Document, method for authentication of a user, in particular for activation of a smart card function, and the computer system

The invention relates to a document with a non-volatile memory area for storing a secret identifier, wherein the identifier comprises a first n-character string from a predefined character set with random means for selecting at least one character from the predefined character set for replacing at least one character of the first string, so that a second n-character string is defined by this substitution, having a volatile storage area for storing the selected at least one character with a display device for displaying the selected at least one character, with input means for inputting a third string with processor means for authenticating to access the user to the document, wherein the processor means are adapted to the non-volatile memory area and the volatile storage area, so as to read the second character string and the second and third characters follow to check for compliance to authenticate the user.