A hash value provides for a time-stamp for a piece of data upon verification. Providing the hash value includes deriving one-time signing keys of signer's one-time signing key hash chain by a one-way function of a secret key of the signer and a function of an index of the one-time signing key, and providing the hash value for the piece of data by a hash function including the piece of data and the derived one-time signing key. An electronic device having a processor arranged to implement a functional module for deriving a one-time signing key and providing a hash value for a piece of data by a hash function including the piece of data and the derived one-time signing key is also disclosed. The functional module is arranged to perform the method. A computer program for implementing the method on the electronic device is also disclosed.