https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1744347#M10892 <P>Hi <a href="https://community.nxp.com/t5/user/viewprofilepage/user-id/217291">@echai</a> ,</P><P><SPAN>Now I’m stuck at this step, and I’m also using JavaScript. Have you passed this step</SPAN>?</P><P><SPAN class=""><SPAN>Any help appreciated.</SPAN></SPAN></P> Mon, 23 Oct 2023 08:51:30 GMT zahra2023 2023-10-23T08:51:30Z https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1650370#M10339 <P>Hi everyone, I am currently trying to write the ChangeKey command implementation in Javascript. I ran into a few blockers &amp; questions, and would like some clarification &amp; help. I've read through both the Product Data Sheet &amp; Application Note, and here is where I am stuck at:<BR /><BR /></P><P>1. How is Step 15 derived? My assumption (based on purely looking at related values) is that the Input for CMAC is made up of: <EM>Change Key Command (INS) || CmdCtr || TI || Value from Step 12</EM><BR />Is this assumption correct? Where did C4 come from?<BR /><BR />2. Even using values from Table 26, I cannot get the value for Step 17. I attempted to generate a CMAC using the&nbsp;<EM>IV for CMACing</EM> as the CMAC key and the <EM>Input for CMAC</EM> as the value itself. This is most definitely wrong, as I cannot get the correct values. What values do I CMAC together to get the value in Step 17, and how is the IV for CMACing used?<BR /><BR />Thank you!</P><P><span class="lia-inline-image-display-wrapper lia-image-align-center" image-alt="Screenshot 2023-05-15 at 9.48.35 PM.png" style="width: 587px;"><img src="https://community.nxp.com/t5/image/serverpage/image-id/223619i75FA3FB0D821B6C0/image-size/large?v=v2&amp;px=999" role="button" title="Screenshot 2023-05-15 at 9.48.35 PM.png" alt="Screenshot 2023-05-15 at 9.48.35 PM.png" /></span></P><P>&nbsp;</P> Wed, 17 May 2023 13:53:02 GMT https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1650370#M10339 echai 2023-05-17T13:53:02Z https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1655247#M10369 <P>Hi&nbsp;</P> <P>C4H is ChangeKey command's command code.</P> <P>&nbsp;</P> <P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="danielchen_0-1684818387182.png" style="width: 718px;"><img src="https://community.nxp.com/t5/image/serverpage/image-id/224341iCD0A2388B96CC962/image-dimensions/718x544?v=v2" width="718" height="544" role="button" title="danielchen_0-1684818387182.png" alt="danielchen_0-1684818387182.png" /></span></P> <P>&nbsp;</P> <P>Regards</P> <P>Daniel</P> <P>&nbsp;</P> <P>&nbsp;</P> Tue, 23 May 2023 05:07:03 GMT https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1655247#M10369 danielchen 2023-05-23T05:07:03Z https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1744347#M10892 <P>Hi <a href="https://community.nxp.com/t5/user/viewprofilepage/user-id/217291">@echai</a> ,</P><P><SPAN>Now I’m stuck at this step, and I’m also using JavaScript. Have you passed this step</SPAN>?</P><P><SPAN class=""><SPAN>Any help appreciated.</SPAN></SPAN></P> Mon, 23 Oct 2023 08:51:30 GMT https://community.nxp.com/t5/NFC/How-to-calculate-the-CMAC-value-used-in-ChangeKey-command-for/m-p/1744347#M10892 zahra2023 2023-10-23T08:51:30Z