A cryptographic pseudonym mapping method for an anonymous data sharing system, the method being adapted for generating a pseudonymised database from data relating to entities and originating from data sources (DS i), wherein the data are identified at the data sources (DS i) by entity identifiers of the respective entities, and wherein the data are identified in the pseudonymised database by pseudonyms, wherein the pseudonyms are assigned to the respective entity identifiers applying a one-to-one mapping, irrespective of the originating data source, by - applying one mapper and one key manager, - wherein the key manager is applied for - selecting a secret element (b) from a predetermined algebraic structure constituting a multiplicative or additive cyclic group, - selecting, for each data source (DS i) an element (e i, a i) to be applied as a cryptographic key by the given data source (DS i), from the algebraic structure and sending it to the given data source (DS i) while the element (e i, a i) is kept secret, - calculating an inverse (d i) of the element (e i, a i) in the given algebraic structure, and using it, together with the secret element (b), for generating a mapping cryptographic key (h i) of the mapper, the mapping cryptographic key (h i) corresponding to the given data source (DS i), and sending the mapping cryptographic key (h i) to the mapper while keeping it secret and assigned to the given data source (DS i), - transforming by the data source (DS i), each entity identifier to be mapped, into a respective encrypted entity identifier (C i) by using the element (e i, a i) to be applied as a cryptographic key, and - a respective pseudonym is generated by the mapper, for each encrypted entity identifier (C i) encrypted by the data source (DS i), utilizing the mapping cryptographic key (h i) corresponding to the particular data source (DS i). - applying one mapper and one key manager, - wherein the key manager is applied for - selecting a secret element (b) from a predetermined algebraic structure constituting a multiplicative or additive cyclic group, - selecting, for each data source (DS i) an element (e i, a i) to be applied as a cryptographic key by the given data source (DS i), from the algebraic structure and sending it to the given data source (DS i) while the element (e i, a i) is kept secret, - calculating an inverse (d i) of the element (e i, a i) in the given algebraic structure, and using it, together with the secret element (b), for generating a mapping cryptographic key (h i) of the mapper, the mapping cryptographic key (h i) corresponding to the given data source (DS i), and sending the mapping cryptographic key (h i) to the mapper while keeping it secret and assigned to the given data source (DS i), - selecting a secret element (b) from a predetermined algebraic structure constituting a multiplicative or additive cyclic group, - selecting, for each data source (DS i) an element (e i, a i) to be applied as a cryptographic key by the given data source (DS i), from the algebraic structure and sending it to the given data source (DS i) while the element (e i, a i) is kept secret, - calculating an inverse (d i) of the element (e i, a i) in the given algebraic structure, and using it, together with the secret element (b), for generating a mapping cryptographic key (h i) of the mapper, the mapping cryptographic key (h i) corresponding to the given data source (DS i), and sending the mapping cryptographic key (h i) to the mapper while keeping it secret and assigned to the given data source (DS i), - transforming by the data source (DS i), each entity identifier to be mapped, into a respective encrypted entity identifier (C i) by using the element (e i, a i) to be applied as a cryptographic key, and - a respective pseudonym is generated by the mapper, for each encrypted entity identifier (C i) encrypted by the data source (DS i), utilizing the mapping cryptographic key (h i) corresponding to the particular data source (DS i).