Ninety percent of the Internet's top 200,000 HTTPS-enabled websites are vulnerable to known types of SSL (Secure Sockets Layer) attack, according to a report released Thursday by the Trustworthy Internet Movement (TIM), a nonprofit organization dedicated to solving Internet security, privacy and reliability problems.

The report is based on data from a new TIM project called SSL Pulse, which uses automated scanning technology developed by security vendor Qualys, to analyze the strength of HTTPS implementations on websites listed in the top one million published by Web analytics firm Alexa.

SSL Pulse checks what protocols are supported by the HTTPS-enabled websites (SSL 2.0, SSL 3.0, TLS 1.0, TLS 1.1, etc.), the key length used for securing communications (512 bits, 1024 bits, 2048 bits, etc.) and the strength of the supported ciphers (256 bits, 128 bits or lower).

An algorithm is used to interpret the scan results and assign a score between 0 and 100 to each HTTPS configuration. The score is then translated into a grade, with A being the highest (over 80 points).

Half of the almost 200,000 websites in Alexa's top one million that support HTTPS received an A for the quality of their configurations. This means that they use a combination of modern protocols, strong ciphers and long keys.

Despite this, only 10 percent of the scanned websites were deemed truly secure. Seventy-five percent -- around 148,000 -- were found to be vulnerable to an attack known as BEAST, which can be used to decrypt authentication tokens and cookies from HTTPS requests.

The BEAST attack was demonstrated by security researchers Juliano Rizzo and Thai Duong at the ekoparty security conference in Buenos Aires, Argentina, in September 2011. It is a practical implementation of an older theoretical attack and affects SSL/TLS block ciphers, like AES or Triple-DES.

The attack was fixed in version 1.1 of the Transport Layer Security (TLS) protocol, but a lot of servers continue to support older and vulnerable protocols, like SSL 3.0, for backward compatibility reasons. Such servers are vulnerable to so-called SSL downgrade attacks in which they can be tricked to use vulnerable versions of SSL/TLS even when the targeted clients support secure versions.

The easiest way to mitigate the BEAST attack on the server side is to prioritize the RC4 cipher for HTTPS connections, said Ivan Ristic, director of engineering at Qualys, via email. RC4 is a stream cipher and is not vulnerable to this attack.

In addition to supporting multiple protocols, many HTTPS-enabled servers also support multiple ciphers in order to ensure compatibility with a variety of clients. A special setting can be used on the server to specify the order in which the ciphers should be used and to prioritize RC4.

"I believe that most administrators are not aware of the need to perform this task," Ristic said.

Protections against the BEAST attack have already been built into newer browsers. However, there are a lot of people, especially in business environments, who use old browsers like Internet Explorer 6, which are still vulnerable, Ristic said.

SSL Pulse scans also revealed that over 13 percent of the 200,000 HTTPS-enabled websites support the insecure renegotiation of SSL connections. This can lead to man-in-the-middle attacks that compromise SSL-protected communications between users and the vulnerable servers.

"For your average Web site -- which will not have anything of substantial value -- the risk is probably very small," Ristic said. "However, for sites that either have a very large number of users that can be exploited in some way, or high-value sites (e.g., financial institutions), the risks are potentially very big."

Fixing the insecure renegotiation vulnerability is fairly easy and only requires applying a patch, Ristic said.

TIM plans to perform new SSL Pulse scans and to update the statistics on a monthly basis in order to track what progress websites are making with their SSL implementations.

This is part of a larger TIM project that will focus on SSL implementation and governance issues. The organization also announced the creation of an SSL Internet Taskforce on Thursday, to develop and propose solutions for known problems in these key areas.

The taskforce members include Michael Barrett, chief information security officer at PayPal; Taher Elgamal, one of the creators of the SSL protocol; Adam Langley, a Google software engineer responsible for SSL in Chrome and on the company's front-end servers; Moxie Marlinspike, the creator of the Convergence project, which offers an alternative method for SSL certificate validation; Ivan Ristic, the creator of the Qualys SSL Labs and Ryan Hurst, chief technology officer at certificate authority GlobalSign.