Sec-ALG: An Open-source Application Layer Gateway for Secure Access to Private Networks

Middleboxes such as Network Address Translators (NATs), proxy servers or Application Layer Gateways (ALGs) provide remote access to end-hosts in the private address space. The middleboxes offer proprietary solutions and encrypted traffic poses a challenge when middleboxes employ packet payload inspection techniques for connection establishment. Session key sharing and decryption followed by re-encryption of the traffic, for correctly routing to the private host, increases the connection latency and also poses a higher threat in case of traffic interception by a malicious third-party. In this paper, we present a novel open-source ALG, called Sec-ALG, for providing secure end-to-end communication to the web servers situated in the private address space. Sec-ALG relies on the technique of light Deep Packet Inspection (DPI) for protocol detection and session establishment using a novel parser-lexer generator called YaLe. The proposed approach offers increased security by maintaining end-to-end encryption for an HTTPS connection. Our experimental analysis demonstrates that Sec-ALG reduces the HTTPS connection latency in comparison to the NGINX reverse proxy using a 24-core host machine. Moreover, Sec-ALG handles requests at a three-fold increased rate than NGINX proxy when tested with 100 concurrent connections. The ALG can be used either as a standalone solution or a component of the Realm Gateway, that is a generic interworking solution between public and private networks. The presented work is part of an extensive ongoing research at Aalto University focusing on embedding policy based trust into the network.