Monthly Archives: December 2012

SSL 3.0 Usage in the Wild

Recently I had an opportunity to look at some logs that showed the cipher suites and protocol versions being negotiated for a large cross-section of websites.

I have always wanted to look at data like this and as such have instrumented my own sites to look at it but let’s face it some uber geek blog or security product company website just isn’t going to have representative traffic for the internet at large.

One of the easiest and most useful things to gleam from this data is that the impact of disabling SSL 3.0 is actually quite small.

So of the sampling 2.48% of all SSL/TLS sessions were done with SSL 3.0, if we look at (and believe) the User Agents that negotiated these sessions we see 74.98% of these were Windows clients, the next biggest chunk was Gecko at 16.39%.

Browser %
Internet Explorer














Of these Windows clients 45.45% of them were Windows 2000 or XP but only 6.67% of them were running versions of Internet Explorer that did not support TLS 1.0; this basically boils down the the IE versions before version 7 as this was the first to enable TLS by default. So why did we see the remaining 68.31% of the 2.48% negotiating SSL when they support TLS?

There are a few possible explanations:

  1. Some TLS implementations will fall back to SSL in the event of a failure, one common example of a failure would be an intermittent TCP connection problem. Basically if this is the case the client had a problem reaching the server and thought it might be related to TLS and so it tried again. In this case its likely that if it had tried with TLS it probably would have succeeded also.  It also seems that its likley in this case the user did not get a working experience — the assumption here is that the TCP problems they are experiencing were not a one time thing.
  2. Some old TLS implementations had problems with TLS extensions as such some TLS implementations added logic to fall back to SSL when they encountered a this extension intolerance, again falling back to TLS (without extensions) would have likely also worked.
  3. Some enterprises may have used group policy to disable the use of TLS due to the TLS extension intolerance problems (see #2).
  4. Some clients are lying; they may be crawlers, bots and other such automated agents looking to profile these websites.

So what can we do with this data?

Well for one we can understand what interoperability implications we may encounter by disabling SSL 3.0 on our servers – on the surface the answer is up to 2.48% of clients will not be able to get to our servers.

The real answer is that it’s likely that figure is much smaller, probably half that if not even less than.

OK, so we understand the interoperability impact but why should I care? Well there are a few reasons:

  1. NIST 140-2 compliance requires disabling SSL 3 ciphers and by disabling SSL 3 you do just that.
  2. The browsers that only support this decade old protocol are nearly as old and a have a litany of issues of their own.
  3. TLS has a number of security, performance and deploy-ability enhancing  features such such as stronger cipher suites, Session Tickets and SNI that you will benefit from.

Another thing you should ask yourself is did you design your site for these old browsers? If not by leaving SSL 3 enabled you really are not getting much if any benefit since those users who require it would likely not be able to use your site effectively anyways.

When we consider this data I believe the natural conclusion is that disabling SSL 3.0 it is the right thing to do.


Understanding Windows Automatic Root Update

Windows has a feature called Automatic Root Update, when CryptoAPI does a chain build, exhausts the locally installed root certificates it downloads (if it has not already done so) a list of certificates it should trust.

This list contains attributes about those certificates (hashes of their subject name and keys, what Microsoft believes it should be trusted for, etc.).

If it finds the certificate it needs in that list it downloads it and installs it.

So how does this technically work?

There is a pre-configured location where Windows looks for this Certificate Trust List (CTL), it is

NOTE: Technically they do use different language codes in the URLs based on the client local but to the best of my knowledge they all map to the same files today.

This list is downloaded and de-compressed; you can do the same thing on Windows (with curl) like this:

mkdir authroot

cd authroot


expand .\authroot.stl

You can open authroot.stl with explorer and look at some of its contents but for the purpose of our exercise that won’t be necessary.

This file is a signed PKCS #7 file, Windows expects this to be signed with key material they own (and protect dearly).

It contains a Microsoft specific ContentInfo structure for CTLs and a few special attributes. WinCrypt.h has the OIDs for these special attributes defined in it but for brevity sake here are the ones you will need for this file: OID_CTL OID_ROOT_LIST_SIGNER OID_CERT_PROP_ID_METAEKUS CERT_FRIENDLY_NAME_PROP_ID OID_CERT_KEY_IDENTIFIER_PROP_ID OID_CERT_SUBJECT_NAME_MD5_HASH_PROP_ID CERT_ROOT_PROGRAM_CERT_POLICIES_PROP_ID OID_CERT_PROP_ID_PREFIX_98 OID_CERT_PROP_ID_PREFIX_105 szOID_ENROLL_CERTTYPE_EXTENSION szOID_CERTSRV_CA_VERSION OID_ROOT_PROGRAM_FLAGS_BITSTRING

Copy this list of OIDs and constants into a file called authroot.oids and put it where we extracted the STL file.

We can now use the following OpenSSL command to inspect the contents in more detail:

openssl asn1parse -oid authrootstl.oids -in authroot.stl -inform DER

There is lots of stuff in here, but for this exercise we will just download the certificates referenced in this list.

To do that we need to understand which of the attributes are used to construct the URL we will use to download the actual certificate.

This list values we want are just after the OID_ROOT_LIST_SIGNER, the first one being “CDD4EEAE6000AC7F40C3802C171E30148030C072”, its entry will look like this:


  128:d=8  hl=2 l=  20 prim:         OCTET STRING      [HEX DUMP]:CDD4EEAE6000AC7F40C3802C171E30148030C072

  150:d=8  hl=3 l= 246 cons:         SET

  153:d=9  hl=2 l=  30 cons:          SEQUENCE

  155:d=10 hl=2 l=  10 prim:           OBJECT            :OID_CERT_PROP_ID_PREFIX_105

  167:d=10 hl=2 l=  16 cons:           SET

  169:d=11 hl=2 l=  14 prim:            OCTET STRING      [HEX DUMP]:300C060A2B0601040182373C0302

  185:d=9  hl=2 l=  32 cons:          SEQUENCE

  187:d=10 hl=2 l=  10 prim:           OBJECT            :OID_CERT_SUBJECT_NAME_MD5_HASH_PROP_ID

  199:d=10 hl=2 l=  18 cons:           SET

  201:d=11 hl=2 l=  16 prim:            OCTET STRING      [HEX DUMP]:F0C402F0404EA9ADBF25A03DDF2CA6FA

  219:d=9  hl=2 l=  36 cons:          SEQUENCE

  221:d=10 hl=2 l=  10 prim:           OBJECT            :OID_CERT_KEY_IDENTIFIER_PROP_ID

  233:d=10 hl=2 l=  22 cons:           SET

  235:d=11 hl=2 l=  20 prim:            OCTET STRING      [HEX DUMP]:0EAC826040562797E52513FC2AE10A539559E4A4

  257:d=9  hl=2 l=  48 cons:          SEQUENCE

  259:d=10 hl=2 l=  10 prim:           OBJECT            :OID_CERT_PROP_ID_PREFIX_98

  271:d=10 hl=2 l=  34 cons:           SET

  273:d=11 hl=2 l=  32 prim:            OCTET STRING      [HEX DUMP]:885DE64C340E3EA70658F01E1145F957FCDA27AABEEA1AB9FAA9FDB0102D4077

  307:d=9  hl=2 l=  90 cons:          SEQUENCE

  309:d=10 hl=2 l=  10 prim:           OBJECT            :CERT_FRIENDLY_NAME_PROP_ID

  321:d=10 hl=2 l=  76 cons:           SET

  323:d=11 hl=2 l=  74 prim:            OCTET STRING      [HEX DUMP]:4D006900630072006F0073006F0066007400200052006F006F007400200043006500720074006900660069006300610074006500200041007500740068006F0072006900740079000000

We can download this certificate with the following command:

curl> CDD4EEAE6000AC7F40C3802C171E30148030C072.crt

If we look at the contents of the certificate we can see this is the 4096 bit “Microsoft Root Certificate Authority”.

The next in the list is 245C97DF7514E7CF2DF8BE72AE957B9E04741E85, and then the next is 18F7C1FCC3090203FD5BAA2F861A754976C8DD25 and so forth.

We could go through and parse the ASN.1 to get these values, iterate on them and download them all if we wanted. Of course if we wanted to get all of the root certificates we might as well just download the most recent root update here:

It contains the same information just in a self-contained format (this is whats used by down-level clients that do not have Automatic Root Update).

Anyhow hopefully this will be useful for someone,