https://devzone.nordicsemi.com/f/nordic-q-a/10356/nrf51-ble-dfu-symmetric-signing-bootloader-dfu-upgradeI use the &quot; nrf51-ble-dfu-symmetric-signing &quot; example from GitHub. The application download over dfu works fine on the PCA10028 board. But how can I install this bootloader over dfu with the nRF Toolbox? The hmac_init_pkt_gen.py script createsen-USTelligent Community 13Fri, 20 Nov 2015 11:40:15 GMThttps://devzone.nordicsemi.com/thread/38432?ContentTypeID=1Fri, 20 Nov 2015 11:40:15 GMT137ad170-7792-4731-bb38-c0d22fbe4515:b74c047b-9858-4a83-aeb2-58a9c4b19a60Vidar Berg<p>Hi, the UICR section must be stripped from the .hex before you do the conversion to avoid the byte padding you mentioned. The bootloader won&#39;t and can&#39;t write to this area anyways; UICR registers can only be erased by doing a full chip erase (NVMC.ERASEALL).</p> <p>REMOTE DFU INVALID STATE could indicate the the device is not in DFU mode, did you try to enter DFU mode by pressing BOOTLOADER_BUTTON and doing a reset? LED 1 and 3 will be on when in DFU mode.</p> <p>Have you considered using the experimental assymteric signing example in the SDK (\nRF51_SDK_10.0.0\examples\dfu\experimental)? This example will be maintained by the SDK team.</p><div style="clear:both;"></div>