SB nº AN-19 : Clarification of Odd parity requirements during session key derivation (Clarification)

Application Note N° 19 First Edition: February 24th, 2004 Clarification of Odd Parity Requirements during Session Key Derivation This Application Note clarifies EMV 2000 Integrated Circuit Card Specifications for Payment Systems Version 4.0 Book 2 Security and Key Management Section A1.3 Session Key Derivation regarding the use of odd parity and DES keys. Since the DES algorithm does not actually require that DES keys have odd parity (the least significant bit of each key byte is not used) the least significant bits do not affect the output. However, when a value (such as an intermediate key) is used as data input to the DES algorithm then the least significant bits are used and do affect the output. In EMV 2000 Integrated Circuit Card Specifications for Payment Systems Version 4.0 Book 2 Security and Key Management, please replace the last paragraph in Section A1.3.1 that starts with "The session key SK is defined to be X…" with the following paragraph: The session key SK is defined to be X. Optionally the least significant bit of each byte of the session key may be set to provide odd parity. Note that parity forcing shall not take place for the intermediate keys when used as data input to the next step. In Section A1.3.2 of the same book, please change the last line of the code after the third paragraph to the following: SK=PAR(Φ(P,GP,aH-1)⊕GP); (Note: parity forcing is optional.) Please change the next to last line of the code before the final paragraph in the same section to the following: SK=PAR(Φ(P,GP,aH-1)⊕GP); (Note: parity forcing is optional.) 1