Transparent TCP Proxy for SYN Flood Mitigation
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Solution Overview
Problem
Current TCP protocols are vulnerable to SYN flood attacks, which lead to high interrupt rates and CPU starvation due to incomplete TCP connections, and IP address management challenges, including synchronization issues and abuse potential in whitelisting/blacklisting approaches.
Innovation Solution
A transparent TCP proxy intercepts and translates TCP packets between clients and servers, establishing fully formed connections to prevent SYN flood attacks and authenticates initiators using cryptographic hash functions to ensure legitimate connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the server maintains state for all half-open connections to ensure reliable TCP connection establishment, then connection reliability is improved, but memory resources are consumed and the state table may overflow during SYN flood attacks
Solution Approach 1:
The patent extracts the state maintenance function from the attacked server and relocates it to a protective proxy server. The proxy server intercepts SYN packets, maintains the state table for half-open connections, and only forwards connections that complete the full TCP handshake to the actual server. This extraction prevents the original server from consuming memory resources during SYN flood attacks while maintaining connection establishment reliability.
Solution Approach 2:
The patent introduces a protective proxy server as an intermediary between the client and the attacked server. This intermediary intercepts TCP packets, validates complete connection handshakes, and filters out incomplete SYN packets before they reach the server. The intermediary maintains the state table and uses cryptographic verification to distinguish legitimate connections from flood attacks, thereby protecting the server's memory resources.
2Measurement precision
If the server processes each incoming SYN packet to maintain connection state, then connection tracking accuracy is improved, but CPU interrupt rate increases during SYN flood attacks
Solution Approach 1:
The patent extracts the CPU-intensive connection state tracking function from the attacked server and relocates it to a protective proxy server positioned in front of the server. The proxy server handles all SYN packet processing, state maintenance, and cryptographic verification, preventing high interrupt rates from reaching the original server while maintaining accurate connection tracking.
Solution Approach 2:
The patent introduces a protective proxy server as an intermediary that absorbs the CPU load from processing SYN packets. The intermediary performs cryptographic hash verification, maintains connection state tables, and filters packets before forwarding to the server. This intermediary role protects the original server from high interrupt rates during SYN flood attacks while preserving connection tracking accuracy.
3Reliability
If IP address whitelisting is implemented to allow only known good sources, then security against SYN flood attacks is improved, but synchronization issues and abuse potential arise from manual IP list management
Solution Approach 1:
The patent changes the authentication parameter from static IP address whitelisting to dynamic cryptographic hash verification. Instead of manually managing IP address lists, the system uses cryptographic functions that automatically verify connection legitimacy based on shared secrets. This parameter change eliminates synchronization issues and abuse potential associated with manual IP list management while maintaining strong security against SYN flood attacks.
Solution Approach 2:
The patent replaces the mechanical system of manual IP address list management with an automated cryptographic verification system. The protective proxy server uses cryptographic hash functions and shared secrets to automatically authenticate connections, eliminating the need for manual whitelisting and blacklisting operations. This substitution provides both security and ease of operation through automation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces CPU load and prevents SYN flood attacks by only forwarding fully established connections, while ensuring secure and legitimate TCP connections through authentication, thus enhancing network security and stability.
Implementation Method 1
A second value is computed using an authentication algorithm that includes at least using a cryptographic hash function that takes as input at least the source IP address of the encapsulating IP packet of the SYN segment and a shared secret between the TCP initiator and the TCP receiver.
Data Source
AI summary
A transparent TCP proxy device intercepts TCP connection requests received from a TCP client and destined for a TCP server as if acting as the TCP server in a handshake with the TCP client. Only after completing the handshake with the TCP client, the transparent TCP proxy participates in a handshake with the TCP server as if acting as the TCP client. After the handshake with the TCP server is complete, the transparent TCP proxy intercepts and translates subsequent TCP packets received from the TCP client and destined for the TCP server into a form expected by the TCP server including updating an acknowledgement number and TCP checksum; and intercepts and translates subsequent TCP packets received from the TCP server and destined for the TCP client into a form expected by the TCP client including updating an acknowledgement number and TCP checksum.