Recommendation ITU-T X.1156 provides a non-repudiation framework based on a one-time password (OTP) to enhance trust between transaction entities. In addition, this Recommendation describes the security requirements of OTP-based non-repudiation services, as well as the mechanisms for generating non-repudiation tokens. The originator of the transactions may request the trusted third party (TTP) to generate the non-repudiation token and the recipient may request the TTP to generate the non-repudiation of delivery token. Both the originator and the recipient may request TTP to verify the non-repudiation tokens.