Cisco Adds Encrypted Traffic Analysis Function

After months of field trials, Cisco now has moved to general availability its Encrypted Traffic Analytics (ETA) technology that addresses the increasingly critical security challenge of inspecting encrypted traffic for malicious activity - without first having to decrypt it.

In addition to its campus switches, ETA will also now be available with a majority of Cisco's enterprise routing platforms including its branch office router, Integrated Services Router, and Cloud Services Routers, the company announced Jan 10.

Attackers have increasingly begun using encryption to hide payloads, command and control communications, data exfilitration, and other activity from conventional malware detection tools. The only way to inspect this traffic typically is to decrypt it first, which besides being technologically challenging can compromise the privacy of the encrypted traffic — a problem especially for organizations that are required to comply with certain data regulations. The US-CERT has even cautioned organizations about the dangers of implementing interception tools that weaken TLS security.

"The network is growing more and more opaque through encrypted transports," says Cisco principal engineer TK Keanini. "When threat actors use encrypted transports their activities are hidden and we cannot afford for any malicious activity to be hidden, as this is the primary way they will persist in your network. "

A study conduced by Zscaler showed malicious threats using SSL encryption doubling in the first six months of last year. The security vendor reported blocking an average of 12,000 phishing attempts delivered over SSL/TLS every day — a 400% increase over the previous year.  

Many of the new malware strains that the company blocked last year used SSL to encrypt C&C communications. Banking Trojans such as Dridex and Trickbot accounted for 60% of these payloads and ransomware accounted of 25% of the payloads using SSL/TLS encryption for C&C activity.

"Seventy percent of the traffic that we are seeing in the Zscaler cloud is encrypted," says Deepen Desai, Zscaler's director of research and operations. "And 54% of the advanced threats Zscaler blocks are hidden inside SSL traffic, making clear that inspecting SSL traffic is no longer optional."

Cisco's ETA is designed to give organizations a way to detect and block such threats. ETA's principal benefit, according to Cisco, is that it does not rely solely on decryption to inspect traffic.

Instead, the technique uses a combination of network telemetry and machine learning to look for differences between malicious and benign traffic in three specific features of encrypted data.

The first is the initial data packet of the connection, which often can contain important data about the rest of the encrypted content. Then it looks at the sequence of packet lengths and times for clues into traffic content that go beyond what is available in the initial packet. The third feature that ETA checks, is the byte distribution across the packet payloads within the encrypted traffic flow, according to the company.  ETA's ability to spot the telltale signs of malware in encrypted traffic is based on research the company conducted into understanding the differences in how malicious and benign traffic uses TLS, DNS, and HTTP.

"Encrypted Traffic Analytics not only finds malicious activities without decryption but it also helps organizations answer a critical question on a daily basis: How much of my digital business travels in the clear versus encrypted?" Keanini says.  The Cisco network itself is able deliver the needed telemetry for security thereby lowering administrative and operational costs, he says.

The essence of ETA is its ability to infer things from encrypted traffic, by passively monitoring it, rather than opening up and inspecting the contents. "Decryption is not a real option for many reasons," Keanini says. "We need to respect encryption and privacy while finding other methods to detect through inference not direct inspection."

According to Keanini, enterprises that have been testing ETA have reported gaining additional insight into what is encrypted on their network and the quality of that encryption as well.

The broader support for ETA announced this week means that enterprises can now get visibility into more of the encrypted traffic flowing across their networks. "All of these infrastructure software upgrades get you to a point where there is new telemetry being analyzed by Cisco Stealthwatch without the needs for decryption," Keanini says.

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