signer IEEE address (8-byte), signature data (72-byte)
ECDSA certificate (48-byte)
ECDSA certificate (74-byte)
hash value (16-byte)
2-byte header before actual UpgradeImage
see https://github.com/telink-semi/telink_zigbee_sdk/blob/d5bc2f7b0c1f8536fe21c8127ca680ea8214bc8e/tl_zigbee_sdk/zigbee/ota/ota.h#L38
signer IEEE address (8-byte), signature data (42-byte)