What Needs to Be Signed

A digital signature is useful for linking different data together, but not all of the information in a PIDF-LO needs to be protected by the digital signature. If a PIDF-LO is generated by an LIS, certain information must be signed for the signature to be effective, but other elements can be unsigned so that it can be changed.

The following pieces of information must be signed for a digital signature to have any effect:

• Location information The location information is the primary piece of interesting data.

• The presentity identifier This field identifies the subject of location information; a link between location and identity is the most important factor in protecting against theft of location information.

• Time limits A timestamp indicates the time that the location information was generated, and an expiry time ensures that the information cannot be used beyond the time when it is deemed valid.

All of this information is already present in the PIDF-LO document, except that an explicit expiry time is not provided for. A new element, the domain-auth element, is added to provide this information, and to house the digital signature elements. The name is derived from the fact that the information is authorized by the operator of the access network, or network domain.