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 110129)
+++ net/base/x509_certificate.cc	(working copy)
@@ -590,6 +590,30 @@
 
   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 (type == kPublicKeyTypeRSA && size_bits < 1024)
+    weak_key = true;

[wtc, 2011/11/17 02:52:18]

It seems that a IsWeakPublicKey/ContainsWeakPublicKey function
may be more appropriate than the GetPublicKeyInfo function.
Also, it may be a good idea to create a method for the code
on lines 593-610.

Please define a constant for 1024.  Your CL's commit message
says "less than 1023 bits".  Should we use 1023 instead?

+
+  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 (type == kPublicKeyTypeRSA && size_bits < 1024)
+      weak_key = true;
+  }
+
+  if (weak_key) {
+    verify_result->cert_status |= CERT_STATUS_WEAK_KEY;
+    return MapCertStatusToNetError(verify_result->cert_status);
+  }
+
   // 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)) {