A method and system for authentication of a user (302, 402) by an authenticating entity (304, 404). The method including the authenticating entity (304, 404) sending a challenge (310, 410) to the user (302, 402). The user (302, 402) adds a spoiler to the challenge (312, 412) and encrypts (316, 416) the combined spoiler and challenge (314, 414) using a private key of an asymmetric key pair. The user (302, 402) sends the encrypted combined spoiler and challenge to the authenticating entity (304, 404). The authenticating entity (304, 404) ascertains that the returned challenge is the same the original challenge (310, 410) and approves the user (302, 402).