In practical applications, one would have several BDKs on record, possibly for different customers, or to contain the scope of key compromise. When processing transactions, it is important for the receiver to know which BDK was used to initialize the originating device. To achieve this, the 80-bit KSN is structured into three parts: as Key Set ID, a TRSM ID, and the transaction counter. The algorithm specifies that the transaction counter is 21-bits, but treats the remaining 59 bits opaquely (the algorithm only specifies that unused bits be 0-padded to a nibble boundary, and then 'f' padded to the 80-bit boundary). Because of this, the entity managing the creation of the DUKPT devices (typically a merchant acquirer) is free to subdivide the 59 bits according to their preference.