Abstract: A system and method for request verification in an Application Level Gateway (ALG) located between a client and a server in a data transmission network. The ALG receives from a server a message that requires some responsive actions from a client. The ALG adds to this message Verification Data (VD) that includes information about expected actions required from the client. The ALG then sends the message with the above-mentioned additions to the client. The client receives this message and sends a response, with the actual actions and with the VD, to the server. The ALG obtains this response with the VD, and compares the description of the expected actions with actual actions of the client. If the actions of the client are legitimate, the ALG sends the client response to the server.

Abstract: An Application Level Gateway (ALG) based on an universal parser, in a data transmission network. This ALG enables all data flow of an application level protocol to be checked for concordance with the formal syntax description of the data transmission protocol, and with a security policy. The ALG contains a transmission controller, universal parser, and at least one parser plug-in for each universal parser. This parser plug-in is specific to the data transmission protocol, and can be automatically created from the formal syntax description of a data transmission protocol. A security policy (rules, restrictions) can be implemented in the parser plug-in and/or in the settings.

Abstract: A system and method for request verification in an Application Level Gateway (ALG) located between a client and a server in a data transmission network. The ALG receives from a server a message that requires some responsive actions from a client. The ALG adds to this message Verification Data (VD) that includes information about expected actions required from the client. The ALG then sends the message with the above-mentioned additions to the client. The client receives this message and sends a response, with the actual actions and with the VD, to the server. The ALG obtains this response with the VD, and compares the description of the expected actions with actual actions of the client. If the actions of the client are legitimate, the ALG sends the client response to the server.