This report constitutes a requirements specification for a cryptographic algorithm which is used to protect General Packet Radio Services (GPRS) as specified by GSM 02.60. This specification is intended to provide the ETSI Security Algorithms Group of Experts (SAGE) with the information it requires in order to design and deliver a technical specification for such an algorithm. The specification covers the intended use of the algorithm and use of the algorithm specification, technical requirements on the algorithm, requirements on the algorithm specification and test data, and quality assurance requirements on both the algorithm and its documentation. The specification also outlines the background to the production of this specification.