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 Lawful Intercept

Lawful Interception of VoIP Traffic at an Internet Service Provider

Lawful Interception (LI) is the process by which traffic is intercepted for delivery to a law enforcement agency (LEA) based on a warrant or a court order. Most nations have some requirement for service providers to provide LI either already active or to be enacted in the near future. Because of the sensitive nature of LI, there are some requirements which need to be met.

  1. Access Control: Only authorized entities should be allowed to access intercepted information. Also, there may be restrictions on WHAT information is to be passed to the LEA (for example, only the caller information). Finally, undelivered information must be kept in such a way that if power is lost, that information is destroyed.

  2. Encryption Keys: Any encryption keys known by the service provider must also be passed to the LEA. To deal with the possibility of end-to-end encryption (i.e. using a key unknown to the service provider), The entire intercepted packet must be delivered.

  3. Secrecy: The interception must be done in such a way that the intercepted party is not aware of the interception taking place.

The architecture in Figure 1 is a reference model for implementing this type of LI.

LI reference model

Figure 1: Reference Model for this Type of LI Implemention

Using this architecture, the LEA sends a request to the LI system administrator. Based on the allowed level of access, either the intercept related information (IRI), content or both is then collected by the respective intercept access point (IAP) and delivered to the LEA.

Voice over IP (VoIP) traffic can be intercepted using this method. When the initial call information is placed, the system can detect this and record this information as the IRI. If the LEA is only authorized to receive the IRI, this information is passed to the LEA along with any other intercept related information. If the call information is to be collected, the IRI will contain the information needed to find and track that call such as the IP addresses and encoding scheme.

VOCAL has utilized its data and fax modem libraries for successful implementations of Lawful Interception.

To learn more about various applications of Lawful Interception, check out the following links: