U.S. military cyber security fails to make the grade

The United States Department of Defense is still issuing SHA-1 signed certificates for use by military agencies, despite this practice being banned by NIST for security reasons nearly two years ago. These certificates are used to protect sensitive communication across the public internet, keeping the transmitted information secret from eavesdroppers and impersonators. The security level provided by these DoD certificates is now below the standard Google considers acceptable for consumer use on the web.

The Missile Defense Agency, the eventual successor to the "Star Wars" programme, uses one of these SHA-1 certificates on a Juniper Networks remote access device. The SHA-1 certificate was issued by the Department of Defense in February 2015, long after NIST declared this practice to be unacceptable.

The Missile Defense Agency operates a remote access service which uses a SHA-1 signed certificate, making it vulnerable to impersonation and man-in-the-middle attacks.

The Missile Defense Agency operates a remote access service which uses a SHA-1 signed certificate issued earlier this year. This makes the site vulnerable to impersonation and man-in-the-middle attacks that would facilitate unauthorised access to data.

The National Institute of Standards & Technology (NIST) is charged with "developing standards and guidelines, including minimum requirements, for providing adequate information security for all agency operations and assets", though its requirements "shall not apply to national security systems". Whilst these Department of Defense systems may or may not be considered national security systems, it is difficult to see why they would be subject to requirements any less stringent than those recommended by NIST.

The SHA-1 algorithm was first published in 1995 and is no longer considered secure. NIST's decision to disallow SHA-1 signature generation after 2013 was originally due to concerns surrounding the cryptographic strength of the algorithm. Back then, it was thought quite likely that future advancements in computing technology and the discovery of new attacks would allow attackers to find SHA-1 hash collisions, and thus be able to impersonate any secure website with a seemingly valid SSL certificate. This prediction appears to have come true, with the latest research suggesting that the cost of using cloud computing resources to find a SHA-1 hash collision is now in the region of $75k, or perhaps even only a week's use of the largest botnets.

The majority of SHA-1 signed SSL certificates issued for use on publicly-accessible websites within the past few months, and that are valid beyond the start of 2017, were issued to hostnames under the .mil sponsored top-level domain. This sTLD is used by agencies, services and divisions of the United States Department of Defense.

A U.S. Navy .mil website, which uses a SHA-1 signed certificate issued earlier this year.

A U.S. Navy .mil website, which also uses a SHA-1 signed certificate issued earlier this year.

Many other SHA-1 certificates used by .mil websites are valid beyond the start of 2017, which means that Google Chrome already regards them as affirmatively insecure, crossing out the padlock icon:

article-navyweak

The security of some of these sites is further undermined by their use of TLS 1.0 connections, even though most users' browsers are likely to support later versions. TLS 1.0 is now considered weak and obsolete, with some standards bodies such as the PCI SSC mandating that it should no longer be used in new applications, and that existing applications must migrate to TLS 1.1 or later by June 2016.

Obsolete TLS 1.0 connection used by a military remote access service.

Obsolete TLS 1.0 connection used by a military remote access service.

But disabling support for TLS 1.0 is not always feasible, particularly as some older browsers such as Internet Explorer 8 do not support TLS 1.1 and 1.2. If it is essential for a server to retain support for TLS 1.0 (in addition to later versions), then TLS Fallback SCSV must be used to prevent downgrade attacks against clients that support TLS 1.1 or later. This will ensure that modern browsers will always use acceptably secure versions of TLS, while only the older clients can possibly use the weak, obsolete TLS 1.0 cipher suites.

Several other U.S. military remote access services only support the obsolete TLS 1.0 protocol, including two used by the Defense Logistics Agency. Some other military sites, including one of the Navy's VPN services do support TLS 1.2, but with obsolete cipher suites. These particular sites all use SHA-1 signed certificates that do not expire until 2017, and so are regarded as "affirmatively insecure" by Chrome.

DoD PKI infrastructure

The Department of Defence PKI infrastructure relies on two root certificate authorities (DoD Root CA 2 and DoD Root CA 3), but these are not included in all browsers by default.

Windows and Linux users must explicitly install the DoD root certificates in order for the subscriber certificates to be validated and trusted by their browsers. But interestingly, the DoD roots are trusted on Apple platforms by default; this means that the DoD has the necessary third-party attestation for inclusion in the Apple Root Certificate Program, even though many of the subscriber certificates fail to conform to the Baseline Requirements for the issuance and management of publicly-trusted certificates.

The U.S. Government has faced numerous hurdles in being recognised as a publicly-trusted certificate authority. In 2009, the Federal Public Key Infrastructure Management Authority (US FPKI) requested for its Federal Common Policy Framework Certificate Authority (Common Policy CA) root certificate to be added to Firefox and other Mozilla products. Only subscriber certificates for .gov and .mil domains would have been trusted under this root, but the request was eventually put On Hold in May 2015. It was decided that US FPKI should be treated as a Super-CA, whose subordinate CAs must apply for inclusions themselves.

One of the arguments for accepting the US government as a publicly-trusted certificate authority was that it would avoid the need to purchase commercial certificates and thus save taxpayer dollars. One viable alternative might have been to use the free Let's Encrypt certificate authority, which became trusted by all major browsers this week. However, the cross-signed Let's Encrypt Authority X1 intermediate certificate uses the X509v3 Name Constraints field to explicitly disallow its use by .mil domains. No other top-level domains are precluded from using Let's Encrypt.

Many .mil sites recommend using the InstallRoot tool to simplify the installation and management of the DoD root certificates on Windows machines. This tool also installs several intermediate certificates, which the Department of Defense uses to directly sign the subscriber certificates.

article-installroot41

As an example, the subscriber certificate issued to cec.navfac.navy.mil was signed on 19 March 2015 by the DOD CA-27 intermediate, which is signed by the DoD Root CA 2 trusted root. This chain of trust allows the browser to verify that cec.navfac.navy.mil is a legitimate site operated by a Department of Defense agency, and that the connection is not being subjected to a man-in-the-middle attack.

article-chain

These intermediate certificates are also signed with the arguably weak SHA-1 algorithm. Whilst not the most likely way in which SHA-1 will initially fail — a chosen-prefix attack such as the one used on MD5 in the Flame malware is more likely — if any of these intermediate certificates were to be targeted to find a collision, it would be possible for an attacker to generate valid subscriber certificates for any domain. This would allow the attacker to convincingly impersonate U.S. military sites and carry out man-in-the-middle attacks against browsers that trust the DoD root certificates.

The DOD CA-27 intermediate certificate that was used to issue the subscriber certificate for cec.navfac.navy.mil is valid until September 2017 and has a SHA-1 signature.

The DOD CA-27 intermediate certificate that was used to issue the subscriber certificate for cec.navfac.navy.mil is valid until September 2017 and has a SHA-1 signature.

Chrome also warns users when intermediate certificates are signed with SHA-1.

Chrome also warns users when intermediate certificates are signed with SHA-1.

Although the DoD PKI infrastructure is not trusted by all browsers, it is nonetheless surprising to see it flouting some of the well-founded rules and recommendations that apply to publicly trusted certificates as well as recommendations made by NIST. Many of these guidelines are backed by valid security concerns – in particular, using SHA-1 for signature generation is now considered ill-advised, as any well-funded attacker can plausibly compromise the affected certificates.

The risk to the Department of Defense is further heightened by enemy goverments being the most likely sources of attack. The projected cost of attacking SHA-1 is unlikely to be prohibitive, and some governments may already be in a position to find a hash collision faster than the most organised criminals.

One million SSL certificates still using “insecure” SHA-1 algorithm

Nearly a million SSL certificates found in Netcraft's October SSL Survey were signed with the potentially vulnerable SHA-1 hashing algorithm, and some certificate authorities are continuing to issue more. Google Chrome already regards these certificates as insecure, resulting in more warning signals than if the sites had been served over a completely unencrypted HTTP connection.

The latest research, dubbed the SHAppening, shows that these warnings are well founded, projecting that a full SHA-1 collision could be found within 49-78 days on a 512-GPU cluster. Renting the equivalent processing time on Amazon's EC2 cloud computing service would cost only $75k-$120k, which is an order of magnitude less than earlier estimates. The researchers point out that this represents an important alarm signal, and that the industry's plans to move away from SHA-1 by 2017 might not be fast enough.

The researchers consider that is now feasible [pdf] for a well funded attacker to impersonate an SSL site that uses a publicly trusted SHA-1 certificate. Worse still, while browsers still accept SHA-1 signatures, SSL sites remain at risk even after migrating to SHA-2: if an attacker were to compromise an intermediate CA certificate signed with SHA-1, he could generate valid certificates for arbitrary domains.

The SHA-2 and SHA-3 family of cryptographic hash algorithms are now the only ones approved by the National Institute of Standards and Technology (NIST) for digital signature generation. Although the SHA-2 family includes SHA-224, only the stronger SHA-256, SHA-384 and SHA-512 algorithms are allowed by the CA/Browser Forum's Baseline Requirements for the issuance and management of publicly-trusted certificates.

These newer algorithms do not exhibit the mathematical weaknesses of SHA-1, and also generate longer digests than the 160-bits computed by SHA-1. Almost all new SHA-2 subscriber certificates use SHA-256 (99.99%), while only a handful use SHA-384 and SHA-512. Most of the latter are issued by DigiCert.

The rise of SHA-2

Migration to SHA-2 slowly gathered pace when the National Institute of Standards and Technology (NIST) banned the use of SHA-1 for new signature generation after the end of December 2013, but the rate of growth increased in the wake of the 2014 HeartBleed bug. This bug resulted in around half a million certificates being potentially compromised, requiring urgent reissuance and revocation. By this time, many certificate authorities were already using SHA-256 for new certificates, which in turn caused a significant boost in the number of SHA-2 certificates in use on the web.

SHA-1 vs SHA-2 (source: Netcraft SSL Survey October 2015)

SHA-1 vs SHA-2 (source: Netcraft SSL Survey October 2015)

SHA-2 eventually overtook SHA-1 in May 2015, but there are still nearly a million certificates currently using SHA-1.

The use of SHA-1 in new certificates is expected to halt by the close of this year, as from 2016, the CA/Browser Forum Baseline Requirements will forbid the issuance of any new subscriber certificates or subordinate certificates that use the SHA-1 algorithm.

However, with less than three months to go, Symantec proposed a motion (endorsed by Entrust, Microsoft and Trend Micro) to allow the issuance of SHA-1 signed certificates throughout 2016. The proposed changes to the Baseline Requirements would have catered for "a very small number of very large enterprise customers" who are unable to migrate to SHA-2 before the end of this year. But with the new cost projections making the risk of a real-world attack higher than previously believed, Symantec and the endorsers subsequently withdrew the ballot on 12 October.

Even if this ballot were accepted, many certificate authorities have already decided to avoid using SHA-1 because of the way some browsers will treat these certificates. For example, if an existing SHA-1 certificate is due to expire during 2016, Google Chrome currently flags this up as a weak security configuration and warns the user that their connection may not be private. Certificates that are valid until 2017 or later are treated as affirmatively insecure, with the "https" protocol crossed out.

Weak and insecure certificates

Despite being regarded as weak or insecure by one of the most commonly used browsers, over 120,000 of the SHA-1 certificates currently in use on the web were issued during 2015, and 3,900 of these have expiry dates beyond the start of 2017. The owners of these certificates will undoubtedly need to replace them months — or in some cases, years — before they are due to expire.

For example, Deloitte is still using a SHA-1 signed certificate that was issued in February 2015 and valid until 2020. Google Chrome already regards this certificate as insecure:

deloitte

This SHA-1 certificate was issued by A-Trust Gesellschaft für Sicherheitssysteme im elektronischen Datenverkehr GmbH, who operate the A-Trust-nQual-03 root certificate that is trusted by all mainstream browsers.

In February 2014, when Netcraft first published a look at SHA-2 migration, more than 256,000 SHA-1 signed certificates would have been valid beyond the start of 2017. Despite the browser vendors' deprecation plans, this total is roughly the same today.

Buggy browsers treating some SHA-2 certificates as insecure

Some certificate authorities were hit by an unexpected pitfall after migrating to SHA-2, after failing to use new names for their SHA-2 signed intermediate certificates. SSLMate, an SSL certificate vendor, published two examples of how Google Chrome could erroneously suggest that a site was affirmatively insecure for serving a SHA-1 certificate, even when the full certificate chain actually used the SHA-2 hashing algorithm. This undesirable behaviour was caused by caching in the cryptographic libraries used by Chrome (CryptoAPI on Windows, and NSS on Linux).

When a CA migrates to SHA-2, it can either reuse an existing intermediate certificate by re-signing the existing public key with SHA-2, or it can generate a new one with a new public key and subject name. If the existing certificate is reused, some Windows browsers will end up ignoring the chain provided by the server and instead use the old SHA-1 intermediate certificate if it has been cached previously. This will cause Chrome to believe that the connection to the site is affirmatively insecure.

SSLMate observed that StartCom was still issuing SHA-2 certificates that were signed by a SHA-1 intermediate, despite CA/Browser Forum Ballot 118 stating that CAs should not do this. Netcraft's SSL Survey also shows the same mistakes being made by other certificate authorities, including WoSign, Entrust and Unizeto amongst others. All of these certificates may be regarded as insecure by the Chrome browser.

The second example involved a bug in older versions of NSS on Linux, which could cause Chrome to use a cross-signed root even if a shorter and newer chain exists. If the cached cross-signed certificate uses SHA-1, Chrome will consider the chain to be weak, even though the server may have sent a chain that used SHA-2 throughout.

Fraudsters use paypal-office.com OV certificate for phishing

In June 2015, Trustwave issued an organisation-validated certificate for paypal-office.com, myaccount-paypal.com and paypal-sign.com that was used on a PayPal phishing site. The certificate was issued to an individual in India, Asha Shaikh, who may be the fraudster behind the phishing site, or perhaps one of the fraudster's victims. The phishing attack is now offline, but the certificate has yet to be revoked by Trustwave at the time of writing.

Rendered contents of phishing site found on www.paypal-office.com. The error message visible at the top of the page is a giveaway: the geo-location of the visitor's IP address failed, and it reveals the location of the files used to power the phishing site.

Certificate authorities typically sell certificates in three broad categories of assurance: domain-validated certificates simply validate control over a domain name; organisation-validated certificates include the identity of the organisation; and Extended Validation certificates increase the level of identity checking done to meet a recognised industry standard.

The difference between DV, OV, and EV certificates is sometimes subtle — many sources of consumer advice do not make the distinction between certificates that provide further identity information and those that only validate domain name ownership. For example, Google Chrome's help page states: "You can tell if a site is real if it has a valid TLS/SSL certificate".

Most certificates with deceptive domain names are domain-validated, though some appear to be organisation-validated. Many of the SSL certificates associated with CloudFlare's "Universal SSL" programme are ostensibly organisation-validated; however, the organisation being validated in this case is CloudFlare itself and not each individual customer.

paypal-office.com certificate

An organisation-validated certificate for paypal-office.com shown in the Windows certificate viewer.

Rather than be processed automatically, as is possible with domain-validated certificates, most higher-assurance certificate requests will be reviewed by a human prior to issuance. This additional level of validation makes it all the more surprising that a request for a certificate containing "paypal" wasn't considered a high risk request, and consequently rejected after being subjected to increased scrutiny.

Trustwave offers a Relying Party warranty with its certificates, covering fraudulent credit card charges made by a Trustwave certificate holder. However, the warranty does not cover other types of fraud, meaning phishing for credentials or fraudulent payments using other payment methods are not covered. As a result, victims of this phishing attack will not be able to claim on this warranty, despite having their PayPal credentials stolen by a fraudster using a Trustwave certificate.

Certificate authorities issue SSL certificates to fraudsters

In just one month, certificate authorities have issued hundreds of SSL certificates for deceptive domain names used in phishing attacks. SSL certificates lend an additional air of authenticity to phishing sites, causing the victims' browsers to display a padlock icon to indicate a secure connection. Despite industry requirements for increased vetting of high-risk requests, many fraudsters slip through the net, obtaining SSL certificates for domain names such as banskfamerica.com (issued by Comodo), ssl-paypai-inc.com (issued by Symantec), and paypwil.com (issued by GoDaddy).

CloudFlare, a content delivery network that provides free "Universal SSL" to its customers, is a hotspot for deceptive certificates, accounting for 40% of SSL certificates used by phishing attacks with deceptive domain names during August 2015. CloudFlare's Universal SSL certificates are provided in partnership with Comodo, and CloudFlare also use GlobalSign certificates for some of its customers. CloudFlare's flexible SSL option also appeals to fraudsters, offering a padlock in victims' browsers without the need for attackers to set up SSL on their web servers.

PayPal phishing site

A screenshot of a PayPal phishing site using a widely trusted SSL certificate valid for www.pay-pal.co.com. The certificate is a CloudFlare Universal SSL certificate issued by Comodo. The certificate has not been revoked; however, the phishing site is no longer available.

Websites that use TLS (the successor to SSL) are marketed as being trustworthy and operated by legitimate organisations. Consumers have been trained to "look for the padlock" in their browser before submitting sensitive information to websites, such as passwords and credit card numbers. While the reality is more nuanced, the data submitted to a phishing site using TLS is protected from eavesdroppers. However, a displayed padlock alone does not imply that a site using TLS can be trusted, or is operated by a legitimate organisation.

NatWest phishing site

A screenshot of a NatWest phishing site using a widely trusted SSL certificate valid for natwestnwolb.co.uk. (nwolb stands for NatWest online banking. The legitimate NatWest online banking service is available at www.nwolb.com.)

Bank of America phishing site

A screenshot of a Bank of America phishing site using a widely trusted SSL certificate valid for banskfamerica.com.

The following table lists some examples of deceptive SSL certificates that have been used to conduct phishing attacks, along with their Domain Registration Risk scores:

Hostname Phishing Target Certificate Authority Assurance Risk Score Revoked
halifaxonline-uk.com Halifax GlobalSign (CloudFlare) OV* 10.0 No
emergencypaypal.net PayPal Comodo (CloudFlare) OV* 9.17 Yes
blockchaín.info (xn--blockchan-n5a.info) Blockchain GlobalSign (CloudFlare) OV* 8.52 No
blockachain.info Blockchain Comodo DV 8.42 No
itunes-security.net Apple iTunes Symantec DV 8.08 No
phypal.com PayPal Symantec DV 6.61 No
btintranert.com BT GoDaddy DV 5.56 Yes

* The certificates that CloudFlare issues to its customers are ostensibly organisation-validated, as they contain CloudFlare's company name and address. However, the customer domains themselves are only domain-validated.

The CA/Browser Forum's Baseline Requirements – a set of rules that publicly-trusted certificate authorities are expected to follow – require that high-risk domain names that may be used for fraud or phishing are subjected to additional verification:

High Risk Certificate Request: A Request that the CA flags for additional scrutiny by reference to internal criteria and databases maintained by the CA, which may include names at higher risk for phishing or other fraudulent usage.
The CA SHALL develop, maintain, and implement documented procedures that identify and require additional verification activity for High Risk Certificate Requests prior to the Certificate’s approval.

Despite this requirement, many major certificate authorities issue SSL certificates for deceptive domains used in phishing attacks. Notable exceptions include DigiCert and Entrust, neither of which issue domain-validated certificates.

A pie chart showing SSL certificates containing a deceptive domain name that were used in phishing attacks during August 2015, split by certificate authority. CloudFlare and non-CloudFlare certificates are shown separately.

Certificate authorities commonly provide SSL certificates at three different levels of assurance:

  • Domain validated (DV)
    Certificate authorities only have to check that the certificate's applicant controls the domain name contained in a DV certificate. These certificates are typically the cheapest option, and can be had for free or be purchased for less than $10. Let's Encrypt is planning to offer free, automatically-issued DV certificates starting later in 2015.
  • Organisation validated (OV)
    In addition to validating the domain name in the certificate, the identity of the person or organisation applying for an OV certificate is also verified by the certificate authority and included in the certificate. Most browsers do not treat OV certificates any differently to DV certificates.
  • Extended validation (EV)
    Like OV certificates, the identity of the organisation applying for an EV certificate is verified by the certificate authority. However, the verification is more stringent. EV certificates also receive different treatment in major web browsers – the address bar is either partially or completely coloured green and the requesting organisation's name and country are displayed next to the padlock. The requirements for EV certificates in Chrome are changing, with many certificate authorities caught out by recent changes to require Certificate Transparency.

The requirement to perform additional verification of high risk certificate requests applies to all levels of assurance. However, DV certificates are often issued completely automatically within minutes, making it easy for fraudsters to obtain DV certificates for deceptive domain names.

Several certificate authorities offer free trial certificates with shorter validity periods. For example, Comodo offers free 90 day certificates, which have been used by a number of SSL phishing attacks. Symantec also offers free 30 day certificates through its GeoTrust brand. The short validity periods are ideal for fraudsters as phishing attacks themselves typically have short lifetimes.

Netcraft's Domain Registration Risk service automatically identifies deceptive domain names constructed using such tricks. The service calculates a risk score between 0 (low risk) and 10 (high risk) for each domain name, which represents the likelihood that the domain name will be used to carry out a phishing attack. Certificate authorities can make use of the service to determine if a domain name is likely to be used for fraudulent purposes before issuing the certificate.

The service can be provided as an API that mimics a Certificate Transparency log server for ease of integration with your existing certificate issuance process. The same API can also be used with Netcraft's certificate compliance checking service, which can identify certificates before they are issued that do not conform with the CA/B Forum's Baseline Requirements or its EV Guidelines.

eBay phishing sites hosted by… eBay

Fraudsters are stealing eBay usernames and passwords using phishing pages hosted on eBay's own infrastructure. One of these pages, targeting German users, is shown below:

An eBay phishing form hosted on eBay's own infrastructure. The form contents are submitted to an external domain in Russia.

An eBay phishing form hosted on eBay's own infrastructure. The form contents are submitted to an external domain in Russia.

The convincing appearance of the spoof login form is bolstered by the fact that it is hosted on a genuine eBay domain, ebaydesc.com. This domain is ordinarily used to host descriptions for eBay listings which are displayed within iframes on eBay listing pages.

In this case, the corresponding eBay listing has already been deleted, although the phishing content within the listing's description can still be viewed by browsing directly to the relevant URL on vi.vipr.ebaydesc.com. Consequently, the attack is still live and capable of stealing credentials from eBay users.

The URL of the credential-stealing script is only momentarily visible in the address bar before the victim is redirected to the genuine eBay site.

The URL of the credential-stealing script is only momentarily visible in the address bar before the victim is redirected to the genuine eBay site.

When a victim enters his username and password into the form, both values are submitted to a PHP script hosted on a server in Russia. After stealing the credentials, this script then redirects the victim to the genuine ebay.de login page, which reports that the username or password was incorrect.

After the victim's credentials are stolen, he is redirected to the real eBay login page. Note that the username field has been automatically populated with the username stolen by the fraudster.

After the victim's credentials are stolen, he is redirected to the real eBay login page. Note that the username field has been automatically populated with the username stolen by the fraudster.

This error message might cause the victim to become suspicious enough to look at the browser's address bar, to check he is on the right website; but it will already be too late at this point – his credentials will have already been stolen, and because his browser will now be showing ebay.de in the address bar, he may not even realise that his credentials have just been sent to a web server in Russia. There is consequently little chance of the victim reacting by changing his password, allowing the fraudster to take full advantage of the stolen credentials at his leisure.

The website involved in collecting the stolen credentials has also been used to host other phishing attacks targeting German-speaking consumers, including sites impersonating PayPal, Apple, and mobile.de.

In an attempt to evade detection by eBay and others, the fraudster has obfuscated the HTML source of his eBay phishing form. This makes it impossible to find such a listing by searching for any of the words that appear in the description, yet the rendered results appear as normal when viewed in a web browser.

The obfuscated HTML source used by the phishing content hosted by eBay.

The obfuscated HTML source used by the phishing content hosted by eBay.

Allowing anyone to insert arbitrary HTML and malicious scripts into a listing's description gives plentiful opportunities to would-be fraudsters, particularly as this weakness has been exploited to carry out similar attacks against eBay users in the past. Last year, Netcraft reported on fraudsters injecting malicious JavaScript into eBay listings to set up man-in-the-middle attacks against car buyers, and similar JavaScript redirection techniques have continued to be exploited throughout 2015.

These phishing methods can be much more successful than traditional phishing attacks (where content is hosted solely on an unrelated domain). The techniques employed in these latest attacks are not permitted under eBay's HTML and JavaScript policy; however, a fraudster intent on stealing passwords is not going to be deterred by words alone.

Thousands short-changed by EV certificates that don’t display correctly in Chrome

Certificate authorities have sold thousands of Extended Validation (EV) certificates that do not display correctly in Google Chrome. Over 10,000 EV certificates (5% of all EV certificates) fail to receive the green EV indicator in the latest desktop version of Google Chrome.

Certificate authorities market EV, and justify its cost, by highlighting the increased trust instilled by the green bar containing the company's name. Without the green EV bar, visitors will struggle to distinguish a $1,000 EV certificate from a $10 domain-validated certificate.

The lack of EV indicator for these certificates reflects Google's policy requiring EV certificates to be delivered with Certificate Transparency information. Up to half of an affected site's visitors may be affected, given Chrome's significant market share. Most CAs have sold this type of flawed EV certificate; however, the extent to which each CA's certificates are affected varies significantly.

chrome-vs-firefox

The Lloyds Bank login page, as viewed in Chrome 44 (above) and Firefox (below). The SSL certificate, issued by Symantec in June 2015, fails to receive the green EV indicator in Chrome.

Advertising

Certificate marketing page advertising the "green bar" indication.

Certificate marketing page advertising the "green bar" indication.

Almost universally, CAs advertise their EV products as (unconditionally) triggering browsers' green bars:

Such advertising underlines one of the primary reasons to purchase an EV certificate over a cheaper option — the green bar that is visible in the address bar.

This additional assurance comes at a price: EV certificates command a significant premium over the cheapest type of certificate. For example, Symantec's EV certificates cost $995 per year, almost $600 more than its cheapest directly advertised option. If you include its other brands, a Symantec DV certificate can be had for $10.95 per year.

Extended Validation

PayPal's EV certificate in Google Chrome

PayPal's EV certificate in Google Chrome. The address bar features a green indicator, and also displays the company name and location (highlighted in red). The presence of valid Certificate Transparency information is indicated (highlighted in blue).

The guidelines for issuing Extended Validation certificates were first published by the CA/Browser Forum in June 2007, motivated by the lack of a well-defined standard for high-assurance identity verification. As well as validating control over the requested domain names, CAs identify the requesting organisation. Major browsers typically display the validated organisation's name in a green box in the address bar. The cheapest type of certificate, domain-validated, does not include this additional information and does not trigger the green box.

Merely issuing a certificate following the EV guidelines is not sufficient for the certificate to trigger the browser's special treatment: the CA's root certificate must be embedded in the browser; the CA must be specifically approved to issue EV certificates; and the certificate must conform to any additional policies set by the browser. Certificate authorities are periodically audited against these requirements, and are required to publish audit statements, though many audited CAs still issue non-compliant certificates.

All major browser vendors are members of the CA/Browser Forum that defines the EV guidelines, and most maintain an independent CA inclusion policy that can be more or less strict than the published minimum requirements. For example, Mozilla, Google, Microsoft, and Apple maintain separate EV policies and CAs must apply to each individually to obtain EV treatment in their browser.

Certificate Transparency

Google has recently added the additional condition that in order to be treated as EV in Chrome, the certificate must be present in a Certificate Transparency log and be bundled with a timestamp (an SCT) signed by the log. This policy for EV certificates is intended to be a trial run for requiring Certificate Transparency for all certificates.

Certificate Transparency is motivated by incidents like DigiNotar, mis-issuance from CNNIC, TURKTRUST, ANSSI, and TrustWave's issuance of a MiTM certificate. By requiring newly issued certificates to be logged in publicly-auditable databases, Google hopes to make it easy to monitor domains for rogue certificates, and to enable regular and post-incident analysis of CA issuance practices.

The signed timestamps (SCTs) can be delivered to the browser in three ways: embedded in the certificate itself, delivered via a stapled OCSP response, or included in a custom TLS extension by the web server. Only the first option is currently practical according to Google as it does not require the certificate holder to update their server software. The second option requires support from the CA in its OCSP responder software, and the client must enable OCSP stapling. Almost three-quarters of all SSL certificates were delivered without a stapled OCSP response in the August 2015 Netcraft SSL Server Survey. The TLS extension, on the other hand, does not require CA support at all, but server-side support is not yet widely available.

Chrome's policy only applies to EV certificates issued after 1st January 2015. At the start of 2015, Google produced a whitelist of existing EV certificates: certificates were included if they were present in at least one qualifying CT log and didn’t otherwise already comply. EV certificates that are not included in the whitelist must comply with the new policy. While it is possible for pre-2015 non-whitelisted certificates to comply — using a stapled OCSP response or in the TLS extension — it is not trivial to configure.

Netcraft's Site Report tool can be used to inspect the SCTs (if any) presented by a given website and whether or not the certificate is present in Google's whitelist.

Widespread failures

ev-ct-per-ca-2

DigiCert includes its recently acquired roots that previously belonged to Verizon Business.

Many CAs have issued EV certificates that do not meet Google's requirements, which has resulted in over 10,000 certificates not receiving the EV indicator in the current version of Chrome. Of these certificates, 42% were issued after 1st January 2015, whilst the remaining 58% were issued pre-2015 but are missing from the whitelist and do not otherwise qualify.

Chrome's Address Bar EV Notes
Yes Normal EV display in Google Chrome
No Normal non-EV display in Google Chrome

Expected behaviour for SSL certificate display in Google Chrome's address bar.

Certificate Authority Chrome's Address Bar EV Issued Notes
Symantec Yes Jun 29 2015 No SCTs received
DigiCert (Verizon) Yes Mar 16 2015 No SCTs received
DigiCert Yes Aug 22 2014 Not in Google's whitelist
GoDaddy Yes Jun 25 2015 Too few SCTs for validity period
Entrust Yes Apr 10 2015 Malformed signatures in SCTs
GlobalSign Yes Feb 24 2015 No SCTs received
StartCom Yes Jun 29 2015 No SCTs received
WoSign Yes Jul 6 2015 No SCTs received

Actual behaviour of SSL certificate display in Google Chrome's address bar.
†This certificate should have been included on the whitelist; however, a bug in Google's whitelist meant it was incorrectly excluded.

hhhh

A GlobalSign certificate that despite having undergone EV validation, fails to trigger the green bar in Chrome.

Whilst most CAs have issued at least some EV certificates with embedded SCTs, others have not embraced Certificate Transparency at all.

WoSign has never issued an EV certificate that contains embedded SCTs and it does not support the second-most-prevalent method for delivering SCTs — via its OCSP responses. This is also the case for StartCom, where almost 100% of EV certificates issued by StartCom so far in 2015 fail to receive EV treatment in Chrome. Some StartCom EV certificates are receiving the EV indicator as a result of Google's one-off whitelist, and a single post-2015 certificate is being used on a server that supports sending SCTs via the TLS extension. WoSign and StartCom are not alone, however, as several other CAs have issued EV certificates without embeddeding SCTs, including Certplus (OpenTrust/KEYNECTIS).

Although Google produced a whitelist of existing EV certificates at the start of 2015, a significant number of pre-2015 certificates lost their EV treatment after Google Chrome started enforcing its CT policy. CAs had the opportunity to inspect Google's draft whitelist; however, many certificates were not submitted to a CT log in time. As well as omissions by the CAs, there were also errors in the mechanism used by Google to generate the whitelist.

The second type of failure to be included in the whitelist, bugs in Google's implementation, can be demonstrated by examining a DigiCert certificate (serial number 0ae01c52bf4917b4527c20bae5e2cd82): it is present in at least one Google CT log with a timestamp indicating it was first logged on 28th August 2014:

Log: https://ct.googleapis.com/pilot
Entry ID: 4867084
Timestamp: 2014-08-28 11:56:54 GMT
Certificate Serial Number: 0ae01c52bf4917b4527c20bae5e2cd82

Despite being logged in accordance with Google's policies, it does not appear in Google's whitelist. In this case, a bug in Google's whitelisting code meant it was incorrectly excluded.

Some CAs offer the option to their customers to not include SCTs in their EV certificates, where inclusion in a public log would leak DNS names the customer would rather keep private. However, all of the certificates in this analysis were found on public-facing HTTPS services by Netcraft's SSL survey, or were included in CT logs.

Google's latest policy update in May 2015 could mean that 7,000 more EV certificates will lose the green bar treatment in Chrome. Certificates must now be delivered with SCTs from independent logs — i.e. at least one Google log and one non-Google log. Certificates that do not meet this new requirement still receive the green bar in Chrome, but are anticipated to stop working when Chrome's code catches up with the new policy. It is not clear whether certificates issued before the policy update will be whitelisted or subjected to the new policy.

Comodo is the CA most affected by the May 2015 policy update, with almost 6,000 EV certificates at risk if Google's new policy is applied from 1st Jan 2015. Comodo has recently issued certificates with SCTs from too few independent logs: for example, Comodo issued a certificate on 3rd August 2015 that is missing a non-Google SCT.

Before they were eventually deployed in March 2015, CAs had known for over a year that the changes to Chrome's EV behaviour were coming. Google's intention was for CAs to ensure that all issued certificates were meeting the requirements before the effective date. This was not the case for most CAs, however, and many non-compliant certificates remain in existence now that Chrome is enforcing the requirements. Worse still, many CAs are continuing to sell EV certificates that will not receive the indicator in Chrome.

Identifying non-compliant certificates

Using data from its SSL Survey, Netcraft's certificate compliance checking service can promptly identify, and bring to the attention of CAs, all kinds of non-compliant certificates, including those that are not receiving the EV indicator in Chrome. The service also identifies certificates that will stop receiving the EV indicator as soon as Google's May 2015 policy update becomes effective. By using Netcraft's service to identify these certificates, CAs will be in a position to re-issue them such that they should once again receive the green EV indicator.

Netcraft's service can also be used by CAs to test their certificates for compliance issues before issuance, by submitting pre-certificates or certificates to Netcraft and only releasing to customers those that are found to be fully compliant. Non-compliant certificates can then be revoked without ever being deployed.