# iodd ST400 / MINI PRO Duress PIN Guide - Plausible Deniability Mode with `vhd4.vhd` This guide explains how to use the **Duress PIN - For Plausible Deniability Mode** feature on iodd **ST400** and **MINI PRO** devices. With firmware version 82 or later, a device updated using `iodd_firm_upd-0.8.2.0_xx.exe` or later can show only the `vhd4.vhd` virtual disk on the PC in Plausible Deniability Mode. In this mode, the PC does not see the normal physical partition. It sees only the fixed-size VHD file prepared as `vhd4.vhd`, allowing the device to present a separate, shareable volume while keeping the normal storage area separate. **Supported products:** iodd **ST400** and **MINI PRO** updated to **firmware version 82 or later** using `iodd_firm_upd-0.8.2.0_xx.exe` or later. --- ## 1. How to Create and Use `vhd4.vhd` The basic procedure is as follows. 1. Unlock the device with a PIN other than the **User 4 PIN**. 2. On the PC, create the `vhd4.vhd` file in the **root folder** of the first partition. 3. Make sure `vhd4.vhd` is in the root folder, not in a subfolder. 4. Return to the root folder list on the device screen. 5. Press **Key 1** to rebuild the root folder list. You can also reboot the device, or enter a subfolder and return to the root folder. 6. When `vhd4.vhd` appears in the list, the device updates the VHD setting. 7. Unlock the device again with the **User 4 PIN**. 8. The PC shows a disk whose size matches `vhd4.vhd`. Important points: - The file name must be exactly `vhd4.vhd`. - The file must be located in the root folder of the first partition. - `vhd4.vhd` must be stored contiguously on the disk. It must be a **fixed-size VHD** file, not a dynamic VHD and not a VHDX file. - After creating `vhd4.vhd`, the root folder list must be rebuilt. Use **Key 1**, reboot the device, or enter a subfolder and return to the root folder. - Rebuild the root folder list only while unlocked with a PIN other than the User 4 PIN. - However, a user with **disk write protection** cannot update the VHD setting. --- ## 2. Normal PIN vs Duress PIN | Type | Purpose | What the PC Sees | | ----------------------- | -------------------------------------------------------------- | ------------------------- | | PIN other than User 4 | File management, ISO/VHD management, `vhd4.vhd` setting update | Normal physical partition | | User 4 PIN (Duress PIN) | `vhd4.vhd` use | Disk sized to `vhd4.vhd` | When you unlock with a PIN other than the User 4 PIN, you can see the files in the root folder. In this state, create or delete `vhd4.vhd`, then rebuild the root folder list to update the setting. The User 4 PIN works as the Duress PIN and shows only `vhd4.vhd` in Plausible Deniability Mode. When you unlock with the User 4 PIN, the device does not scan the root folder again. Before using the User 4 PIN, update the `vhd4.vhd` setting first while unlocked with a PIN other than the User 4 PIN. A user with disk write protection cannot update the `vhd4.vhd` setting. --- ## 3. `vhd4.vhd` File Requirements `vhd4.vhd` must meet the following requirements. | Item | Requirement | | --------- | ---------------------------------- | | File name | `vhd4.vhd` | | Location | Root folder of the first partition | | Format | Fixed-size VHD file, not dynamic VHD or VHDX | | Placement | Contiguous, without fragmentation | Select `vhd4.vhd` and press **Key 5** to display the file information message. The `fragment` value in this message must be `1`. A fragmented `vhd4.vhd` cannot be used. If the LCD shows a defragmentation or `DEFRAG` message, recreate `vhd4.vhd` as a contiguous file on the PC, then unlock with a PIN other than the User 4 PIN and rebuild the root folder list. --- ## 4. Rebuilding the Root Folder List The device checks whether `vhd4.vhd` exists when it builds the root folder list. When creating `vhd4.vhd`, use **VHD_Tool++ v0.9.0.10 or later** from the iODD VHD tools page: . This is a **Windows-only** tool. If you cannot use VHD_Tool++, format the drive and create `vhd4.vhd` immediately after formatting. This helps keep the fixed-size VHD file contiguous on the disk. After preparing `vhd4.vhd`, rebuild the root folder list so the device can detect and apply the VHD setting. Use one of the following methods to rebuild the root folder list: - Press **Key 1**. - Reboot the device. - Enter a subfolder, then return to the root folder. Behavior when rebuilding the root folder list: | State | Device Behavior | | --------------------------------------- | --------------------------------------------------- | | `vhd4.vhd` exists and is not fragmented | Updates the VHD setting for use with the User 4 PIN | | `vhd4.vhd` exists but is fragmented | Does not apply the VHD setting | | `vhd4.vhd` does not exist | Deletes the saved VHD setting | --- ## 5. What Appears on the PC | State | What the PC Sees | | ------------------------------------------------------ | ------------------------------------------------- | | Unlocked with a PIN other than User 4 | Normal physical partition | | Unlocked with the User 4 PIN, valid `vhd4.vhd` setting | Disk sized to `vhd4.vhd` | | Unlocked with the User 4 PIN, no setting | The VHD disk may not appear | | `vhd4.vhd` is fragmented | The VHD disk may not appear or may not be applied | While unlocked with the User 4 PIN, you cannot see other files from the physical partition. To manage files on the physical partition, unlock again with a PIN other than the User 4 PIN. --- ## 6. Troubleshooting ### The VHD Disk Does Not Appear After Unlocking With the User 4 PIN 1. Unlock the device with a PIN other than the User 4 PIN. 2. Check that `vhd4.vhd` exists in the root folder. 3. Rebuild the root folder list by pressing **Key 1**, rebooting the device, or entering a subfolder and returning to the root folder. 4. Check that `vhd4.vhd` is not fragmented. 5. Unlock again with the User 4 PIN. If the PIN used to update the setting has disk write protection enabled, the VHD setting cannot be updated. ### The Device Does Not Recognize `vhd4.vhd` After It Is Created - Make sure the file name is exactly `vhd4.vhd`. - Make sure the file is in the root folder of the first partition. - Make sure the root folder list was rebuilt after creating the file. Pressing **Key 1**, rebooting the device, or entering a subfolder and returning to the root folder is enough. - A fragmented file cannot be used. ### A Defragmentation or `DEFRAG` Message Appears `vhd4.vhd` is not stored contiguously on the disk. Delete and recreate `vhd4.vhd` on the PC, or arrange it so it is stored in a contiguous area. Then unlock with a PIN other than the User 4 PIN and rebuild the root folder list. --- ## 7. Summary - Place `vhd4.vhd` in the root folder of the first partition. - After creating `vhd4.vhd`, rebuild the root folder list. Pressing **Key 1**, rebooting the device, or entering a subfolder and returning to the root folder is enough. - A PIN other than User 4 is used for file management and VHD setting updates. - A user with disk write protection cannot update the VHD setting. - The User 4 PIN works as the Duress PIN and is used to show the `vhd4.vhd` disk on the PC in Plausible Deniability Mode. - A fragmented `vhd4.vhd` cannot be used.