A cryptographic pseudonym mapping method for an anonymous data sharing system, the method being adapted for generating a pseudonymised database (DB) 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 (D) of the respective entities, and wherein the data are identified in the pseudonymised database (DB) by pseudonyms (P), wherein the pseudonyms (P) are assigned to the respective entity identifiers (D) applying a one-to-one mapping, irrespective of the originating data source, by - applying more than one, a number k of mappers (M j ), - selecting for each data source (DS i ) elements (d ij, a ij ) in a number equal to the number of mappers (M j ) from a predetermined algebraic structure constituting a multiplicative or an additive cyclic group, of which elements (d ij, a ij ) one element (d ij, a ij ) is sent, while being kept secret and kept assigned to the data source (DS i ), to each mapper (M j ), calculating from the plurality of elements (d ij, a ij ) an inverse cryptographic key of said plurality, and transforming, each entity identifier (D) to be mapped, into a respective encrypted entity identifier (C i0 ) by using the inverse cryptographic key as an own secret cryptographic key (e i ) of the data source (DS i ), - generating for each mapper (M j ) its mapping cryptographic key (h ij ) corresponding to the data source (DS i ) by using the element (d ij, a ij ) that was sent to the mapper (M j ) and an element (b j ) selected randomly from the algebraic structure and kept secret by the mapper (M j ), and - generating respective pseudonyms (P) by sequentially performing, in a permutation of the mappers (M j ), a number k of mappings utilizing the mapping cryptographic keys (h ij ) of the mappers (M j ) belonging to the particular data source (DS i ) on each encrypted entity identifier (C i0 ) encrypted by the data source (DS i ). - applying more than one, a number k of mappers (M j ), - selecting for each data source (DS i ) elements (d ij, a ij ) in a number equal to the number of mappers (M j ) from a predetermined algebraic structure constituting a multiplicative or an additive cyclic group, of which elements (d ij, a ij ) one element (d ij, a ij ) is sent, while being kept secret and kept assigned to the data source (DS i ), to each mapper (M j ), calculating from the plurality of elements (d ij, a ij ) an inverse cryptographic key of said plurality, and transforming, each entity identifier (D) to be mapped, into a respective encrypted entity identifier (C i0 ) by using the inverse cryptographic key as an own secret cryptographic key (e i ) of the data source (DS i ), - generating for each mapper (M j ) its mapping cryptographic key (h ij ) corresponding to the data source (DS i ) by using the element (d ij, a ij ) that was sent to the mapper (M j ) and an element (b j ) selected randomly from the algebraic structure and kept secret by the mapper (M j ), and - generating respective pseudonyms (P) by sequentially performing, in a permutation of the mappers (M j ), a number k of mappings utilizing the mapping cryptographic keys (h ij ) of the mappers (M j ) belonging to the particular data source (DS i ) on each encrypted entity identifier (C i0 ) encrypted by the data source (DS i ). <EOS>