Methods, apparatuses, and computer program products for providing fresh security context during intersystem mobility

An apparatus comprising:

• at least one processor;
• and
• at least one memory, wherein the at least one processor and the at least one memory are configured to at least:
• receive, at the apparatus, an indication of handover of a remote device from a source system to a target system, wherein the target system implements a communications standard different from the source system;
• determine, at the apparatus, a sequence value of a security context maintained in the source system;
• derive, at the apparatus, another security context for the target system based at least in part on the determined sequence value;
• and
• provide, by the apparatus, the other security context to the target system,
• wherein the source system implements an evolved universal terrestrial radio access network communications standard, wherein the determine comprises determining a non-access stratum downlink count, and wherein the derive comprises calculating a cipher key and an integrity key based at least in part upon the determined non-access stratum downlink count.

A method comprising:

• receiving, at a network element, an indication of handover of a remote device from a source system to a target system, wherein the target system implements a communications standard different from the source system;
• determining, at the network element, a sequence value of a security context maintained in the source system;
• deriving, at the network element, another security context for the target system based at least in part on the determined sequence value;
• and
• providing, by the network element, the other security context to the target system,
• wherein the source system implements an evolved universal terrestrial radio access network communications standard, wherein the determining comprises determining a non-access stratum downlink count, and wherein the deriving comprises calculating a cipher key and an integrity key based at least in part upon the determined non-access stratum downlink count.