Creating an IPEK from a given KSN and BDK

One time I asked one of our encryption experts:  "Can you describe to me how to create an Initial PIN Encryption Key ('IPEK') given a specific Base Derivation Key ('BDK') and Key Serial Number ('KSN')?  Since this was a test scenario, I wanted to know how to do it for some commonly used test values, namely:

BDK:    0123456789ABCDEF
KSN:    0123456789A00001

This was the very clear and descriptive answer provided to me:

I have a utility that creates a DUKPT PIN block, and I used that to come up with the IPEK of 78DF-942D-65A2-ECE6 (NOTE: dashes are provided here for clarity only). For DUKPT, the way the Initial PIN Encyption Key is derived is that the KSN is first padded to left with “F” to a length of 20 bytes (10 packed bytes). In the example provided, the Initial KSN ('IKSN') is FFFF0123456789A00001. Then, the right-most 21 bits of the packed IKSN are cleared (set to zero).

Then, the left-most 16 bytes (8 packed) of the IKSN are encrypted by the BDK; so, in this example FFFF0123456789A0 is encrypted with 0123456789ABCDEF as the key, resulting in a derived IPEK of 78DF-942D-65A2-ECE6.

Comments

[Ben Njouia Anis]

I think that the base derivation key (BDK) must be more longer ( 128 bits)...

[tim]

How do you get a iskn and bdk;if not given.

[FIkri]

Yes, I think Ben was right, according to Thales BDK generation tools, it produces a 32 digits of BDK value. I wanted to know what kind of utility that you have to creates a DUKPT PIN-Block ?

[Andy Orrock]

This Wikipedia post explains the relationship between the BDK and IPEK:

http://www.andyorrock.com/2006/09/creating_an_ipe.html

[Matt]

Ben/Flkri - you're both wrong. He has a 16 byte BDK which is 128 bits (16*8 = 128)...

[Hien]

Hi Andy

Could you please explain more on "IKSN are encrypted by the BDK", what method is using to encrypt IKSN here? I though XOR but seem not true

Thanks