(working copy)
@@ -224,6 +224,16 @@
 }
 #endif
 
+bool IsWeakKey(X509Certificate::PublicKeyType type, size_t size_bits) {
+  switch (type) {
+    case X509Certificate::kPublicKeyTypeRSA:
+    case X509Certificate::kPublicKeyTypeDSA:
+      return size_bits < 1024;
+    default:
+      return false;

[wtc, 2011/12/14 00:18:03]

Nit: I think it's important to document here or before this
function that this function may return false negatives.

+   }

[Ryan Sleevi, 2011/12/13 23:54:16]

nit: whitespace

+}
+
 }  // namespace
 
 bool X509Certificate::LessThan::operator()(X509Certificate* lhs,
@@ -597,6 +607,31 @@
     rv = MapCertStatusToNetError(verify_result->cert_status);
   }
 
+  // Check for weak keys in the entire verified chain.
+  size_t size_bits = 0;
+  PublicKeyType type = kPublicKeyTypeUnknown;
+  bool weak_key = false;
+
+  GetPublicKeyInfo(verify_result->verified_cert->os_cert_handle(), &size_bits,
+                   &type);
+  if (IsWeakKey(type, size_bits)) {
+    weak_key = true;
+  } else {
+    const OSCertHandles& intermediates =
+        verify_result->verified_cert->GetIntermediateCertificates();
+    for (OSCertHandles::const_iterator i = intermediates.begin();
+         i != intermediates.end(); ++i) {
+      GetPublicKeyInfo(*i, &size_bits, &type);
+      if (IsWeakKey(type, size_bits))
+        weak_key = true;
+    }
+  }
+
+  if (weak_key) {
+    verify_result->cert_status |= CERT_STATUS_WEAK_KEY;
+    return MapCertStatusToNetError(verify_result->cert_status);

[wtc, 2011/12/14 00:18:03]

IMPORTANT: this needs the same kind of care that rsleevi used
in his treat-MD5-signature-as error CL, that we should not
overwrite a more serious error in 'rv'.

I believe the IsPublicKeyBlacklisted code above also needs
to do this.

You can do this in a separate CL since we're still very
early in the M18 development cycle.

+  }
+
   return rv;
 }