This Recommendation | International Standard will define those TTP services needed to support the application of digital signatures for the purpose of non-repudiation of creation of documents. This Recommendation | International Standard will also define interfaces and protocols to enable interoperability between entities associated with these TTP services. Definitions of technical services and protocols are required to allow for the implementation of TTP services and related commercial applications. This Recommendation | International Standard focuses on: – implementation and interoperability; – service specifications; and – technical requirements. This Recommendation | International Standard does not describe the management of TTPs or other organizational, operational or personal issues. Those topics are mainly covered in ITU-T Rec. X.842 | ISO/IEC TR 14516, Information technology – Security techniques – Guidelines on the use and management of Trusted Third Party services. NOTE 1 – Because interoperability is the main issue of this Recommendation | International Standard, the following restrictions hold: i) Only those services which may be offered by a TTP, either to end entities or to another TTP, are covered in this Recommendation | International Standard. ii) Only those services which may be requested and/or delivered by means of standardizable digital messages are covered. iii) Only those services for which widely acceptable standardized messages can be agreed upon at the time this Recommendation | International Standard is published are specified in detail. Further services will be specified in separate documents when widely acceptable standardized messages are available for them. In particular, time stamping services will be defined in a separate document. NOTE 2 – The data structures and messages in this Recommendation | International Standard will be specified in accordance to RFC documents, RFC 2510 and RFC 2511 (for certificate management services) and to RFC 2560 (for OCSP services). The certificate request format also allows interoperability with PKCS#10. See Annex C for references to the documents mentioned in this Note. NOTE 3 – Other standardization efforts for TTP services in specific environments and applications, like SET or EDIFACT, exist. These are outside of the scope of this Recommendation | International Standard. NOTE 4 – This Recommendation | International Standard defines technical specifications for services. These specifications are independent of policies, specific legal regulations, and organizational models (which, for example, might define how duties and responsibilities are shared between Certification Authorities and Registration Authorities). Of course, the policy of TTPs offering the services described in this Recommendation | International Standard will need to specify how legal regulations and the other aspects mentioned before will be fulfilled by the TTP. In particular, the policy has to specify how the validity of digital signatures and certificates is determined.