An anonymous linking code is an encrypted key for linking data from dierent sources. So far, quite simple algorithms for the generation of such codes based on personal characteristics as names and date of birth are in common use. These algorithms will yield many non matching codes when facing errors in the underlying indentifier values. We suggested the use of Bloom filters for calculating string similarities in a privacy-preserving manner. Here, we claim that this principle can also be used for a novel error-tolerant but still irreversible encrypted key. We call the proposed code Cryptographic Longterm Key. It consists of one single Bloom filter into which identfiers are subsequently stored. Tests on simulated databases yield linkage results comparable to non encrypted identifiers and superior to results from hitherto existing methods. Since the Cryptographic Longterm Key can be easily adapted to meet quite dierent prerequisites it might be useful for many applications.