On the surface, Nokia's proxy-based Xpress Web browser — available for the manufacturer's Asha and flagship Lumia handsets — sounds nothing short of excellent, routing Internet traffic through Nokia's servers in order to compress data and eliminate precious bits that would otherwise count toward your cellular data cap. So far so good, right? Now for the bad part. As part of the process, Nokia's servers temporarily decrypt all HTTPS data sent its way — without clearly informing end users of the fact.
Websites often use HTTPS to secure sensitive information such as payment details and other intensely personal tidbits. Security researcher Gaurang Pandya first discovered the issue, which is essentially a man-in-the-middle attack — but, Nokia claims, a benign one. The company released a statement to GigaOm admitting that, yes, Nokia's Xpress Browser servers do decrypt HTTPS-encrypted data in order to compress it, but no, Nokia doesn't look at the unprotected information.
Importantly, the proxy servers do not store the content of web pages visited by our users or any information they enter into them. When temporary decryption of HTTPS connections is required on our proxy servers, to transform and deliver users’ content, it is done in a secure manner... Nokia has implemented appropriate organizational and technical measures to prevent access to private information. Claims that we would access complete unencrypted information are inaccurate.
Basically, you have to trust Nokia's word and non-described security procedures if you plan to continue using the Xpress Browser to send HTTPS traffic. A couple of Nokia's actions in this ordeal come off as a bit questionable, however, even if there is no reason to believe Nokia is snooping on your Web traffic.
First, the company didn't disclose the privacy-busting decryption in a straightforward way to its customers — a security researcher had to discover the procedure. Secondly, Pandya points out that Nokia configured the browser to automatically trust the security certificates issued by Nokia, which stops the Xpress browser from warning you about the HTTPS hijacking. In other words, the company's circumventing a security procedure designed to inform people that the server they're communicating with isn't the server they think they're communicating with. That shatters the protection HTTPS is supposed to provide, and Nokia breaks that trust without clearly warning users up-front.
By comparison, other mobile browsers that offer data compression handle things a little differently. Opera Mini clearly states that it decrypts HTTPS traffic in its FAQ, whereas Amazon's Silk browser doesn't decrypt HTTPS traffic whatsoever. The Silk browser also doesn't compress HTTPS traffic as a result, however. The bigger issue here isn't so much what Nokia is doing, so much as how the company is doing it.