SB n° 276: Clarification on UN CDA fail

EMV® Specification Bulletin No. 276 First Edition September 2022 _____________________________________________________ Clarification regarding UN in CDA signature verification This Specification Bulletin makes a clarification regarding the generation and use of Unpredictable Numbers during CDA signature verification _____________________________________________________

Applicability

This Specification Bulletin applies to

• EMV Integrated Circuit Card Specifications for Payment Systems, Book 2 – Security and Key Management, Version 4.3, November 2011.

Related Documents

• EMV Integrated Circuit Card Specifications for Payment Systems, Book 4 – Cardholder, Attendant and Acquirer Interface Requirements, Version 4.3, November 2011.
• Specification Bulletin No. 144, First Edition, June 2014 - Terminal Unpredictable Number Generation.

Effective Date

Immediate ____________________________________________________

Description

According to Book 4, as updated by Specification Bulletin No. 144, the terminal generates a 4-byte Unpredictable Number (UN, tag 9F37) to be used for input to the card cryptograms (Application Cryptograms and DDA/CDA signatures) to ensure the unpredictability of data input to this calculation and thereby the freshness of the cryptogram. A terminal may use the same UN value throughout a transaction, or it may generate a fresh UN every time one is requested by a card DOL, however the UN value used must always be unpredictable prior to the transaction. If an Unpredictable Number has not already been generated during the transaction then the terminal shall generate an Unpredictable Number before verifying the CDA signature. To make this clear a footnote is inserted into Book 2 section 6.6.2 that describes CDA signature verification. Proposed Change

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Add a footnote to Step 7 in section 6.6.2 of Book 2 as follows: 7. Concatenate from left to right the second to the sixth data elements in Table 22 (that is, Signed Data Format through Pad Pattern), followed by the Unpredictable Number.30A 30A If an Unpredictable Number has not already been generated for the current transaction, then the terminal shall generate an Unpredictable Number before performing this step.

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Legal Notice

The EMV® Specifications are provided “AS IS” without warranties of any kind, and EMVCo neither assumes nor accepts any liability for any errors or omissions contained in these Specifications. EMVCO DISCLAIMS ALL REPRESENTATIONS AND WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT, AS TO THESE SPECIFICATIONS. EMVCo makes no representations or warranties with respect to intellectual property rights of any third parties in or in relation to the Specifications. EMVCo undertakes no responsibility to determine whether any implementation of the EMV® Specifications may violate, infringe, or otherwise exercise the patent, copyright, trademark, trade secret, know-how, or other intellectual property rights of third parties, and thus any person who implements any part of the EMV® Specifications should consult an intellectual property attorney before any such implementation. Without limiting the foregoing, the Specifications may provide for the use of public key encryption and other technology, which may be the subject matter of patents in several countries. Any party seeking to implement these Specifications is solely responsible for determining whether its activities require a license to any such technology, including for patents on public key encryption technology. EMVCo shall not be liable under any theory for any party’s infringement of any intellectual property rights in connection with the EMV® Specifications

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