In 2024, the IETF, via its MASQUE working group, introduced a new mechanism — Scramble Transform — to augment traffic protection for IP packets transmitted over the Quick UDP Internet Connections (QUIC) protocol. Scramble Transform is an obfuscation method applied to handshake and application packet headers, where visible plaintext information is ‘scrambled’ into replacement text that remains readable but meaningless. Scramble Transform is implemented by applying a formula that combines an obfuscation algorithm, a salt value, and a mask value. The mechanism affects fields such as Destination Connection ID (DCID), Source Connection ID (SCID), Packet Type, Key Phase Bit, Spin Bit, and Retry Token.

Why Scramble Transform matters

While Scramble Transform adds another layer of protection against unauthorized third parties attempting to steal traffic information, it also makes legitimate traffic monitoring and security enforcement more difficult. Analysis and categorization of traffic for these purposes often rely on techniques that match packet, flow and application patterns and behaviors. The progressive loss of visible traffic data challenges these techniques, increasing overhead and management complexities.

To give an example, the absence of DCID and SCID information can make it difficult to identify the servers that are handling user requests, especially when IP address information is constantly changing. Similarly, not knowing whether a packet is an application packet or a handshake packet complicates the granular analysis of traffic flows. In the case of the Key Phase Bit, networking tools that previously derived application identities by observing application-specific encryption patterns no longer have sufficient data to establish such connections. Likewise, scrambling the Spin Bit information hides unique toggling behaviors which could be used to calculate passive RTT values or packet pacing, removing a vital input used to measure application behavior and network responsiveness. Another field scrambled under the new IETF recommendation is the Retry Token. This token is created by a server to validate a client device. Scrambling the token prevents networking tools from identifying reused tokens.

How does Scramble Transform affect network policies and actions?

Losing more pieces of the information puzzle disrupts the implementation of network policies. Traffic-aware policies, such as priority routing, compression and intelligent load balancing, can no longer be applied to QUIC traffic. The loss of spin bit information, for instance, compromises RTT readings, which are often used to analyze traffic speeds, latency, and jitter. As such , timely detection of service quality degradation across applications such as video streaming becomes impossible. Meanwhile, issues such as congestion, malfunctioning devices, and bandwidth-hogging applications will remain unaddressed.

With Scramble Transform, security functions such as firewalls and intrusion prevention systems can no longer detect network cues – for example, the abnormal use of CIDs which can indicate session hijacking, or unusual token usage patterns that can suggest DoS amplification attacks. Similarly, not being able to distinguish handshake packets from application packets increases the probability of malicious activities such as protocol fingerprinting, which uses obscure versions of QUIC, and replay attacks that manipulate 0-RTT configurations. Even common attacks such as DDoS take longer to detect as the usual handshake communication data is not readily distinguishable from regular application flows.

In parallel, losing Key Phase bit information creates a ripe opportunity for threat actors to launch replay attacks or tamper with traffic flows, as updates to the encryption keys no longer appear on typical monitoring radars. Likewise, modifications to spin bit information become undetectable, enabling threat actors to freely exfiltrate information using methods such as RTT-based signaling. In the case of retry tokens , obscuring token information by scrambling it makes it harder for security detection tools to identify tokens that have already been used or to detect if someone is launching a series of fake tokens. As a result, servers might end up establishing connections with illegitimate clients.

Reinstating visibility for ‘scrambled’ packets with next-gen DPI technology from ipoque  

Thanks to the cutting-edge DPI technology of ipoque, networking and cybersecurity vendors can continue to detect QUIC traffic despite the new Scramble Transform feature. Yes, you heard that right. In a recent test conducted by our team this year, both of our DPI engines – R&S®PACE 2 and R&S®vPACE proved capable of reliably detecting applications such as Google Meet, YouTube, and Facebook, despite this implementation.

How do we achieve this? We deploy encrypted traffic intelligence (ETI), which enables vendors to dig deeper into flows that are encrypted, obfuscated or anonymized. By leveraging machine learning techniques (e.g. KNN, Decision Trees) and deep learning techniques (e.g. CNNs, RNNs, LSTMs), as well as advanced caching and high-dimensional data analysis, ETI accurately identifies TLS-encrypted QUIC traffic flows, despite the newly introduced Scramble Transform. The DPI technology by ipoque not only identifies QUIC traffic by applications, protocols and service types, it also cuts through other layers of encryption and obfuscation techniques used in conjunction with QUIC – for example, DNS-over-QUIC, ECH, domain fronting, protocol mimicry, and IP truncation. It also reinstates transparency into QUIC traffic delivered via CDNs and VPNs.

Why is next-gen DPI important in the QUIC era?

The integration of next-gen DPI technologies into networking and cybersecurity solutions enables vendors to address the growing adoption of QUIC, which makes up 8.5   %  of all websites¹ today. As data security and privacy requirements (e.g., GDPR, HIPAA, and PCI-DSS) continue to grow, so will the need to replace legacy visibility solutions with advanced traffic intelligence tools such as next-gen DPI. This move not only circumvents the growing blind spots that hinder real-time intelligent responses to network events as the adoption of QUIC intensifies, but also future-proofs networking and cybersecurity solutions against a fully encrypted world.

Curious about how next-gen DPI technology can improve your visibility into QUIC traffic? Our experts are here to help you navigate the complexities of modern network challenges.

Sources:

[1] W3techs - https://w3techs.com/technologies/details/ce-quic