The firmware included a BLAKE2s digest of the expected device app in the first app slot. The firmware refuses to start the app if the computed digest differs from the constant.

To simplify computing the digest, use this tool with the -c flag for including the digest in a C program:

Building

go build

Running

./b2s -m b2s -c
// BLAKE2s digest of b2s
uint8_t digest[32] = {
0x17, 0x36, 0xe9, 0x4e, 0xeb, 0x1b, 0xa2, 0x30, 0x89, 0xa9, 0xaa, 0xe, 0xf2, 0x6f, 0x35, 0xb2, 0xa9, 0x89, 0xac, 0x64, 0x63, 0xde, 0x38, 0x60, 0x47, 0x40, 0x91, 0x4e, 0xd7, 0x72, 0xa0, 0x58,
};

To print the digest in a more user friendly way, leave out the -c:

./b2s -m b2s
1736e94eeb1ba23089a9aa0ef26f35b2a989ac6463de38604740914ed772a058 b2s