Certificate revocation and the performance of OCSP

Certificate revocation is a critical aspect of maintaining the security of the third-party Certificate Authority (CA) infrastructure which underpins secure communication on the internet using SSL/TLS. A certificate may be worth revoking when it has had its private key compromised, the owner of the certificate no longer controls the domain for which it was issued, or the certificate was mistakenly signed. Without the ability to revoke certificates, a CA has no direct means of marking a certificate as untrusted before the expiry of the certificate, which could be several years away. In particularly urgent cases a browser vendor may have the ability to block certain individual certificates, trusted roots, or intermediate certificates, but this is rarely performed and is not suitable for lower-risk issues where revocation is necessary but not urgent.

There are two main technologies for browsers to check the revocation status of a particular certificate: using the Online Certificate Status Protocol (OCSP) or looking up the certificate in a Certificate Revocation List (CRL). OCSP provides real-time revocation information about an individual certificate from an issuing CA, unlike CRLs which provide a list of revoked certificates and may be received by clients less frequently.

The graph below shows a comparison of the time taken for the TLS handshake, both with and without OCSP checking enabled. The data was collected using packet traces taken while using Firefox 20 on Linux from an IP address in the UK. Measurements were taken three times (each time with a fresh cache) after discarding an initial request.

The relationship between whether OCSP checking is enabled and the time taken to complete the TLS handshake is not straightforward. In order for the browser to display the "green bar" to distinguish an Extended Validation (EV) certificate, OCSP requests must be made for every certificate in the chain whereas in many browsers, if an OCSP request is made at all, intermediate certificates are not checked. The increased time taken for the TLS handshake when using an EV certificate can be attributed to Firefox's sequential OCSP checking behaviour. However, where an OCSP check can be performed within the round-trip time to the server — for example, if the OCSP responder is served via a content delivery network or CDN — the check does not dramatically affect the time taken for the TLS handshake. When both the web server and the OCSP responder are topologically close to the client, as is the case with www.globalsign.com, the short round-trip time to the server isn't sufficient to mask the the time taken to receive OCSP responses for both the web site's certificate and the intermediate certificate presented. The slight difference between Paypal and GlobalSign's performance can at least partially be attributed to the additional OCSP request made for GlobalSign: GlobalSign's certificate chain requires three OCSP requests whereas Paypal's requires just two.

Reliability of RapidSSL's OCSP responder — December 2012

Netcraft has extracted around 40 OCSP responder URLs from certificates seen in the Netcraft SSL server survey, and has been monitoring them since late November 2012. The performance and reliability of the services varies significantly: Symantec's VeriSign OCSP responder has had consistently solid reliability, only a handful of connections failed over a 4 month period; whereas, in the same period more than 6% of requests to one of StartCom's responders failed. The reliability and performance of StartCom's OCSP responders have improved significantly since the end of February 2013 when it switched to using Akamai. Geotrust, another Symantec brand, did not have as strong a performance as either Thawte or VeriSign — all three of GeoTrust’s OCSP servers were down for between 48 and 104 minutes in a single event. Performance and reliability is measured from 11 points spread around Europe and North America: outages require at least one failed response from all measurement nodes within the 15-minute measurement interval.

Shift in reliability and performance for StartCom — late February 2013

For those browsers performing a synchronous OCSP request during the TLS handshake, the performance of the OCSP responder is often crucial. Any delay in responding to the request may noticeably slow down the handshake. For example, comparing GlobalSign's CloudFlare-accelerated OCSP responder with Entrust's, you find that GlobalSign's responder is significantly faster than Entrust's which uses Akamai's CDN. However, despite GlobalSign's performance advantage, its reliability has been affected by a number of CloudFlare outages — since Netcraft began monitoring OCSP, GlobalSign's responders have had at least 45 minutes of downtime whereas Entrust has had none.

GlobalSign (blue) and Entrust (green) OCSP responder performance.

OCSP responses can be stapled to a response from a web server when negotiating the TLS handshake to avoid the need for the browser to make a secondary request to a third party server. CloudFlare has claimed that enabling OCSP stapling has led to a 30% speed improvement for HTTPS sites. OCSP stapling support is present in newer versions of nginx — an increasingly popular open source web server — as a result of a development project sponsored by GlobalSign, DigiCert, and Comodo. OCSP stapling is not supported in the most popular version of Apache, 2.2.x, nor is it supported in current versions of Firefox (although support is in the pipeline), so it must remain only part of the solution for the foreseeable future. Frustrated by some of the limitations of OCSP, some CAs have lent support to a proposed an alternative revocation method using short lived certificates.

Browser support for the both OCSP and CRLs is mixed: currently, Firefox does not automatically download the CRLs from trusted CAs, so Firefox users must rely on OCSP alone; Google uses a proprietary mechanism to distribute CRLs to users of Google Chrome which aggregates per-CA CRLs into a single update which is distributed using its automatic update channel. Many browsers default to a "soft-fail" approach, leaving users vulnerable to eavesdroppers able to block or tamper with OCSP traffic. For as long as the CAs running OCSP responders do not have a strong record for both the performance and the reliability of their OCSP responders, browsers will find it difficult to justify switching to synchronous "hard-fail" behaviour.

Updated 18/04/2013

Angry Birds impersonated to distribute malware

As part of Netcraft's ongoing work in providing anti-fraud and anti-phishing services, we have recently discovered a significant number of Russian language attacks targeting users of popular pieces of software, including well known brands such as Angry Birds. This type of attack can be particularly successful as it exploits a user's trust in a brand. Malicious downloads for Android phones are becoming an increasingly common attack vector.

Angry Birds is a video game franchise created by Rovio Entertainment. The franchise gained popularity on Apple's iOS platform, and has since become available on all popular mobile and desktop operating systems. With over 1 billion downloads, and over 250 million active users, the franchise has become iconic in the marketplace — the original game and its variants are frequently seen in top ten app lists, so is continually attracting new users.

Angry Birds is impersonated to push malware.

Distributing malware purporting to be genuine software isn't a new tactic — Angry Birds has been a victim of this before. In this case smartphone users were hit by premium rate phone scams.

However, lately we have seen an increase in attackers taking additional measures to prevent their sites being found and taken down by the anti-phishing community. Restricting access to a site by country is one tactic that is becoming increasingly common. This is usually achieved via IP filtering; however Netcraft has seen attacks restricting access based on Accept-Language and User-Agent headers — one particular type of attack purported to provide a browser update, varying the brand impersonated depending on the User-Agent submitted.

Many of the attacks Netcraft has observed have been primarily composed of Russian language content, and restricted to IP addresses located in Russian-speaking countries. On another site impersonating Angry Birds, we found that when accessed from a proxy based in Russia, malware was distributed; however when attempting to download the content through a different proxy (located in Australia in the below example) we were redirected to Google.

IP filtering, amongst other measures taken by fraudsters, makes identifying and classifying phishing sites more difficult both for anti-phishing vendors and for hosting companies responding to abuse notifications.

You can protect yourself against phishing sites by installing Netcraft's Anti-Phishing Extension and help protect the internet community by reporting potential phishing sites to Netcraft by email to scam@netcraft.com or at http://toolbar.netcraft.com/report_url. Netcraft can also help protect both brand owners and hosting companies.

Mt.Gox “victim of own success” as Bitcoins fall in value

After days of intense growth, Bitcoins peaked at an unprecedented value of $266 last night, shortly before a crash which saw some investors selling them for as little as $105.

Value of 1 Bitcoin (BTC) in USD, midday 10 April - midday 11 April 2013 BST. [Source: Mt.Gox]

The Bitcoin market showed signs of recovery the following morning, but started falling again during an outage at Mt.Gox, which handles the majority of all Bitcoin trade.

Mt.Gox announced on Facebook that last night's crash was not caused by a DDoS (distributed denial of service) attack, but rather as a result of increased trade and new users signing up. The increased trade caused the Mt.Gox trading system to lag, which caused panic amongst some investors who started "cashing out" their Bitcoins, further exacerbating the situation until the trade engine froze.

Mt.Gox also revealed that the number of trades had tripled in a 24 hour period, and the number of new accounts jumped from 60,000 in March to 75,000 in just the first few days of April. Around 20,000 accounts are now being created each day, which is not surprising, given the potential investment value that has become widely evident over the past few weeks.

One investor was fortunate enough to have sold nearly 70,000 Bitcoins ahead of the crash. These would have been worth more than $18 million if sold at the very peak of the market, which demonstrates just how remarkable the growth has been — less than 3 years ago, 10,000 Bitcoins were used to buy $25's worth of pizza.

Mt.Gox went down for a short period late this morning (Thursday) while it performed some system maintenance and added several new servers to its system; however, as soon as this maintenance was completed, Mt.Gox was subjected to another DDoS attack.

mtgox.com is hosted by Prolexic, a company specialising in DDoS protection and mitigation, whilst the read-only APIs on data.mtgox.com are served via CloudFlare's content delivery network.

Dynamically updating performance graphs of the most popular Bitcoin trading sites are available here.

Fake Mulberry stores promoted by hacked sites and black hat SEO

Mulberry — well known for its luxury fashion accessories — is currently being impersonated by fake online stores which have successfully promoted themselves to the first page of search engine results by planting malign JavaScript on hacked websites.

The hacked sites display various descriptions of Mulberry products, and also include hyperlinks to the fake Mulberry sites. Both help to make the fake sites seem more relevant to search engines; indeed, the fake stores can even be reached from the first page of organic Google search results for the search term "Mulberry".

The injected scripts are sourced from an external site hosted in China, but which uses the .la country code top-level domain. This ccTLD belongs to the Lao People's Democratic Republic, but is actively marketed as a top-level domain for the US city of Los Angeles. Although the fake store associated with the above screenshot uses a UK ccTLD, it is actually hosted by root S.A. in Luxembourg, and shares the same netblock as kim.com and several bittorrent sites, including a mirror of The Pirate Bay, allowing the site to be accessed from countries where ISPs were ordered to implement blocks against the original Pirate Bay site.

Such underhanded methods of search engine optimisation (SEO) are not unusual, and can potentially outperform traditional spam-based marketing. For instance, there is likely to be a much larger conversion rate among customers who are actively searching for a specific product than there would be among recipients of spam, many of whom would have no intention of buying anything, and – thanks to spam filters – may not even receive the spam in the first place. With such low returns on spam-based marketing, a huge number of emails would need to be sent in order to achieve a worthwhile return, which would only serve to draw more – possibly unwanted – attention to a fake site.

Some of the hacked sites which appear on the first page of a Google search for "Mulberry" lend further credibility to the scam, making it appear as though the products for sale have received thousands of reviews and near-perfect ratings. However, clicking on these links causes the user to be redirected to one of the fake stores, such as http://www.mulberryeshop.co.uk.

Even if you arrive at a website via a trusted search engine, Netcraft's site reports can help you make informed decisions about whether that site itself should be trusted. For example, Netcraft's site report awards a Risk Rating of 9/10 to www.mulberryeshop.co.uk, whereas the legitimate site, www.mulberry.com, has a rating of 0/10. Such ratings are conveniently accessible to users of the Netcraft browser extension, which is available for Firefox and Chrome.

Other obvious clues to look out for are the lack of an encrypted HTTPS connection when logging in to the site, and the WHOIS record for the domain reveals that "the registrant is a non-trading individual who has opted to have their address omitted from the WHOIS service."

A fake Mulberry online store, hosted in Luxembourg

Brand owners can also take the initiative to protect both themselves and their customers. The fake store shown above was detected last month by Netcraft's phishing, identity theft and fraud detection service, demonstrating how brand owners can receive early warnings of such attacks.

Mulberry's extraordinary success over the past five years (LON:MUL) has made it an attractive brand to target, even though its shares dropped by 16% last month. This drop followed a profit warning, which revealed weaker than anticipated trading post-Christmas. It is plausible that a multitude of fake stores, with good search engine rankings, could have contributed towards this reduction in revenue.

Bitcoin success attracts hacking, phishing, and fraud

Bitcoin, a distributed digital currency that cryptographically verifies transactions, has recently seen a large increase in usage — the total amount of Bitcoins in circulation is now well over $1B US Dollars and each Bitcoin is today worth more than $100. By way of comparison, Gibraltar — a British Overseas Territory and a conventional tax haven — had an economy worth an estimated $1.275B in 2008.

Speculators, investors, and criminals alike have been drawn to the alternative currency in the hopes of exploiting its anonymity, its almost exponential rising exchange rate against conventional currencies, and its dominant position amongst non-governmental currencies. Its attraction to criminals is diverse: it has become the de facto equivalent of cash facilitating anonymous purchases of illegal goods, and the dramatic increase in the value of each Bitcoin has meant that Bitcoin wallets have become increasingly attractive targets for would-be phishers.

Mt. Gox Phishing Site

A recent phishing attack against the leading Bitcoin Exchange, Mt. Gox

Bitcoin users are no strangers to being targeted by criminals: last month, attackers were able to steal $12,000 worth of Bitcoins from Bitinstant, a Bitcoin transaction services company, by obtaining the credentials for a brokerage account after socially engineering access to their emails. Malware writers have also targeted Bitcoins: Infostealer.Coinbit is a Trojan horse that tries to steal Bitcoin wallets. Criminals have also been using networks of infected computers to mine Bitcoins for themselves.

Bitcoin exchanges, organisations converting between Bitcoins and conventional currencies, are an obvious target for fraudsters. Last Thursday Mt. Gox (the leading Bitcoin exchange) faced a “stronger than average” DDoS attack. In September 2012 Bitfloor (another Bitcoin exchange) suspended operations after the theft of ~24,000 BTC (worth $250,000 at the time), and the Bitcoin exchange, Bitcoinica, went out of business after also suffering from large thefts.

Despite the apparent risk of operating in this business, some organisations are promoting a laissez-faire attitude to security to the Bitcoin community: BitPay recommends that merchants "[..] can eliminate the need for PCI Compliance and expensive security measures" by replacing credit card transactions with Bitcoin-based solutions.

Netcraft can provide Phishing Site Takedown and Countermeasures services, PCI Approved Vulnerability Scanning and Penetration Testing to Bitcoin exchanges, merchants, and e-commerce sites. For more information, please contact sales@netcraft.com. Internet users can be protected against phishing sites, Bitcoin-related or otherwise, by Netcraft's Anti-Phishing Extension. Help protect the internet community by reporting potential phishing sites to Netcraft by email to scam@netcraft.com or at http://toolbar.netcraft.com/report_url.

April 2013 Web Server Survey

In the April 2013 survey we received responses from 649,072,682 sites, 17.6M more than last month.

This month, market leader Apache lost 9.9M sites, or 3 percentage points of market share. A major contributor to this loss was the movement of a large affiliate referral network consisting of around 8M sites now being served by nginx. Apache is now used by just over 51% of websites, which is still substantially more than its closest competitor Microsoft IIS. IIS gained 1.95 percentage points of market share this month (an increase of 15.8M hostnames) bringing its market share to almost 20%. Meanwhile, nginx saw an overall growth of 10.6M sites this month, with the largest nginx hosting company, Hetzner Online AG, contributing an additional 1.6M sites.

In terms of active sites the survey was less volatile. Apache still experienced an overall loss, however much smaller at just 288k active sites. The biggest increase came from nginx, and was unrelated to their large hostname gain described earlier, with Peer1 Networks gaining 1.5M nginx active sites.

North Korea's drew the world's attention to its web presence by accusing the United States and its allies of "intensive and persistent virus attacks" on servers operated by the North Korean regime. The Korean Central News Agency's press release goes on to assert that:

"It is nobody's secret that the U.S. and south Korean puppet regime are massively bolstering up cyber forces in a bid to intensify the subversive activities and sabotages against the DPRK [Democratic People's Republic of Korea]."

There is only a very small number of North Korean sites accessible from outside of the country; however, these sites do make use of several modern and popular web technologies from around the globe. The Rodong Sinmun newspaper's site uses PHP and CentOS 5, and hosts an HTTPS service with an expired self-signed certificate. More controversially, The Korean Central News Agency's official website uses Java, Flash and jQuery and is hosted using Apache 2.2.3 on a server running Red Hat Enterprise Linux 5, a commercial Linux distribution which is owned, distributed and supported by American multinational Red Hat, Inc. Red Hat Enterprise Linux is subject to U.S. export controls, which specifically prohibit its use in North Korea. As a result, this installation is likely unlicensed and so may not receive security updates.

Meanwhile in South Korea, the Government of Korea, an SSL certificate authority (CA) trusted by Microsoft has revoked the last of more than 100 unusual SSL certificates each of which could have allowed its owner to act as a trusted CA. With the ability conferred by the cA bit being set in the Basic Constraints extension, a forged certificate signed using the mis-issued certificate could be trusted for any site by users of some SSL implementations. Any such certificate could be used to perform man-in-the-middle attacks on users of third-party websites in order to view the contents of any intercepted encrypted traffic. There is an additional property which is usually required for a certificate to be considered a valid intermediate — ‘Certificate Signing’ should be set as a permissible Key Usage — but some implementations may ignore this extra requirement. None of the Korean certificates found had the necessary flags set in this additional extension, so most implementations would not trust such forged certificates.

The certificates found appear to have been issued to South Korean academic institutions without the intention of them being able to sign additional certificates. These certificates have been in the Netcraft SSL Server Survey for some time but no longer pose a risk: all of the certificates concerned have either been revoked or have expired. The most recent revocation was on January 31st 2013 for a certificate issued in late 2011, showing it was at risk of misuse for more than a year.

DeveloperMarch 2013PercentApril 2013PercentChange
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