diff --git a/embed/boardloader/main.c b/embed/boardloader/main.c
index a98562e63..4d0543682 100644
--- a/embed/boardloader/main.c
+++ b/embed/boardloader/main.c
@@ -60,7 +60,7 @@ bool copy_sdcard(void)
     display_printf("erasing flash ");
 
     // erase flash (except boardloader)
-    if (0 != flash_erase_sectors(FLASH_SECTOR_BOARDLOADER_END + 1, FLASH_SECTOR_FIRMWARE_END, progress_callback)) {
+    if (!flash_erase_sectors(FLASH_SECTOR_BOARDLOADER_END + 1, FLASH_SECTOR_FIRMWARE_END, progress_callback)) {
         display_printf(" failed\n");
         return false;
     }
@@ -81,21 +81,25 @@ bool copy_sdcard(void)
         return false;
     }
 
-    HAL_FLASH_Unlock();
+    if (!flash_unlock()) {
+        display_printf("could not unlock flash\n");
+        return false;
+    }
+
     for (int i = 0; i < (HEADER_SIZE + hdr.codelen) / SDCARD_BLOCK_SIZE; i++) {
         sdcard_read_blocks((uint8_t *)buf, i, 1);
         for (int j = 0; j < SDCARD_BLOCK_SIZE / sizeof(uint32_t); j++) {
             if (HAL_FLASH_Program(FLASH_TYPEPROGRAM_WORD, BOOTLOADER_START + i * SDCARD_BLOCK_SIZE + j * sizeof(uint32_t), buf[j]) != HAL_OK) {
                 display_printf("copy failed\n");
                 sdcard_power_off();
-                HAL_FLASH_Lock();
+                flash_lock();
                 return false;
             }
         }
     }
 
     sdcard_power_off();
-    HAL_FLASH_Lock();
+    flash_lock();
 
     display_printf("done\n");
 
diff --git a/embed/bootloader/messages.c b/embed/bootloader/messages.c
index a456da7b1..0f4931905 100644
--- a/embed/bootloader/messages.c
+++ b/embed/bootloader/messages.c
@@ -240,7 +240,13 @@ void process_msg_FirmwareErase(uint8_t iface_num, uint32_t msg_size, uint8_t *bu
     firmware_remaining = msg_recv.has_length ? msg_recv.length : 0;
     if (firmware_remaining > 0 && firmware_remaining % 4 == 0) {
         // erase flash
-        flash_erase_sectors(FLASH_SECTOR_FIRMWARE_START, FLASH_SECTOR_FIRMWARE_END, progress_erase);
+        if (!flash_erase_sectors(FLASH_SECTOR_FIRMWARE_START, FLASH_SECTOR_FIRMWARE_END, progress_erase)) {
+            MSG_SEND_INIT(Failure);
+            MSG_SEND_ASSIGN_VALUE(code, FailureType_Failure_ProcessError);
+            MSG_SEND_ASSIGN_STRING(message, "Could not erase flash");
+            MSG_SEND(Failure);
+            return;
+        }
         // request new firmware
         chunk_requested = (firmware_remaining > FIRMWARE_CHUNK_SIZE) ? FIRMWARE_CHUNK_SIZE : firmware_remaining;
         MSG_SEND_INIT(FirmwareRequest);
@@ -284,11 +290,18 @@ static bool _read_payload(pb_istream_t *stream, const pb_field_t *field, void **
 
 void process_msg_FirmwareUpload(uint8_t iface_num, uint32_t msg_size, uint8_t *buf)
 {
-    HAL_FLASH_Unlock();
+    if (!flash_unlock()) {
+        MSG_SEND_INIT(Failure);
+        MSG_SEND_ASSIGN_VALUE(code, FailureType_Failure_ProcessError);
+        MSG_SEND_ASSIGN_STRING(message, "Could not unlock flash");
+        MSG_SEND(Failure);
+        return;
+    }
+
     MSG_RECV_INIT(FirmwareUpload);
     MSG_RECV_CALLBACK(payload, _read_payload);
     MSG_RECV(FirmwareUpload);
-    HAL_FLASH_Lock();
+    flash_lock();
 
     if (chunk_size != chunk_requested) {
         MSG_SEND_INIT(Failure);
diff --git a/embed/trezorhal/flash.c b/embed/trezorhal/flash.c
index 2288d9eff..833760176 100644
--- a/embed/trezorhal/flash.c
+++ b/embed/trezorhal/flash.c
@@ -1,5 +1,8 @@
 #include STM32_HAL_H
 
+#include <string.h>
+#include "flash.h"
+
 int flash_init(void)
 {
     return 0;
@@ -39,12 +42,26 @@ void flash_set_option_bytes(void)
     }
 }
 
-int flash_erase_sectors(int start, int end, void (*progress)(uint16_t val))
+bool flash_unlock(void)
 {
     HAL_FLASH_Unlock();
-    FLASH_EraseInitTypeDef EraseInitStruct;
     __HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_EOP | FLASH_FLAG_OPERR | FLASH_FLAG_WRPERR |
                            FLASH_FLAG_PGAERR | FLASH_FLAG_PGPERR | FLASH_FLAG_PGSERR);
+    return true;
+}
+
+bool flash_lock(void)
+{
+    HAL_FLASH_Lock();
+    return true;
+}
+
+bool flash_erase_sectors(int start, int end, void (*progress)(uint16_t val))
+{
+    if (!flash_unlock()) {
+        return false;
+    }
+    FLASH_EraseInitTypeDef EraseInitStruct;
     EraseInitStruct.TypeErase = FLASH_TYPEERASE_SECTORS;
     EraseInitStruct.VoltageRange = FLASH_VOLTAGE_RANGE_3;
     EraseInitStruct.NbSectors = 1;
@@ -52,13 +69,65 @@ int flash_erase_sectors(int start, int end, void (*progress)(uint16_t val))
     for (int i = start; i <= end; i++) {
         EraseInitStruct.Sector = i;
         if (HAL_FLASHEx_Erase(&EraseInitStruct, &SectorError) != HAL_OK) {
-            HAL_FLASH_Lock();
-            return 0;
+            flash_lock();
+            return false;
         }
         if (progress) {
             progress(1000 * (i - start + 1) / (end - start + 1));
         }
     }
-    HAL_FLASH_Lock();
-    return 1;
+    flash_lock();
+    return true;
+}
+
+#define FLASH_OTP_LOCK_BASE       0x1FFF7A00U
+#define FLASH_OTP_NUM_BLOCKS      16
+#define FLASH_OTP_BLOCK_SIZE      32
+
+bool flash_otp_write(uint8_t block, uint8_t offset, const uint8_t *data, uint8_t datalen)
+{
+    if (block >= FLASH_OTP_NUM_BLOCKS || offset + datalen > FLASH_OTP_BLOCK_SIZE) {
+        return false;
+    }
+    if (!flash_unlock()) {
+        return false;
+    }
+    HAL_StatusTypeDef ret;
+    for (uint8_t i = 0; i < datalen; i++) {
+        ret = HAL_FLASH_Program(FLASH_TYPEPROGRAM_BYTE, FLASH_OTP_BASE + block * FLASH_OTP_BLOCK_SIZE + offset + i, data[i]);
+        if (ret != HAL_OK) {
+            break;
+        }
+    }
+    flash_lock();
+    return ret == HAL_OK;
+}
+
+bool flash_otp_read(uint8_t block, uint8_t offset, uint8_t *data, uint8_t datalen)
+{
+    if (block >= FLASH_OTP_NUM_BLOCKS || offset + datalen > FLASH_OTP_BLOCK_SIZE) {
+        return false;
+    }
+    for (uint8_t i = 0; i < datalen; i++) {
+        data[i] = *(__IO uint8_t *)(FLASH_OTP_BASE + block * FLASH_OTP_BLOCK_SIZE + offset + i);
+    }
+    return true;
+}
+
+bool flash_otp_lock(uint8_t block)
+{
+    if (block >= FLASH_OTP_NUM_BLOCKS) {
+        return false;
+    }
+    if (!flash_unlock()) {
+        return false;
+    }
+    HAL_StatusTypeDef ret = HAL_FLASH_Program(FLASH_TYPEPROGRAM_BYTE, FLASH_OTP_LOCK_BASE + block, 0x00);
+    flash_lock();
+    return ret == HAL_OK;
+}
+
+bool flash_otp_is_locked(uint8_t block)
+{
+    return *(__IO uint8_t *)(FLASH_OTP_LOCK_BASE + block) == 0x00;
 }
diff --git a/embed/trezorhal/flash.h b/embed/trezorhal/flash.h
index 00d52863b..0816832af 100644
--- a/embed/trezorhal/flash.h
+++ b/embed/trezorhal/flash.h
@@ -1,12 +1,9 @@
 #ifndef __TREZORHAL_FLASH_H__
 #define __TREZORHAL_FLASH_H__
 
+#include <stdbool.h>
 #include <stdint.h>
 
-int flash_init(void);
-
-void flash_set_option_bytes(void);
-
 #define FLASH_SECTOR_BOARDLOADER_START 0
 #define FLASH_SECTOR_BOARDLOADER_END   1
 
@@ -19,6 +16,18 @@ void flash_set_option_bytes(void);
 #define FLASH_SECTOR_FIRMWARE_START    5
 #define FLASH_SECTOR_FIRMWARE_END      11
 
-int flash_erase_sectors(int start, int end, void (*progress)(uint16_t val));
+int flash_init(void);
+
+void flash_set_option_bytes(void);
+
+bool flash_unlock(void);
+bool flash_lock(void);
+
+bool flash_erase_sectors(int start, int end, void (*progress)(uint16_t val));
+
+bool flash_otp_write(uint8_t block, uint8_t offset, const uint8_t *data, uint8_t datalen);
+bool flash_otp_read(uint8_t block, uint8_t offset, uint8_t *data, uint8_t datalen);
+bool flash_otp_lock(uint8_t block);
+bool flash_otp_is_locked(uint8_t block);
 
 #endif