SSL Session Key Extraction from Packet Traces
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Solution Overview
Problem
Existing methods for analyzing network traffic encrypted with SSL/TLS protocols require additional infrastructure, such as proxies, which incur overhead and alter traffic patterns, or rely on difficult-to-obtain private keys, making it challenging to decrypt and analyze encrypted data without disrupting communication.
Innovation Solution
A method that intercepts and uses session keys during handshaking between a client and server to decrypt packet-level traces without requiring private keys or proxies, utilizing a modified SSL library and TCP dump to capture and apply session keys for decryption, allowing for traffic analysis without additional infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SSL/TLS traffic is decrypted using existing methods, then traffic analysis can be performed, but additional infrastructure such as proxies is required which incurs overhead and alters traffic patterns
Solution Approach 1:
The patent extracts the session key from the SSL/TLS handshake process through packet capture and analysis, removing the need for proxy infrastructure. By capturing the handshake packets and deriving the session key from them, the system eliminates the middleman approach while maintaining decryption capability
Solution Approach 2:
The patent creates a copy of the session key during the handshake phase by analyzing captured packets. This copied key material is then used for decryption without requiring the original server private key or inserting proxy devices into the communication path
2Measurement precision
If SSL/TLS traffic is decrypted using private keys, then decryption can be achieved, but obtaining private keys of commercial servers is very difficult
Solution Approach 1:
The patent performs preliminary action by capturing the SSL/TLS handshake packets before the actual encrypted communication begins. During this preliminary phase, the session key is derived and stored, enabling subsequent decryption without needing to access the server's private key later
Solution Approach 2:
The patent uses captured handshake packets as an intermediary to derive the session key. Instead of directly accessing the server private key, the system uses the publicly exchanged handshake data as a mediator to obtain the decryption key material
3Measurement precision
If a man-in-the-middle SSL proxy is used to decrypt traffic, then SSL/TLS traffic can be decrypted, but additional overhead is incurred and traffic patterns are changed
Solution Approach 1:
The patent extracts the session key information from the captured handshake packets without requiring a proxy to be present in the communication path. This extraction approach eliminates the overhead associated with proxy devices while maintaining the ability to decrypt traffic
Solution Approach 2:
The system uses the already-existing handshake packets that are naturally exchanged during SSL/TLS connection establishment. By self-serving from these captured packets, the system avoids the overhead of additional proxy infrastructure that would otherwise be needed to intercept and decrypt traffic
Data Source
AI summary
An example first device disclosed herein is to obtain, from a library of the first device, a pre-master secret value and a master secret value associated with a session key for a communication session between the first device and a second device, the library instrumented to log the pre-master and master secret values during handshaking, the session key based on the pre-master secret value, the master secret value and data strings exchanged during the handshaking. The disclosed example first device is also to capture a packet level trace corresponding to the communication session, the packet level trace including the data strings and encrypted data. The disclosed example first device is further to determine the session key based on the pre-master secret value, the master secret value and the data strings without use of a proxy, and decrypt the encrypted data with the session key to obtain decrypted data.