TLS Proxy Forward Secrecy via Ephemeral Value Hashing
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Solution Overview
Problem
The existing SSL/TLS protocol's reliance on insecure SSL termination points for decrypting pre-master secrets poses security risks, and the RSA proxy service, while offloading decryption, is vulnerable to replay attacks that compromise forward secrecy.
Innovation Solution
Implementing a cryptographic hash function to ensure that the ephemeral value used for server random value computation is never exposed in the clear, by offloading decryption to an external cryptographic server, which re-computes the server random value and maintains the secrecy of the pre-master secret.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SSL termination point decrypts the encrypted pre-master secret locally, then the decryption process is simple and direct, but the SSL termination point becomes insecure and the private key storage presents significant security risks
Solution Approach 1:
The patent extracts the private key storage and decryption functionality from the SSL termination point (edge server) and places it in a separate cryptographic server. The edge server sends the encrypted pre-master secret to the cryptographic server, which performs the decryption and returns the pre-master secret. This separation removes the security risk of storing private keys at the SSL termination point while maintaining the decryption functionality.
2Reliability
If the RSA proxy server decrypts the encrypted pre-master secret using a decryption key maintained at the server, then decryption is off-loaded from the SSL server, but the system becomes vulnerable to replay attacks that compromise forward secrecy
Solution Approach 1:
The patent implements preliminary action by having the edge server generate an ephemeral value and compute a server random value from it before sending the decryption request to the cryptographic server. The cryptographic server re-computes the server random value from the ephemeral value it receives. This preliminary computation ensures that even if the ephemeral value is transmitted in clear, it cannot be reused for replay attacks because the server random value is derived fresh each time, providing forward secrecy.
3Ease of operation
If the ephemeral value is transmitted in clear to the cryptographic server, then the server can re-compute the server random value, but the ephemeral value becomes exposed and potentially accessible to malicious third parties
Solution Approach 1:
The patent converts the potential harm of transmitting the ephemeral value in clear into a benefit by designing the system so that the ephemeral value is used to re-compute the server random value through a one-way function. Even though the ephemeral value is exposed during transmission, the cryptographic server uses it to regenerate the server random value, and the edge server immediately discards the original ephemeral value. This ensures forward secrecy because the exposed ephemeral value cannot be used to derive future secrets, and the one-way nature of the computation prevents reverse engineering.
Data Source
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AI summary
An infrastructure delivery platform provides a RSA proxy service as an enhancement to the TLS/SSL protocol to off-load, from an edge server to an external cryptographic server, the decryption of an encrypted pre-master secret. The technique provides forward secrecy in the event that the edge server is compromised, preferably through the use of a cryptographically strong hash function that is implemented separately at both the edge server and the cryptographic server. To provide the forward secrecy for this particular leg, the edge server selects an ephemeral value, and applies a cryptographic hash the value to compute a server random value, which is then transmitted back to the requesting client. That server random value is later re-generated at the cryptographic server to enable the cryptographic server to compute a master secret. The forward secrecy is enabled by ensuring that the ephemeral value does not travel on the wire.