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 114041)
+++ net/base/x509_certificate.cc	(working copy)
@@ -224,6 +224,12 @@
 }
 #endif
 
+bool IsWeakKey(X509Certificate::PublicKeyType type, size_t size_bits) {
+  return size_bits < 1024 &&
+         (type == X509Certificate::kPublicKeyTypeRSA ||
+          type == X509Certificate::kPublicKeyTypeDSA);

[wtc, 2011/12/13 21:56:18]

To allow easy future expansion, please implement this function
with a switch statement:

  switch (type) {
    case X509Certificate::kPublicKeyTypeRSA:
    case X509Certificate::kPublicKeyTypeDSA:
      return size_bits < 1024;
    default:
      // False negative.
      return false;
  }
}

+}
+
 }  // namespace
 
 bool X509Certificate::LessThan::operator()(X509Certificate* lhs,
@@ -590,6 +596,31 @@
 
   int rv = VerifyInternal(hostname, flags, crl_set, verify_result);
 
+  // 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, 2011/12/13 21:56:18]

IMPORTANT: I think we should fall through to check for blacklisted
public keys, which are a more serious violation.

Alternatively, we should check for blacklisted public keys
first.

+  }
+
   // This check is done after VerifyInternal so that VerifyInternal can fill in
   // the list of public key hashes.
   if (IsPublicKeyBlacklisted(verify_result->public_key_hashes)) {