Non-repudiation is to prevent entities from denying that they have sent or received electronic transaction data in the telecommunication network. Recommendation ITU-T X.1159 provides delegated non-repudiation architecture to generate non-repudiation evidence by a trusted third party instead of a user. Recommendation ITU-T X.813 defines six non-repudiation mechanisms: a trusted third party (TTP) security token, security tokens and tamper-resistant modules, a digital signature, time stamping and an in-line TTP and notary. This Recommendation complies with the six mechanisms, and the non-repudiation service can use a combination of these mechanisms to satisfy the security requirements of the application service. In this Recommendation, a right and/or user's signing key for a non-repudiation generation delegates to TTP, which is a central signing authority, and the central signing authority generates and verifies non-repudiation evidence using the delegated user's signing/validation key or the central signing authority's secret key/validation key. The delegated non-repudiation model in this Recommendation is capable to respond to key loss and theft, it is safe in an open network, such as a mobile and cloud network, and it provides convenient non-repudiation service. This Recommendation describes the delegated non-repudiation service models and operations for each of the service models. The architecture also defines the security requirements of the delegated non-repudiation service. In this delegated non-repudiation service model, there are two types of service models that use the central signing authority's secret key and the delegated signing key.