Digital key Credit: IDGNS
Millions of Web users could be left unable to access websites over the HTTPS protocol if those websites only use digital certificates signed with the SHA-2 hashing algorithm.
The warning comes from Facebook and CloudFlare as browser makers are considering an accelerated retirement of the older and increasingly vulnerable SHA-1 function.
The two companies have put mechanisms in place to serve SHA-1 certificates from their websites to old browsers and operating systems that don't support SHA-2, but are still widely used in some regions of the world.
These include Windows versions older than Windows XP with Service Pack 3, Android versions older than 2.3 (Gingerbread) and any applications that rely on OpenSSL 0.9.8 for encrypted communications.
SHA-1 (Secure Hash Algorithm 1) dates back to 1995 and became the default choice for signing SSL/TLS certificates after researchers proved in 2008 that certificates signed with the older MD5 function could be forged.
SHA-1 itself is also theoretically vulnerable, but the practicability of attacks against it is dependent on the computing power available. In 2012, renowned cryptographer Bruce Schneier estimated that a practical attack against SHA-1 would cost $700,000 using commercial cloud computing services by 2015 and $173,000 by 2018, putting it well within the reach of criminal syndicates.
As a result, the CA/Browser Forum, a group of certificate authorities and browser makers that sets guidelines for the issuance and use of digital certificates, decided that new SHA-1-signed certificates should not be issued after Jan. 1, 2016. Browser makers also decided that existing SHA-1 certificates will no longer be trusted in their software starting Jan. 1, 2017, even if they're technically set to expire after that date.
However, in October, a group of researchers presented a new way to break SHA-1 that is expected to lower the cost of attacks more quickly than previously anticipated. This has caused some browser makers like Mozilla and Microsoft to consider an even earlier cut-off date for SHA-1 certificates in their products.
To avoid users being unable to access their online properties, the owners of HTTPS websites that still use SHA-1 certificates -- about a million of them including around a sixth of the top 140,000 by traffic -- are under pressure to get new certificates signed with SHA-2.
The problem though, researchers from CloudFlare have pointed out, is that around 1.69 percent of users who currently access HTTPS-enabled services do so from browsers or operating systems that don't support SHA-2.
That might not seem much, percentage-wise, but it's actually over 37 million people and the majority of them are located in some of the "poorest, most repressive, and most war-torn countries in the world," CloudFlare's CEO Matthew Prince said Wednesday in a blog post.
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