General • Re: How do you hide a RP2350 OTP secret from picotool?

Code:

// Lock page 32#include <stdio.h>#include "pico/stdlib.h"#include "pico/bootrom.h"#include "hardware/structs/otp.h"int main(){  stdio_init_all();  // Values to write to the lock registers  uint32_t LockMask = 0x3d3d3d;   otp_cmd_t Cmd;  for (int i=0; i<5; i++)  {    printf("Sleep %d\n", i);    sleep_ms(1000);  }  printf("Locking page 32\n");        // Lock Page 32 (Row 0x0fc1)  Cmd.flags = (0x0fc1 & 0xffff) | 0x00010000; // ROW_NUMBER | IS_WRITE  int ret = rom_func_otp_access((uint8_t*)&LockMask, 4, Cmd);  printf("Page 32 lock result=%d\n", ret);  }

Code:

$ sudo picotool otp get --raw OTP_DATA_PAGE32_LOCK1ROW 0x0fc1: OTP_DATA_PAGE32_LOCK1        "Lock configuration MSBs for page 32 (rows 0x800 through 0x83f). Locks are stored        with 3-way majority vote encoding, so that bits can be set independently. This OTP        location is always readable, and is write-protected by its own permissions."    VALUE 0x3d3d3d

Code:

$ sudo picotool otp get --raw 0x0800ERROR: The RP2350 device returned an error: permission failure

Code:

int get_private_key(uint8_t* buffer_out){  otp_cmd_t cmmd;    // Target User Row 0x800 and set IS_ECC bit for hardware error correction  cmd.flags = (0x800 & OTP_CMD_ROW_BITS) | OTP_CMD_ECC_BITS;  // In ECC mode, 32 bytes of data are retrieved from 16 rows (2 bytes per row)  int ret= rom_func_otp_access(buffer_out, 32, cmd);  printf("rom_func_otp_access ret=%d!\n", ret);  return ret;}