6 files changed, 1029 insertions, 70 deletions
diff --git a/src/Format/Format.rc b/src/Format/Format.rc
index 44bcc66b..51564a64 100644
--- a/src/Format/Format.rc
+++ b/src/Format/Format.rc
@@ -223,12 +223,12 @@ STYLE DS_SETFONT | DS_FIXEDSYS | DS_CONTROL | WS_CHILD
 FONT 8, "MS Shell Dlg", 0, 0, 0x0
 BEGIN
     EDITTEXT        IDC_PASSWORD_DIRECT,50,2,149,14,ES_PASSWORD | ES_AUTOHSCROLL
+    COMBOBOX        IDC_PKCS5_PRF_ID,50,17,91,90,CBS_DROPDOWNLIST | WS_TABSTOP
     CONTROL         "&Display password",IDC_SHOW_PASSWORD_SINGLE,"Button",BS_AUTOCHECKBOX | WS_TABSTOP,50,31,84,11,WS_EX_TRANSPARENT
     CONTROL         "U&se keyfiles",IDC_KEYFILES_ENABLE,"Button",BS_AUTOCHECKBOX | WS_TABSTOP,50,42,82,11
     PUSHBUTTON      "&Keyfiles...",IDC_KEY_FILES,142,39,64,14
     LTEXT           "",IDC_BOX_HELP,0,57,225,94
     RTEXT           "Password:",IDT_PASSWORD,0,6,48,8
-    COMBOBOX        IDC_PKCS5_PRF_ID,50,17,91,90,CBS_DROPDOWNLIST | WS_TABSTOP
     RTEXT           "PKCS-5 PRF:",IDT_PKCS5_PRF,0,17,48,8
 END
 
@@ -419,6 +419,15 @@ BEGIN
     LISTBOX         IDC_LIST_BOX,0,3,222,100,LBS_NOINTEGRALHEIGHT | LBS_DISABLENOSCROLL | WS_VSCROLL
 END
 
+IDD_DRIVE_LETTER_SELECTION_PAGE DIALOGEX 0, 0, 226, 152
+STYLE DS_SETFONT | DS_FIXEDSYS | DS_CONTROL | WS_CHILD
+FONT 8, "MS Shell Dlg", 400, 0, 0x1
+BEGIN
+    LTEXT           "",IDC_BOX_HELP,0,40,225,95
+    COMBOBOX        IDC_DRIVE_LETTER_LIST,94,15,38,69,CBS_DROPDOWNLIST | WS_VSCROLL | WS_TABSTOP
+    RTEXT           "Drive letter:",IDT_DRIVE_LETTER,5,17,86,8
+END
+
 
 #ifdef APSTUDIO_INVOKED
 /////////////////////////////////////////////////////////////////////////////
@@ -662,6 +671,14 @@ BEGIN
         TOPMARGIN, 7
         BOTTOMMARGIN, 145
     END
+
+    IDD_DRIVE_LETTER_SELECTION_PAGE, DIALOG
+    BEGIN
+        LEFTMARGIN, 7
+        RIGHTMARGIN, 219
+        TOPMARGIN, 7
+        BOTTOMMARGIN, 145
+    END
 END
 #endif    // APSTUDIO_INVOKED
 
diff --git a/src/Format/InPlace.c b/src/Format/InPlace.c
index 3998c2a5..408f6252 100644
--- a/src/Format/InPlace.c
+++ b/src/Format/InPlace.c
@@ -40,6 +40,18 @@ IMPORTANT: Due to this issue, functions in this file must not directly interact
 using namespace std;
 using namespace VeraCrypt;
 
+#if TC_VOLUME_DATA_OFFSET != 131072
+#	error TC_VOLUME_DATA_OFFSET != 131072
+#endif
+
+#if TC_VOLUME_HEADER_EFFECTIVE_SIZE != 512
+#	error TC_VOLUME_HEADER_EFFECTIVE_SIZE != 512
+#endif
+
+#if TC_TOTAL_VOLUME_HEADERS_SIZE != 262144
+#	error TC_TOTAL_VOLUME_HEADERS_SIZE != 262144
+#endif
+
 #define TC_MAX_NONSYS_INPLACE_ENC_WORK_CHUNK_SIZE	(2048 * BYTES_PER_KB)
 #define TC_INITIAL_NTFS_CONCEAL_PORTION_SIZE		(2 * TC_MAX_VOLUME_SECTOR_SIZE)
 #define TC_NTFS_CONCEAL_CONSTANT	0xFF
@@ -312,6 +324,42 @@ BOOL CheckRequirementsForNonSysInPlaceEnc (HWND hwndDlg, const char *devicePath,
 	return TRUE;
 }
 
+BOOL CheckRequirementsForNonSysInPlaceDec (HWND hwndDlg, const char *devicePath, BOOL silent)
+{
+	int partitionNumber = -1, driveNumber = -1;
+
+	/* ---------- Checks that do not require admin rights ----------- */
+
+	/* Volume type (must be a partition or a dynamic volume) */
+	if ((sscanf (devicePath, "\\Device\\HarddiskVolume%d", &partitionNumber) != 1
+		&& sscanf (devicePath, "\\Device\\Harddisk%d\\Partition%d", &driveNumber, &partitionNumber) != 2)
+		|| partitionNumber == 0)
+	{
+		if (!silent)
+			Error ("INPLACE_ENC_INVALID_PATH", hwndDlg);
+
+		return FALSE;
+	}
+
+
+	/* Admin rights */
+	if (!IsAdmin())
+	{
+		// We rely on the wizard process to call us only when the whole wizard process has been elevated (so UAC 
+		// status can be ignored). In case the IsAdmin() detection somehow fails, we allow the user to continue.
+
+		if (!silent)
+			Warning ("ADMIN_PRIVILEGES_WARN_DEVICES", hwndDlg);
+	}
+
+
+	/* ---------- Checks that may require admin rights ----------- */
+
+	// [Currently none]
+
+	return TRUE;
+}
+
 
 int EncryptPartitionInPlaceBegin (volatile FORMAT_VOL_PARAMETERS *volParams, volatile HANDLE *outHandle, WipeAlgorithmId wipeAlgorithm)
 {
@@ -606,7 +654,7 @@ int EncryptPartitionInPlaceBegin (volatile FORMAT_VOL_PARAMETERS *volParams, vol
 
 	// In the config file, increase the number of partitions where in-place encryption is in progress
 
-	SaveNonSysInPlaceEncSettings (1, wipeAlgorithm);
+	SaveNonSysInPlaceEncSettings (1, wipeAlgorithm, FALSE);
 
 
 	// Add the wizard to the system startup sequence if appropriate
@@ -1033,7 +1081,7 @@ inplace_enc_read:
 
 		// Update the configuration files
 
-		SaveNonSysInPlaceEncSettings (-1, wipeAlgorithm);
+		SaveNonSysInPlaceEncSettings (-1, wipeAlgorithm, FALSE);
 
 
 
@@ -1126,6 +1174,513 @@ closing_seq:
 	return nStatus;
 }
 
+int DecryptPartitionInPlace (volatile FORMAT_VOL_PARAMETERS *volParams, volatile BOOL *DiscardUnreadableEncryptedSectors)
+{
+	HANDLE dev = INVALID_HANDLE_VALUE;
+	PCRYPTO_INFO masterCryptoInfo = NULL, headerCryptoInfo = NULL;
+	UINT64_STRUCT unitNo;
+	char *buf = NULL;
+	byte *tmpSectorBuf = NULL;
+	char dosDev[TC_MAX_PATH] = {0};
+	char devName[MAX_PATH] = {0};
+	WCHAR deviceName[MAX_PATH];
+	int nStatus = ERR_SUCCESS;
+	__int64 deviceSize;
+	uint64 remainingBytes, workChunkStartByteOffset, lastHeaderUpdateDistance = 0, skippedBadSectorCount = 0;
+	uint32 workChunkSize;
+	DWORD dwError, dwResult;
+	BOOL bPause = FALSE, bEncryptedAreaSizeChanged = FALSE;
+	LARGE_INTEGER offset;
+	int sectorSize;
+	int i;
+	DWORD n;
+	char *devicePath = volParams->volumePath;
+	Password *password = volParams->password;
+	HWND hwndDlg = volParams->hwndDlg;
+	int pkcs5_prf = volParams->pkcs5;
+	DISK_GEOMETRY driveGeometry;
+
+
+	buf = (char *) TCalloc (TC_MAX_NONSYS_INPLACE_ENC_WORK_CHUNK_SIZE);
+	if (!buf)
+	{
+		nStatus = ERR_OUTOFMEMORY;
+		goto closing_seq;
+	}
+
+	headerCryptoInfo = crypto_open();
+
+	if (headerCryptoInfo == NULL)
+	{
+		nStatus = ERR_OUTOFMEMORY;
+		goto closing_seq;
+	}
+
+	deviceSize = GetDeviceSize (devicePath);
+	if (deviceSize < 0)
+	{
+		// Cannot determine the size of the partition
+		nStatus = ERR_OS_ERROR;
+		goto closing_seq;
+	}
+
+
+	// The wizard should have dismounted the TC volume if it was mounted, but for extra safety we will check this again.
+	if (IsMountedVolume (devicePath))
+	{
+		int driveLetter = GetMountedVolumeDriveNo (devicePath);
+
+		if (driveLetter == -1
+			|| !UnmountVolume (hwndDlg, driveLetter, TRUE))
+		{
+			handleWin32Error (hwndDlg);
+			AbortProcess ("CANT_DISMOUNT_VOLUME");
+		}
+	}
+
+
+	StringCbCopyA ((char *)deviceName, sizeof(deviceName), devicePath);
+	ToUNICODE ((char *)deviceName, sizeof(deviceName));
+
+	if (FakeDosNameForDevice (devicePath, dosDev, sizeof(dosDev), devName, sizeof(devName), FALSE) != 0)
+	{
+		nStatus = ERR_OS_ERROR;
+		goto closing_seq;
+	}
+
+	dev = OpenPartitionVolume (hwndDlg, devName,
+		TRUE,	// Require exclusive access
+		FALSE,	// Do not require shared access
+		TRUE,	// Ask the user to confirm shared access (if exclusive fails)
+		FALSE,	// Do not append alternative instructions how to encrypt the data (to applicable error messages)
+		FALSE);	// Non-silent mode
+
+	if (dev == INVALID_HANDLE_VALUE)
+	{
+		nStatus = ERR_DONT_REPORT; 
+		goto closing_seq;
+	}
+
+
+
+	// This should never be needed, but is still performed for extra safety (without checking the result)
+	DeviceIoControl (dev,
+		FSCTL_ALLOW_EXTENDED_DASD_IO,
+		NULL,
+		0,   
+		NULL,
+		0,
+		&dwResult,
+		NULL);
+
+
+	if (!DeviceIoControl (dev, IOCTL_DISK_GET_DRIVE_GEOMETRY, NULL, 0, &driveGeometry, sizeof (driveGeometry), &dwResult, NULL))
+	{
+		nStatus = ERR_OS_ERROR;
+		goto closing_seq;
+	}
+
+	sectorSize = driveGeometry.BytesPerSector;
+
+
+	tmpSectorBuf = (byte *) TCalloc (sectorSize);
+	if (!tmpSectorBuf)
+	{
+		nStatus = ERR_OUTOFMEMORY;
+		goto closing_seq;
+	}
+
+
+	nStatus = OpenBackupHeader (dev, devicePath, password, pkcs5_prf, &masterCryptoInfo, headerCryptoInfo, deviceSize);
+
+	if (nStatus != ERR_SUCCESS)
+		goto closing_seq;
+
+
+	if (masterCryptoInfo->LegacyVolume)
+	{
+		Error ("NONSYS_INPLACE_DECRYPTION_BAD_VOL_FORMAT", hwndDlg);
+		nStatus = ERR_DONT_REPORT;
+		goto closing_seq;
+	}
+
+	if (masterCryptoInfo->hiddenVolume)
+	{
+		Error ("NONSYS_INPLACE_DECRYPTION_CANT_DECRYPT_HID_VOL", hwndDlg);
+		nStatus = ERR_DONT_REPORT;
+		goto closing_seq;
+	}
+
+	if (!bInPlaceEncNonSysResumed
+		&& masterCryptoInfo->VolumeSize.Value == masterCryptoInfo->EncryptedAreaLength.Value)
+	{
+		/* Decryption started (not resumed) */
+
+		if ((masterCryptoInfo->HeaderFlags & TC_HEADER_FLAG_NONSYS_INPLACE_ENC) == 0)
+		{
+			// The volume has not been encrypted in-place so it may contain a hidden volume.
+			// Ask the user to confirm it does not.
+
+			char *tmpStr[] = {0,
+				"CONFIRM_VOL_CONTAINS_NO_HIDDEN_VOL",
+				"VOL_CONTAINS_NO_HIDDEN_VOL",
+				"VOL_CONTAINS_A_HIDDEN_VOL",
+				0};
+
+			switch (AskMultiChoice ((void **) tmpStr, FALSE, hwndDlg))
+			{
+			case 1:
+				// NOP 
+				break;
+			case 2:
+			default:
+				// Cancel
+				nStatus = ERR_DONT_REPORT;
+				goto closing_seq;
+			}
+		}
+
+		// Update config files and app data
+
+		// In the config file, increase the number of partitions where in-place decryption is in progress
+		SaveNonSysInPlaceEncSettings (1, TC_WIPE_NONE, TRUE);
+
+		// Add the wizard to the system startup sequence if appropriate
+		if (!IsNonInstallMode ())
+			ManageStartupSeqWiz (FALSE, "/prinplace");
+	}
+
+
+
+	bInPlaceEncNonSysResumed = TRUE;
+	bFirstNonSysInPlaceEncResumeDone = TRUE;
+
+
+	remainingBytes = masterCryptoInfo->EncryptedAreaLength.Value;
+
+	lastHeaderUpdateDistance = 0;
+
+
+	ExportProgressStats (masterCryptoInfo->EncryptedAreaLength.Value, masterCryptoInfo->VolumeSize.Value);
+
+	SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_DECRYPTING);
+
+
+
+	/* The in-place decryption core */
+
+	while (remainingBytes > 0)
+	{
+		workChunkSize = (uint32) min (remainingBytes, TC_MAX_NONSYS_INPLACE_ENC_WORK_CHUNK_SIZE);
+
+		if (workChunkSize % ENCRYPTION_DATA_UNIT_SIZE != 0)
+		{
+			nStatus = ERR_PARAMETER_INCORRECT;
+			goto closing_seq;
+		}
+
+		workChunkStartByteOffset = masterCryptoInfo->EncryptedAreaStart.Value;
+
+		unitNo.Value = workChunkStartByteOffset / ENCRYPTION_DATA_UNIT_SIZE;
+
+
+		// Read the ciphertext into RAM
+
+		offset.QuadPart = workChunkStartByteOffset;
+
+		if (SetFilePointerEx (dev, offset, NULL, FILE_BEGIN) == 0)
+		{
+			nStatus = ERR_OS_ERROR;
+			goto closing_seq;
+		}
+
+		if (ReadFile (dev, buf, workChunkSize, &n, NULL) == 0)
+		{
+			// Read error
+
+			DWORD dwTmpErr = GetLastError ();
+
+			if (IsDiskReadError (dwTmpErr) && !bVolTransformThreadCancel)
+			{
+				// Physical defect or data corruption
+
+				if (!*DiscardUnreadableEncryptedSectors)
+				{
+					*DiscardUnreadableEncryptedSectors = (AskWarnYesNo ("DISCARD_UNREADABLE_ENCRYPTED_SECTORS", hwndDlg) == IDYES);
+				}
+
+				if (*DiscardUnreadableEncryptedSectors)
+				{
+					// Read the work chunk again, but this time each sector individually and skiping each bad sector
+
+					LARGE_INTEGER tmpSectorOffset;
+					uint64 tmpSectorCount;
+					uint64 tmpBufOffset = 0;
+					DWORD tmpNbrReadBytes = 0;
+
+					tmpSectorOffset.QuadPart = offset.QuadPart;
+
+					for (tmpSectorCount = workChunkSize / sectorSize; tmpSectorCount > 0; --tmpSectorCount)
+					{
+						if (SetFilePointerEx (dev, tmpSectorOffset, NULL, FILE_BEGIN) == 0)
+						{
+							nStatus = ERR_OS_ERROR;
+							goto closing_seq;
+						}
+
+						if (ReadFile (dev, tmpSectorBuf, sectorSize, &tmpNbrReadBytes, NULL) == 0
+							|| tmpNbrReadBytes != (DWORD) sectorSize)
+						{
+							// Read error
+
+							// Clear the buffer so the content of each unreadable sector is replaced with decrypted all-zero blocks (producing pseudorandom data)
+							memset (tmpSectorBuf, 0, sectorSize);
+
+							skippedBadSectorCount++;
+						}
+
+						memcpy (buf + tmpBufOffset, tmpSectorBuf, sectorSize);
+
+						tmpSectorOffset.QuadPart += sectorSize;
+						tmpBufOffset += sectorSize;
+					}
+				}
+				else
+				{
+					SetLastError (dwTmpErr);		// Preserve the original error code
+
+					nStatus = ERR_OS_ERROR;
+					goto closing_seq;
+				}
+			}
+			else
+			{
+				SetLastError (dwTmpErr);		// Preserve the original error code
+
+				nStatus = ERR_OS_ERROR;
+				goto closing_seq;
+			}
+		}
+		
+		// Decrypt the ciphertext in RAM
+
+		DecryptDataUnits ((byte *) buf, &unitNo, workChunkSize / ENCRYPTION_DATA_UNIT_SIZE, masterCryptoInfo);
+
+
+
+		// Conceal initial portion of the filesystem
+
+		if (workChunkStartByteOffset - TC_VOLUME_DATA_OFFSET < TC_INITIAL_NTFS_CONCEAL_PORTION_SIZE)
+		{
+			// We are decrypting the initial TC_INITIAL_NTFS_CONCEAL_PORTION_SIZE bytes of the filesystem. We will 
+			// conceal this portion to prevent Windows and applications from interfering with the volume.
+
+			for (i = 0; i < min (TC_INITIAL_NTFS_CONCEAL_PORTION_SIZE, workChunkStartByteOffset - TC_VOLUME_DATA_OFFSET + workChunkSize); i++)
+				buf[i] ^= TC_NTFS_CONCEAL_CONSTANT;
+		}
+
+
+		// Write the plaintext
+
+		offset.QuadPart = workChunkStartByteOffset - TC_VOLUME_DATA_OFFSET;
+
+		if (SetFilePointerEx (dev, offset, NULL, FILE_BEGIN) == 0)
+		{
+			nStatus = ERR_OS_ERROR;
+			goto closing_seq;
+		}
+
+		if (WriteFile (dev, buf, workChunkSize, &n, NULL) == 0)
+		{
+			// Write error
+			nStatus = ERR_OS_ERROR;
+			goto closing_seq;
+		}
+
+
+		masterCryptoInfo->EncryptedAreaStart.Value += workChunkSize;
+		masterCryptoInfo->EncryptedAreaLength.Value -= workChunkSize;
+
+		remainingBytes -= workChunkSize;
+		lastHeaderUpdateDistance += workChunkSize;
+
+		bEncryptedAreaSizeChanged = TRUE;
+
+		if (lastHeaderUpdateDistance >= TC_NONSYS_INPLACE_ENC_HEADER_UPDATE_INTERVAL)
+		{
+			nStatus = FastVolumeHeaderUpdate (dev, headerCryptoInfo, masterCryptoInfo, deviceSize);
+
+			if (nStatus != ERR_SUCCESS)
+			{
+				// Possible write error
+				goto closing_seq;
+			}
+
+			lastHeaderUpdateDistance = 0;
+		}
+
+		ExportProgressStats (masterCryptoInfo->EncryptedAreaLength.Value, masterCryptoInfo->VolumeSize.Value);
+
+		if (bVolTransformThreadCancel)
+		{
+			bPause = TRUE;
+			break;
+		}
+	}
+
+	nStatus = FastVolumeHeaderUpdate (dev, headerCryptoInfo, masterCryptoInfo, deviceSize);
+
+
+	if (nStatus != ERR_SUCCESS)
+	{
+		// Possible write error
+		goto closing_seq;
+	}
+
+
+	if (!bPause)
+	{
+		/* Volume has been fully decrypted. */
+
+
+		// Prevent attempts to update volume header during the closing sequence
+		bEncryptedAreaSizeChanged = FALSE;
+
+
+		SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_FINALIZING);
+
+
+
+		/* Undo concealing of the filesystem */
+
+		nStatus = ConcealNTFS (dev);
+
+		if (nStatus != ERR_SUCCESS)
+			goto closing_seq;
+
+
+
+		/* Ovewrite the backup header and the remaining ciphertext with all-zero blocks (the primary header was overwritten with the decrypted data). */
+
+		memset (tmpSectorBuf, 0, sectorSize);
+
+		for (offset.QuadPart = masterCryptoInfo->VolumeSize.Value;
+			offset.QuadPart <= deviceSize - sectorSize;
+			offset.QuadPart += sectorSize)
+		{
+			if (SetFilePointerEx (dev, offset, NULL, FILE_BEGIN) == 0)
+			{
+				nStatus = ERR_OS_ERROR;
+				goto closing_seq;
+			}
+
+			if (WriteFile (dev, tmpSectorBuf, sectorSize, &n, NULL) == 0)
+			{
+				// Write error
+				dwError = GetLastError();
+
+				SetLastError (dwError);
+				nStatus = ERR_OS_ERROR;
+				goto closing_seq;
+			}
+		}
+
+
+
+		/* Update the configuration files */
+
+		SaveNonSysInPlaceEncSettings (-1, TC_WIPE_NONE, TRUE);
+
+
+
+		SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_FINISHED);
+
+		nStatus = ERR_SUCCESS;
+
+	}
+	else
+	{
+		// The process has been paused by the user or aborted by the wizard (e.g. on app exit)
+
+		nStatus = ERR_USER_ABORT;
+
+		SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_PAUSED);
+	}
+
+	if (dev != INVALID_HANDLE_VALUE)
+	{
+		CloseHandle (dev);
+		dev = INVALID_HANDLE_VALUE;
+	}
+
+
+closing_seq:
+
+	dwError = GetLastError();
+
+	if (bEncryptedAreaSizeChanged
+		&& dev != INVALID_HANDLE_VALUE
+		&& masterCryptoInfo != NULL
+		&& headerCryptoInfo != NULL
+		&& deviceSize > 0)
+	{
+		// Execution of the core loop may have been interrupted due to an error or user action without updating the header
+		FastVolumeHeaderUpdate (dev, headerCryptoInfo, masterCryptoInfo, deviceSize);
+	}
+
+	if (dev != INVALID_HANDLE_VALUE)
+	{
+		CloseHandle (dev);
+		dev = INVALID_HANDLE_VALUE;
+	}
+
+	if (masterCryptoInfo != NULL)
+	{
+		crypto_close (masterCryptoInfo);
+		masterCryptoInfo = NULL;
+	}
+
+	if (headerCryptoInfo != NULL)
+	{
+		crypto_close (headerCryptoInfo);
+		headerCryptoInfo = NULL;
+	}
+
+	if (dosDev[0])
+		RemoveFakeDosName (devicePath, dosDev);
+
+	if (buf != NULL)
+	{
+		TCfree (buf);
+		buf = NULL;
+	}
+
+	if (tmpSectorBuf != NULL)
+	{
+		TCfree (tmpSectorBuf);
+		tmpSectorBuf = NULL;
+	}
+
+	if (skippedBadSectorCount > 0)
+	{
+		wchar_t msg[30000] = {0};
+		wchar_t sizeStr[500] = {0};
+
+		GetSizeString (skippedBadSectorCount * sectorSize, sizeStr, sizeof(sizeStr));
+
+		StringCbPrintfW (msg, sizeof(msg),
+			GetString ("SKIPPED_BAD_SECTOR_COUNT"),
+			skippedBadSectorCount,
+			sizeStr);
+
+		WarningDirect (msg, hwndDlg);
+	}
+
+	if (nStatus != ERR_SUCCESS && nStatus != ERR_USER_ABORT)
+		SetLastError (dwError);
+
+	return nStatus;
+}
 
 int FastVolumeHeaderUpdate (HANDLE dev, CRYPTO_INFO *headerCryptoInfo, CRYPTO_INFO *masterCryptoInfo, __int64 deviceSize)
 {
@@ -1168,6 +1723,13 @@ int FastVolumeHeaderUpdate (HANDLE dev, CRYPTO_INFO *headerCryptoInfo, CRYPTO_IN
 	mputInt64 (fieldPos, (masterCryptoInfo->EncryptedAreaStart.Value));
 	mputInt64 (fieldPos, (masterCryptoInfo->EncryptedAreaLength.Value));
 
+	// We need to ensure the TC_HEADER_FLAG_NONSYS_INPLACE_ENC flag bit is set, because if volumes created by TC-format
+	// were decrypted in place, it would be possible to mount them partially encrypted and it wouldn't be possible
+	// to resume interrupted decryption after the wizard exits.
+	masterCryptoInfo->HeaderFlags |= TC_HEADER_FLAG_NONSYS_INPLACE_ENC;
+	fieldPos = (byte *) header + TC_HEADER_OFFSET_FLAGS;
+	mputLong (fieldPos, (masterCryptoInfo->HeaderFlags));
+
 
 	headerCrc32 = GetCrc32 (header + TC_HEADER_OFFSET_MAGIC, TC_HEADER_OFFSET_HEADER_CRC - TC_HEADER_OFFSET_MAGIC);
 	fieldPos = (byte *) header + TC_HEADER_OFFSET_HEADER_CRC;
@@ -1419,7 +1981,7 @@ void SetNonSysInplaceEncUIStatus (int nonSysInplaceEncStatus)
 }
 
 
-BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId newWipeAlgorithm)
+BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId newWipeAlgorithm, BOOL bDecrypt)
 {
 	int count;
 	char str[32];
@@ -1435,7 +1997,7 @@ BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId newWipeAlgorithm)
 		RemoveNonSysInPlaceEncNotifications();
 		return TRUE;
 	}
-	else
+	else if (!bDecrypt)
 	{
 		if (newWipeAlgorithm != TC_WIPE_NONE)
 		{
@@ -1447,11 +2009,11 @@ BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId newWipeAlgorithm)
 		{
 			remove (GetConfigPath (TC_APPD_FILENAME_NONSYS_INPLACE_ENC_WIPE));
 		}
-
-		StringCbPrintfA (str, sizeof(str), "%d", count);
-
-		return SaveBufferToFile (str, GetConfigPath (TC_APPD_FILENAME_NONSYS_INPLACE_ENC), strlen(str), FALSE);
 	}
+	
+	StringCbPrintfA (str, sizeof(str), "%d", count);
+
+	return SaveBufferToFile (str, GetConfigPath (TC_APPD_FILENAME_NONSYS_INPLACE_ENC), strlen(str), FALSE);
 }
 
 
diff --git a/src/Format/InPlace.h b/src/Format/InPlace.h
index 90cf5f80..6b59bbd4 100644
--- a/src/Format/InPlace.h
+++ b/src/Format/InPlace.h
@@ -18,6 +18,7 @@ enum nonsys_inplace_enc_status
 	NONSYS_INPLACE_ENC_STATUS_PREPARING,
 	NONSYS_INPLACE_ENC_STATUS_RESIZING,
 	NONSYS_INPLACE_ENC_STATUS_ENCRYPTING,
+	NONSYS_INPLACE_ENC_STATUS_DECRYPTING,
 	NONSYS_INPLACE_ENC_STATUS_FINALIZING,
 	NONSYS_INPLACE_ENC_STATUS_PAUSED,
 	NONSYS_INPLACE_ENC_STATUS_FINISHED,
@@ -25,8 +26,10 @@ enum nonsys_inplace_enc_status
 };
 
 BOOL CheckRequirementsForNonSysInPlaceEnc (HWND hwndDlg, const char *devicePath, BOOL silent);
+BOOL CheckRequirementsForNonSysInPlaceDec (HWND hwndDlg, const char *devicePath, BOOL silent);
 int EncryptPartitionInPlaceBegin (volatile FORMAT_VOL_PARAMETERS *volParams, volatile HANDLE *outHandle, WipeAlgorithmId wipeAlgorithm);
 int EncryptPartitionInPlaceResume (HANDLE dev, volatile FORMAT_VOL_PARAMETERS *volParams, WipeAlgorithmId wipeAlgorithm, volatile BOOL *bTryToCorrectReadErrors);
+int DecryptPartitionInPlace (volatile FORMAT_VOL_PARAMETERS *volParams, volatile BOOL *DiscardUnreadableEncryptedSectors);
 void ShowInPlaceEncErrMsgWAltSteps (HWND hwndDlg, char *iniStrId, BOOL bErr);
 void SetNonSysInplaceEncUIStatus (int nonSysInplaceEncStatus);
 int FastVolumeHeaderUpdate (HANDLE dev, CRYPTO_INFO *headerCryptoInfo, CRYPTO_INFO *masterCryptoInfo, __int64 deviceSize);
@@ -34,7 +37,7 @@ int FastVolumeHeaderUpdate (HANDLE dev, CRYPTO_INFO *headerCryptoInfo, CRYPTO_IN
 static HANDLE OpenPartitionVolume (HWND hwndDlg, const char *devName, BOOL bExclusiveRequired, BOOL bSharedRequired, BOOL bSharedRequiresConfirmation, BOOL bShowAlternativeSteps, BOOL bSilent);
 static int DismountFileSystem (HWND hwndDlg, HANDLE dev, int driveLetter, BOOL bForcedAllowed, BOOL bForcedRequiresConfirmation, BOOL bSilent);
 static int ConcealNTFS (HANDLE dev);
-BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId wipeAlgorithm);
+BOOL SaveNonSysInPlaceEncSettings (int delta, WipeAlgorithmId wipeAlgorithm, BOOL bDecrypting);
 static void ExportProgressStats (__int64 bytesDone, __int64 totalSize);
 int ZeroUnreadableSectors (HANDLE dev, LARGE_INTEGER startOffset, int64 size, int sectorSize, uint64 *zeroedSectorCount);
 static int OpenBackupHeader (HANDLE dev, const char *devicePath, Password *password, int pkcs5, PCRYPTO_INFO *retCryptoInfo, CRYPTO_INFO *headerCryptoInfo, __int64 deviceSize);
diff --git a/src/Format/Resource.h b/src/Format/Resource.h
index 61a38332..feba5ec3 100644
--- a/src/Format/Resource.h
+++ b/src/Format/Resource.h
@@ -34,6 +34,7 @@
 #define IDD_DEVICE_WIPE_MODE_PAGE_DLG   129
 #define IDD_DEVICE_TRANSFORM_MODE_DLG   130
 #define IDD_EXPANDED_LIST_SELECT_PAGE_DLG 131
+#define IDD_DRIVE_LETTER_SELECTION_PAGE 132
 #define IDC_BOX_TITLE                   1000
 #define IDC_RESCUE_DISK_ISO_PATH        1001
 #define IDC_COMBO_BOX                   1002
@@ -137,15 +138,17 @@
 #define IDT_PASS                        1100
 #define IDC_DEVICE_TRANSFORM_MODE_FORMAT 1101
 #define IDC_DEVICE_TRANSFORM_MODE_INPLACE 1102
+#define IDC_DRIVE_LETTER_LIST			1103
+#define IDT_DRIVE_LETTER				1104
 
 // Next default values for new objects
 // 
 #ifdef APSTUDIO_INVOKED
 #ifndef APSTUDIO_READONLY_SYMBOLS
 #define _APS_NO_MFC                     1
-#define _APS_NEXT_RESOURCE_VALUE        132
+#define _APS_NEXT_RESOURCE_VALUE        133
 #define _APS_NEXT_COMMAND_VALUE         40001
-#define _APS_NEXT_CONTROL_VALUE         1103
+#define _APS_NEXT_CONTROL_VALUE         1105
 #define _APS_NEXT_SYMED_VALUE           101
 #endif
 #endif
diff --git a/src/Format/Tcformat.c b/src/Format/Tcformat.c
index ba35c47e..a0d9b293 100644
--- a/src/Format/Tcformat.c
+++ b/src/Format/Tcformat.c
@@ -94,8 +94,9 @@ enum wizard_pages
 		NONSYS_INPLACE_ENC_RESUME_PARTITION_SEL_PAGE,
 		NONSYS_INPLACE_ENC_RAND_DATA_PAGE,
 		NONSYS_INPLACE_ENC_WIPE_MODE_PAGE,
-		NONSYS_INPLACE_ENC_ENCRYPTION_PAGE,
-		NONSYS_INPLACE_ENC_ENCRYPTION_FINISHED_PAGE,
+		NONSYS_INPLACE_ENC_TRANSFORM_PAGE,
+		NONSYS_INPLACE_ENC_TRANSFORM_FINISHED_PAGE,
+		NONSYS_INPLACE_DEC_TRANSFORM_FINISHED_DRIVE_LETTER_PAGE,
 	FORMAT_PAGE,
 	FORMAT_FINISHED_PAGE,
 					SYSENC_HIDDEN_OS_INITIAL_INFO_PAGE,
@@ -148,10 +149,13 @@ volatile BOOL bHiddenOS = FALSE;		/* If TRUE, we are performing or (or supposed
 BOOL bDirectSysEncMode = FALSE;
 BOOL bDirectSysEncModeCommand = SYSENC_COMMAND_NONE;
 BOOL DirectDeviceEncMode = FALSE;
+BOOL DirectNonSysInplaceDecStartMode = FALSE;
 BOOL DirectNonSysInplaceEncResumeMode = FALSE;
+BOOL DirectNonSysInplaceDecResumeMode = FALSE;
 BOOL DirectPromptNonSysInplaceEncResumeMode = FALSE;
-volatile BOOL bInPlaceEncNonSys = FALSE;		/* If TRUE, existing data on a non-system partition/volume are to be encrypted (for system encryption, this flag is ignored) */
-volatile BOOL bInPlaceEncNonSysResumed = FALSE;	/* If TRUE, the wizard is supposed to resume (or has resumed) process of non-system in-place encryption. */
+volatile BOOL bInPlaceEncNonSys = FALSE;		/* If TRUE, existing data on a non-system partition/volume are to be encrypted (or decrypted if bInPlaceDecNonSys is TRUE) in place (for system encryption, this flag is ignored) */
+volatile BOOL bInPlaceDecNonSys = FALSE;		/* If TRUE, existing data on a non-system partition/volume are to be decrypted in place (for system encryption, this flag is ignored) */
+volatile BOOL bInPlaceEncNonSysResumed = FALSE;	/* If TRUE, the wizard is supposed to resume (or has resumed) process of non-system in-place encryption/decryption. */
 volatile BOOL bFirstNonSysInPlaceEncResumeDone = FALSE;
 __int64 NonSysInplaceEncBytesDone = 0;
 __int64 NonSysInplaceEncTotalSize = 0;
@@ -657,7 +661,10 @@ static BOOL ChangeWizardMode (int newWizardMode)
 		}
 
 		if (newWizardMode != WIZARD_MODE_NONSYS_DEVICE)
+		{
 			bInPlaceEncNonSys = FALSE;
+			bInPlaceDecNonSys = FALSE;
+		}
 
 		if (newWizardMode == WIZARD_MODE_NONSYS_DEVICE && !IsAdmin() && IsUacSupported())
 		{
@@ -666,7 +673,8 @@ static BOOL ChangeWizardMode (int newWizardMode)
 		}
 
 		// The contents of the following items may be inappropriate after a change of mode
-		szFileName[0] = 0;
+		if (! (bInPlaceDecNonSys && !bInPlaceEncNonSysResumed))	// If we are starting (but not resuming) decryption of non-system volume, we actually need szFileName as it contains the command line param.
+			szFileName[0] = 0;
 		szDiskFile[0] = 0;
 		nUIVolumeSize = 0;
 		nVolumeSize = 0;
@@ -1067,6 +1075,7 @@ BOOL SwitchWizardToHiddenOSMode (void)
 			bHiddenVolDirect = FALSE;
 			bWholeSysDrive = FALSE;
 			bInPlaceEncNonSys = FALSE;
+			bInPlaceDecNonSys = FALSE;
 
 			if (bDirectSysEncModeCommand == SYSENC_COMMAND_CREATE_HIDDEN_OS_ELEV)
 			{
@@ -1102,11 +1111,11 @@ BOOL SwitchWizardToHiddenOSMode (void)
 	return TRUE;
 }
 
-void SwitchWizardToNonSysInplaceEncResumeMode (void)
+void SwitchWizardToNonSysInplaceEncResumeMode (BOOL bDecrypt)
 {
 	if (!IsAdmin() && IsUacSupported())
 	{
-		if (!ElevateWholeWizardProcess ("/zinplace"))
+		if (!ElevateWholeWizardProcess (bDecrypt ? "/resumeinplacedec" : "/zinplace"))
 			AbortProcessSilent ();
 	}
 
@@ -1116,6 +1125,7 @@ void SwitchWizardToNonSysInplaceEncResumeMode (void)
 	CreateNonSysInplaceEncMutex ();
 
 	bInPlaceEncNonSys = TRUE;
+	bInPlaceDecNonSys = bDecrypt;
 	bInPlaceEncNonSysResumed = TRUE;
 
 	ChangeWizardMode (WIZARD_MODE_NONSYS_DEVICE);
@@ -1123,6 +1133,31 @@ void SwitchWizardToNonSysInplaceEncResumeMode (void)
 	LoadPage (MainDlg, NONSYS_INPLACE_ENC_RESUME_PASSWORD_PAGE);
 }
 
+void SwitchWizardToNonSysInplaceDecStartMode (char *volPath)
+{
+	if (!IsAdmin() && IsUacSupported())
+	{
+		if (!ElevateWholeWizardProcess ((string ("/inplacedec \"") + volPath + "\"").c_str()))
+			AbortProcessSilent ();
+	}
+
+	if (!IsAdmin())
+		AbortProcess("ADMIN_PRIVILEGES_WARN_DEVICES");
+
+	if (!CheckRequirementsForNonSysInPlaceDec (MainDlg, volPath, FALSE))
+		AbortProcessSilent ();
+
+	CreateNonSysInplaceEncMutex ();
+
+	bInPlaceEncNonSys = TRUE;
+	bInPlaceDecNonSys = TRUE;
+	bInPlaceEncNonSysResumed = FALSE;
+
+	ChangeWizardMode (WIZARD_MODE_NONSYS_DEVICE);
+
+	LoadPage (MainDlg, NONSYS_INPLACE_ENC_RESUME_PASSWORD_PAGE);
+}
+
 // Use this function e.g. if the config file with the system encryption settings was lost or not written
 // correctly, and we don't know whether to encrypt or decrypt (but we know that encryption or decryption
 // is required). Returns FALSE if failed or cancelled.
@@ -1730,6 +1765,7 @@ static void SysEncResume (void)
 			return;
 		}
 
+		bVolTransformThreadCancel = FALSE;
 		bSystemEncryptionInProgress = FALSE;
 		WaitCursor ();
 
@@ -1906,6 +1942,9 @@ void ShowNonSysInPlaceEncUIStatus (void)
 	case NONSYS_INPLACE_ENC_STATUS_ENCRYPTING:
 		StringCbCopyW (nonSysInplaceEncUIStatus, sizeof(nonSysInplaceEncUIStatus), GetString ("PROGRESS_STATUS_ENCRYPTING"));
 		break;
+	case NONSYS_INPLACE_ENC_STATUS_DECRYPTING:
+		StringCbCopyW (nonSysInplaceEncUIStatus, sizeof(nonSysInplaceEncUIStatus), GetString ("PROGRESS_STATUS_DECRYPTING"));
+		break;
 	case NONSYS_INPLACE_ENC_STATUS_FINALIZING:
 		StringCbCopyW (nonSysInplaceEncUIStatus, sizeof(nonSysInplaceEncUIStatus), GetString ("PROGRESS_STATUS_FINALIZING"));
 		break;
@@ -1925,12 +1964,28 @@ void ShowNonSysInPlaceEncUIStatus (void)
 
 void UpdateNonSysInPlaceEncControls (void)
 {
-	EnableWindow (GetDlgItem (hCurPage, IDC_WIPE_MODE), !(bVolTransformThreadRunning || bVolTransformThreadToRun));
+	// Reduce flickering by updating a GUI element only when a relevant change affects it
+	static BOOL lastbVolTransformThreadRunning = !bVolTransformThreadRunning;
+	static BOOL lastbVolTransformThreadToRun = !bVolTransformThreadToRun;
+	static BOOL lastbInPlaceEncNonSysResumed = !bInPlaceEncNonSysResumed;
 
-	SetWindowTextW (GetDlgItem (hCurPage, IDC_PAUSE),
-		GetString ((bVolTransformThreadRunning || bVolTransformThreadToRun) ? "IDC_PAUSE" : "RESUME"));
+	EnableWindow (GetDlgItem (hCurPage, IDC_WIPE_MODE), !(bVolTransformThreadRunning || bVolTransformThreadToRun) && !bInPlaceDecNonSys);
+
+	if (lastbVolTransformThreadRunning != bVolTransformThreadRunning
+		|| lastbVolTransformThreadToRun != bVolTransformThreadToRun)
+	{
+		SetWindowTextW (GetDlgItem (hCurPage, IDC_PAUSE),
+			GetString ((bVolTransformThreadRunning || bVolTransformThreadToRun) ? "IDC_PAUSE" : "RESUME"));
 
-	SetWindowTextW (GetDlgItem (MainDlg, IDCANCEL), GetString (bInPlaceEncNonSysResumed ? "DEFER" : "CANCEL"));
+		lastbVolTransformThreadRunning = bVolTransformThreadRunning;
+		lastbVolTransformThreadToRun = bVolTransformThreadToRun;
+	}
+
+	if (lastbInPlaceEncNonSysResumed != bInPlaceEncNonSysResumed)
+	{
+		SetWindowTextW (GetDlgItem (MainDlg, IDCANCEL), GetString (bInPlaceEncNonSysResumed ? "DEFER" : "CANCEL"));
+		lastbInPlaceEncNonSysResumed = bInPlaceEncNonSysResumed;
+	}
 
 	EnableWindow (GetDlgItem (hCurPage, IDC_PAUSE), bFirstNonSysInPlaceEncResumeDone 
 		&& NonSysInplaceEncStatus != NONSYS_INPLACE_ENC_STATUS_FINALIZING
@@ -1995,11 +2050,12 @@ static void UpdateNonSysInplaceEncProgressBar (void)
 
 	if (bVolTransformThreadRunning 
 		&& (nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_ENCRYPTING
+		|| nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_DECRYPTING
 		|| nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_FINALIZING
 		|| nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_FINISHED))
 	{
 		if (lastNonSysInplaceEncStatus != nonSysInplaceEncStatus
-			&& nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_ENCRYPTING)
+			&& (nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_ENCRYPTING || nonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_DECRYPTING))
 		{
 			InitNonSysInplaceEncProgressBar ();
 		}
@@ -2033,7 +2089,7 @@ static void InitNonSysInplaceEncProgressBar (void)
 
 	InitProgressBar (totalSize,
 		NonSysInplaceEncBytesDone,
-		FALSE,
+		bInPlaceDecNonSys,
 		TRUE,
 		TRUE,
 		TRUE);
@@ -2436,7 +2492,7 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 	volParams->hiddenVolHostSize = nHiddenVolHostSize;
 	volParams->ea = nVolumeEA;
 	volParams->pkcs5 = hash_algo;
-	volParams->headerFlags = CreatingHiddenSysVol() ? TC_HEADER_FLAG_ENCRYPTED_SYSTEM : 0;
+	volParams->headerFlags = (CreatingHiddenSysVol() ? TC_HEADER_FLAG_ENCRYPTED_SYSTEM : 0);
 	volParams->fileSystem = fileSystem;
 	volParams->clusterSize = clusterSize;
 	volParams->sparseFileSwitch = bSparseFileSwitch;
@@ -2446,8 +2502,19 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 	volParams->password = &volumePassword;
 	volParams->hwndDlg = hwndDlg;
 
-	if (bInPlaceEncNonSys)
+	if (bInPlaceDecNonSys)
 	{
+		// In-place decryption of non-system volume
+
+		if (!bInPlaceEncNonSysResumed)
+			DiscardUnreadableEncryptedSectors = FALSE;
+
+		nStatus = DecryptPartitionInPlace (volParams, &DiscardUnreadableEncryptedSectors);
+	}
+	else if (bInPlaceEncNonSys)
+	{
+		// In-place encryption of non-system volume
+
 		HANDLE hPartition = INVALID_HANDLE_VALUE;
 
 		SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_PREPARING);
@@ -2475,6 +2542,8 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 	}
 	else
 	{
+		// Format-encryption
+
 		InitProgressBar (GetVolumeDataAreaSize (bHidden, nVolumeSize), 0, FALSE, FALSE, FALSE, TRUE);
 
 		nStatus = TCFormatVolume (volParams);
@@ -2492,7 +2561,7 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 		&& nStatus == ERR_USER_ABORT
 		&& NonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_FINISHED)
 	{
-		// Ignore user abort if non-system in-place encryption successfully finished
+		// Ignore user abort if non-system in-place encryption/decryption successfully finished
 		nStatus = ERR_SUCCESS;
 	}
 
@@ -2519,7 +2588,7 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 	SetLastError (dwWin32FormatError);
 
 	if ((bVolTransformThreadCancel || nStatus == ERR_USER_ABORT)
-		&& !(bInPlaceEncNonSys && NonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_FINISHED))	// Ignore user abort if non-system in-place encryption successfully finished.
+		&& !(bInPlaceEncNonSys && NonSysInplaceEncStatus == NONSYS_INPLACE_ENC_STATUS_FINISHED))	// Ignore user abort if non-system in-place encryption/decryption successfully finished.
 	{
 		if (!bDevice && !(bHiddenVol && !bHiddenVolHost))	// If we're not creating a hidden volume and if it's a file container
 		{
@@ -2549,7 +2618,11 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 				else
 				{
 					SetNonSysInplaceEncUIStatus (NONSYS_INPLACE_ENC_STATUS_ERROR);
-					ShowInPlaceEncErrMsgWAltSteps (hwndDlg, "INPLACE_ENC_GENERIC_ERR_ALT_STEPS", TRUE);
+
+					if (bInPlaceDecNonSys)
+						Error ("INPLACE_DEC_GENERIC_ERR", hwndDlg);
+					else
+						ShowInPlaceEncErrMsgWAltSteps (hwndDlg, "INPLACE_ENC_GENERIC_ERR_ALT_STEPS", TRUE);
 				}
 			}
 			else if (!(bHiddenVolHost && hiddenVolHostDriveNo < 0))  // If the error was not that the hidden volume host could not be mounted (this error has already been reported to the user)
@@ -2589,9 +2662,16 @@ static void __cdecl volTransformThreadFunction (void *hwndDlgArg)
 				}
 				else if (bInPlaceEncNonSys)
 				{
-					Warning ("NONSYS_INPLACE_ENC_FINISHED_INFO", hwndDlg);
+					if (!bInPlaceDecNonSys)
+					{
+						Warning ("NONSYS_INPLACE_ENC_FINISHED_INFO", hwndDlg);
 
-					HandleOldAssignedDriveLetter ();
+						HandleOldAssignedDriveLetter ();
+					}
+					else
+					{
+						// NOP - Final steps for in-place decryption are handled with the TC_APPMSG_NONSYS_INPLACE_ENC_FINISHED message.
+					}
 				}
 				else 
 				{
@@ -2868,16 +2948,21 @@ static void LoadPage (HWND hwndDlg, int nPageNo)
 			(DLGPROC) PageDialogProc);
 		break;
 
-	case NONSYS_INPLACE_ENC_ENCRYPTION_PAGE:
+	case NONSYS_INPLACE_ENC_TRANSFORM_PAGE:
 		hCurPage = CreateDialogW (hInst, MAKEINTRESOURCEW (IDD_INPLACE_ENCRYPTION_PAGE_DLG), hwndDlg,
 			(DLGPROC) PageDialogProc);
 		break;
 
-	case NONSYS_INPLACE_ENC_ENCRYPTION_FINISHED_PAGE:
+	case NONSYS_INPLACE_ENC_TRANSFORM_FINISHED_PAGE:
 		hCurPage = CreateDialogW (hInst, MAKEINTRESOURCEW (IDD_INFO_PAGE_DLG), hwndDlg,
 					 (DLGPROC) PageDialogProc);
 		break;
 
+	case NONSYS_INPLACE_DEC_TRANSFORM_FINISHED_DRIVE_LETTER_PAGE:
+		hCurPage = CreateDialogW (hInst, MAKEINTRESOURCEW (IDD_DRIVE_LETTER_SELECTION_PAGE), hwndDlg,
+			(DLGPROC) PageDialogProc);
+		break;
+
 	case FORMAT_PAGE:
 		hCurPage = CreateDialogW (hInst, MAKEINTRESOURCEW (IDD_FORMAT_PAGE_DLG), hwndDlg,
 					 (DLGPROC) PageDialogProc);
@@ -3272,7 +3357,7 @@ static BOOL FinalPreTransformPrompts (void)
 		if (bHiddenOS && bHiddenVolHost)
 			StringCbPrintfW (szTmp, sizeof(szTmp), GetString ("OVERWRITEPROMPT_DEVICE_HIDDEN_OS_PARTITION"), szFileName, drive);
 		else
-			StringCbPrintfW (szTmp, sizeof(szTmp), GetString (bInPlaceEncNonSys ? "NONSYS_INPLACE_ENC_CONFIRM" : "OVERWRITEPROMPT_DEVICE"), type, szFileName, drive);
+			StringCbPrintfW (szTmp, sizeof(szTmp), GetString (bInPlaceEncNonSys ? (bInPlaceDecNonSys ? "NONSYS_INPLACE_DEC_CONFIRM" : "NONSYS_INPLACE_ENC_CONFIRM") : "OVERWRITEPROMPT_DEVICE"), type, szFileName, drive);
 
 
 		x = MessageBoxW (MainDlg, szTmp, lpszTitle, YES_NO | MB_ICONWARNING | (bInPlaceEncNonSys ? MB_DEFBUTTON1 : MB_DEFBUTTON2));
@@ -3339,6 +3424,15 @@ static BOOL FinalPreTransformPrompts (void)
 	return TRUE;
 }
 
+void UpdateLastDialogId (void)
+{
+	static char PageDebugId[128];
+
+	StringCbPrintfA (PageDebugId, sizeof(PageDebugId), "FORMAT_PAGE_%d", nCurPageNo);
+	LastDialogId = PageDebugId;
+}
+
+
 void HandleOldAssignedDriveLetter (void)
 {
 	if (bDevice)
@@ -3381,7 +3475,6 @@ static BOOL FileSize4GBLimitQuestionNeeded (void)
    not. - see DialogProc */
 BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
 {
-	static char PageDebugId[128];
 	WORD lw = LOWORD (wParam);
 	WORD hw = HIWORD (wParam);
 
@@ -3392,8 +3485,7 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 	case WM_INITDIALOG:
 		LocalizeDialog (hwndDlg, "IDD_VOL_CREATION_WIZARD_DLG");
 
-		StringCbPrintfA (PageDebugId, sizeof(PageDebugId), "FORMAT_PAGE_%d", nCurPageNo);
-		LastDialogId = PageDebugId;
+		UpdateLastDialogId ();
 
 		switch (nCurPageNo)
 		{
@@ -3974,7 +4066,7 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 				SetCheckBox (hwndDlg, IDC_KEYFILES_ENABLE, KeyFilesEnable);
 
-				SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString (bInPlaceEncNonSys ? "NONSYS_INPLACE_ENC_RESUME_PASSWORD_PAGE_HELP" : "PASSWORD_HIDDENVOL_HOST_DIRECT_HELP"));
+				SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString (bInPlaceEncNonSys ? (bInPlaceEncNonSysResumed ? "NONSYS_INPLACE_ENC_RESUME_PASSWORD_PAGE_HELP" : "NONSYS_INPLACE_DEC_PASSWORD_PAGE_HELP") : "PASSWORD_HIDDENVOL_HOST_DIRECT_HELP"));
 
 				SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString (bInPlaceEncNonSys ? "PASSWORD" : "PASSWORD_HIDVOL_HOST_TITLE"));
 
@@ -4367,7 +4459,7 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 			break;
 
-		case NONSYS_INPLACE_ENC_ENCRYPTION_PAGE:
+		case NONSYS_INPLACE_ENC_TRANSFORM_PAGE:
 
 			if (bInPlaceEncNonSysResumed)
 			{
@@ -4377,19 +4469,19 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 					nWipeMode = savedWipeAlgorithm;
 			}
 
-			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString ("ENCRYPTION"));
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString (bInPlaceDecNonSys ? "DECRYPTION" : "ENCRYPTION"));
 
-			SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString ("NONSYS_INPLACE_ENC_ENCRYPTION_PAGE_INFO"));
+			SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString (bInPlaceDecNonSys ? "NONSYS_INPLACE_DEC_DECRYPTION_PAGE_INFO" : "NONSYS_INPLACE_ENC_ENCRYPTION_PAGE_INFO"));
 
 			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDCANCEL), GetString (bInPlaceEncNonSysResumed ? "DEFER" : "CANCEL"));
 
 			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_PREV), GetString ("PREV"));
 
-			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), GetString (bInPlaceEncNonSysResumed ? "RESUME" : "ENCRYPT"));
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), GetString (bInPlaceEncNonSysResumed ? "RESUME" : (bInPlaceDecNonSys ? "DECRYPT" : "ENCRYPT")));
 
 			SetWindowTextW (GetDlgItem (hwndDlg, IDC_PAUSE), GetString ("IDC_PAUSE"));
 
-			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDC_PREV), !bInPlaceEncNonSysResumed);
+			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDC_PREV), !bInPlaceEncNonSysResumed && !bInPlaceDecNonSys);
 			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), TRUE);
 			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDCANCEL), TRUE);
 			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDHELP), TRUE);
@@ -4397,19 +4489,28 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 			ShowWindow (GetDlgItem (hwndDlg, IDC_MORE_INFO_SYS_ENCRYPTION), SW_HIDE);
 
-			EnableWindow (GetDlgItem (hwndDlg, IDC_WIPE_MODE), TRUE);
-			PopulateWipeModeCombo (GetDlgItem (hwndDlg, IDC_WIPE_MODE), FALSE, TRUE, FALSE);
-			SelectAlgo (GetDlgItem (hwndDlg, IDC_WIPE_MODE), (int *) &nWipeMode);
+			if (bInPlaceDecNonSys)
+			{
+				ShowWindow(GetDlgItem(hwndDlg, IDT_FORMAT_OPTIONS), SW_HIDE);
+				ShowWindow(GetDlgItem(hwndDlg, IDT_WIPE_MODE), SW_HIDE);
+				ShowWindow(GetDlgItem(hwndDlg, IDC_WIPE_MODE), SW_HIDE);
+			}
+			else
+			{
+				EnableWindow (GetDlgItem (hwndDlg, IDC_WIPE_MODE), TRUE);
+				PopulateWipeModeCombo (GetDlgItem (hwndDlg, IDC_WIPE_MODE), FALSE, TRUE, FALSE);
+				SelectAlgo (GetDlgItem (hwndDlg, IDC_WIPE_MODE), (int *) &nWipeMode);
+			}
 
 			break;
 
-		case NONSYS_INPLACE_ENC_ENCRYPTION_FINISHED_PAGE:
+		case NONSYS_INPLACE_ENC_TRANSFORM_FINISHED_PAGE:
 
 			bConfirmQuit = FALSE;
 
-			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString ("NONSYS_INPLACE_ENC_FINISHED_TITLE"));
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString (bInPlaceDecNonSys ? "NONSYS_INPLACE_DEC_FINISHED_TITLE" : "NONSYS_INPLACE_ENC_FINISHED_TITLE"));
 
-			SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString ("NONSYS_INPLACE_ENC_FINISHED_INFO"));
+			SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString (bInPlaceDecNonSys ? "NONSYS_INPLACE_DEC_FINISHED_INFO" : "NONSYS_INPLACE_ENC_FINISHED_INFO"));
 
 			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_PREV), GetString ("PREV"));
 			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), GetString ("FINALIZE"));
@@ -4421,6 +4522,54 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 			break;
 
+		case NONSYS_INPLACE_DEC_TRANSFORM_FINISHED_DRIVE_LETTER_PAGE:
+
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_BOX_TITLE), GetString ("NONSYS_INPLACE_DEC_FINISHED_TITLE"));
+
+			SetWindowTextW (GetDlgItem (hwndDlg, IDC_BOX_HELP), GetString ("NONSYS_INPLACE_DEC_FINISHED_DRIVE_LETTER_SEL_INFO"));
+
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_PREV), GetString ("PREV"));
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), GetString ("FINALIZE"));
+			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDC_PREV), FALSE);
+			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDC_NEXT), TRUE);
+
+			SetWindowTextW (GetDlgItem (GetParent (hwndDlg), IDCANCEL), GetString ("CANCEL"));
+
+			// The Cancel button and the X button must be disabled to prevent the user from forgetting to assign a drive letter to the partition by closing 
+			// the window accidentally or clicking Cancel. The user is forced to click Finish to assign at least the pre-selected free drive letter.
+			// This is critical because inexperienced users would not know how to access data on the decrypted volume without a drive letter.
+			EnableWindow (GetDlgItem (GetParent (hwndDlg), IDCANCEL), FALSE);
+			DisableCloseButton (MainDlg);
+			bConfirmQuit = TRUE;	// Alt-F4 will still work but the user will be prompted to confirm the action.
+
+			// Decryption of non-system volume finished, no drive letter is assigned to the decrypted volume, and free drive letters are available. 
+			// This is critical because inexperienced users would not know how to access data on the decrypted volume. We cannot allow exit
+			// until a drive letter is freed up and assigned to the decrypted volume.
+
+			while (GetFirstAvailableDrive () == -1)
+			{
+				Error ("NONSYS_INPLACE_DEC_FINISHED_NO_DRIVE_LETTER_AVAILABLE", hwndDlg);
+			}
+
+			// Populate the combobox with free drive letters
+			{
+				DWORD dwUsedDrives = GetLogicalDrives();
+				char szDriveLetter[] = {' ', ':', 0 };
+				int i;
+
+				for (i = 0; i < 26; i++)
+				{
+					if (!(dwUsedDrives & 1 << i))
+					{
+						// Add
+						szDriveLetter [0] = (char) (i + 'A');
+						AddComboPair (GetDlgItem (hCurPage, IDC_DRIVE_LETTER_LIST), szDriveLetter, i);
+					}
+				}
+			}
+			SendMessage (GetDlgItem (hwndDlg, IDC_DRIVE_LETTER_LIST), CB_SETCURSEL, 0, 0);
+			break;
+
 		case FORMAT_PAGE:
 			{
 				BOOL bNTFSallowed = FALSE;
@@ -4967,7 +5116,7 @@ BOOL CALLBACK PageDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 				}
 				break;
 
-			case  NONSYS_INPLACE_ENC_ENCRYPTION_PAGE:
+			case  NONSYS_INPLACE_ENC_TRANSFORM_PAGE:
 				{
 					switch (lw)
 					{
@@ -5664,6 +5813,8 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 						KillTimer (hwndDlg, TIMER_ID_SYSENC_PROGRESS);
 
+						UpdateLastDialogId ();
+
 						try
 						{
 							if (BootEncStatus.DriveMounted)	// If we had been really encrypting/decrypting (not just proceeding to deinstall)
@@ -5788,6 +5939,8 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 				if (!bVolTransformThreadRunning && !bVolTransformThreadToRun)
 				{
 					KillTimer (hwndDlg, TIMER_ID_NONSYS_INPLACE_ENC_PROGRESS);
+
+					UpdateLastDialogId ();
 				}
 
 				UpdateNonSysInPlaceEncControls ();
@@ -5927,6 +6080,7 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 						// The driver stopped wiping
 
 						KillTimer (hwndDlg, TIMER_ID_WIPE_PROGRESS);
+						UpdateLastDialogId ();
 
 						try
 						{
@@ -6010,8 +6164,29 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 		KillTimer (hwndDlg, TIMER_ID_NONSYS_INPLACE_ENC_PROGRESS);
 
-		LoadPage (hwndDlg, NONSYS_INPLACE_ENC_ENCRYPTION_FINISHED_PAGE);
+		if (bInPlaceDecNonSys)
+		{
+			// Decryption of non-system volume finished and free drive letters are available. Check if a drive letter is assigned to the decrypted volume.
+
+			WCHAR deviceName[MAX_PATH + 1];
 
+			StringCbCopyA ((char *)deviceName, sizeof(deviceName), szDiskFile);
+			ToUNICODE ((char *)deviceName, sizeof(deviceName));
+
+			if (GetDiskDeviceDriveLetter (deviceName) < 0)		
+			{
+				// No drive letter is assigned to the device
+				MessageBeep (MB_OK);
+				LoadPage (hwndDlg, NONSYS_INPLACE_DEC_TRANSFORM_FINISHED_DRIVE_LETTER_PAGE);
+				return 1;
+			}
+			else
+			{
+				Info ("NONSYS_INPLACE_DEC_FINISHED_INFO", hwndDlg);
+			}
+		}
+
+		LoadPage (hwndDlg, NONSYS_INPLACE_ENC_TRANSFORM_FINISHED_PAGE);
 		return 1;
 
 	case TC_APPMSG_VOL_TRANSFORM_THREAD_ENDED:
@@ -6050,7 +6225,7 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 
 	case TC_APPMSG_FORMAT_USER_QUIT:
 
-		if (nCurPageNo == NONSYS_INPLACE_ENC_ENCRYPTION_PAGE
+		if (nCurPageNo == NONSYS_INPLACE_ENC_TRANSFORM_PAGE
 			&& (bVolTransformThreadRunning || bVolTransformThreadToRun || bInPlaceEncNonSysResumed))
 		{
 			// Non-system encryption in progress
@@ -6970,10 +7145,10 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 						}
 					}
 				}
-				else
+				else if (bInPlaceEncNonSysResumed)
 				{
 					/* Scan all available partitions to discover all partitions where non-system in-place
-					encryption has been interrupted. */
+					encryption/decryption has been interrupted. */
 
 					BOOL tmpbDevice;					
 
@@ -7002,12 +7177,115 @@ BOOL CALLBACK MainDialogProc (HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lPa
 							return 1;
 						}
 
-						nNewPageNo = NONSYS_INPLACE_ENC_ENCRYPTION_PAGE - 1;	// Skip irrelevant pages
+						nNewPageNo = NONSYS_INPLACE_ENC_TRANSFORM_PAGE - 1;	// Skip irrelevant pages
 					}
 
 					NormalCursor();
 				}
+				else
+				{
+					/* Try to mount the non-system volume to decrypt in place (the process has not started yet, we are NOT trying to resume it). 
+					   We will try to mount it using the backup header, which we require to work (i.e. be non-damaged) before we start writing
+					   to the volume (the primary header will be overwritten by decrypted data soon after the decryption process begins, so the 
+					   backup header will contain the only copy of the master key). */
+
+					int driveNo = -1;
+
+					// The volume may already be mounted. We need to dismount it first in order to verify the supplied password/keyfile(s) is/are correct. 
+					if (IsMountedVolume (szFileName))
+					{
+						driveNo = GetMountedVolumeDriveNo (szFileName);
+
+						if (driveNo == -1
+							|| !UnmountVolume (hwndDlg, driveNo, TRUE))
+						{
+							handleWin32Error (MainDlg);
+							AbortProcess ("CANT_DISMOUNT_VOLUME");
+						}
+					}
+
+					driveNo = GetLastAvailableDrive ();
+
+					if (driveNo < 0)
+						AbortProcess ("NO_FREE_DRIVES");
+
+					MountOptions mountOptions;
+					ZeroMemory (&mountOptions, sizeof (mountOptions));
+
+					mountOptions.UseBackupHeader = FALSE;	// This must be FALSE at this point because otherwise we wouldn't be able to detect a legacy volume
+					mountOptions.ReadOnly = TRUE;
+					mountOptions.Removable = ConfigReadInt ("MountVolumesRemovable", FALSE);
+
+					// Check that it is not a hidden or legacy volume
+
+					if (MountVolume (hwndDlg, driveNo, szFileName, &volumePassword, hash_algo, FALSE, FALSE, TRUE, &mountOptions, FALSE, TRUE) < 1)
+					{
+						NormalCursor();
+						return 1;
+					}
+
+					{
+						DWORD dwResult;
+						VOLUME_PROPERTIES_STRUCT volProp;
+
+						memset (&volProp, 0, sizeof(volProp));
+						volProp.driveNo = driveNo;
+						if (!DeviceIoControl (hDriver, TC_IOCTL_GET_VOLUME_PROPERTIES, &volProp, sizeof (volProp), &volProp, sizeof (volProp), &dwResult, NULL) || dwResult == 0)
+						{
+							handleWin32Error (hwndDlg);
+							UnmountVolume (hwndDlg, driveNo, TRUE);
+							AbortProcess ("CANT_GET_VOL_INFO");
+						}
+
+						if (volProp.volFormatVersion == TC_VOLUME_FORMAT_VERSION_PRE_6_0)
+						{
+							UnmountVolume (hwndDlg, driveNo, TRUE);
+							AbortProcess ("NONSYS_INPLACE_DECRYPTION_BAD_VOL_FORMAT");
+						}
+
+						if (volProp.hiddenVolume)
+						{
+							UnmountVolume (hwndDlg, driveNo, TRUE);
+							AbortProcess ("NONSYS_INPLACE_DECRYPTION_CANT_DECRYPT_HID_VOL");
+						}
+					}
+
+					// Remount the volume using the backup header to verify it is working
+
+					if (!UnmountVolume (hwndDlg, driveNo, TRUE))
+					{
+						handleWin32Error (MainDlg);
+						AbortProcess ("CANT_DISMOUNT_VOLUME");
+					}
+
+					mountOptions.UseBackupHeader = TRUE;	// This must be TRUE at this point (we won't be using the regular header, which will be lost soon after the decryption process starts)
+
+					if (MountVolume (hwndDlg, driveNo, szFileName, &volumePassword, hash_algo, FALSE, FALSE, TRUE, &mountOptions, FALSE, TRUE) < 1)
+					{
+						NormalCursor();
+						return 1;
+					}
+
+					if (!UnmountVolume (hwndDlg, driveNo, TRUE))
+					{
+						handleWin32Error (MainDlg);
+						AbortProcess ("CANT_DISMOUNT_VOLUME");
+					}
+
+					BOOL tmpbDevice;
+
+					CreateFullVolumePath (szDiskFile, sizeof(szDiskFile), szFileName, &tmpbDevice);
+
+					nVolumeSize = GetDeviceSize (szDiskFile);
+					if (nVolumeSize == -1)
+					{
+						handleWin32Error (MainDlg);
+						AbortProcessSilent ();
+					}
 
+					nNewPageNo = NONSYS_INPLACE_ENC_TRANSFORM_PAGE - 1;	// Skip irrelevant pages
+					NormalCursor();
+				}
 			}
 
 			else if (nCurPageNo == FILESYS_PAGE)
@@ -7312,20 +7590,76 @@ retryCDDriveCheck:
 			}
 			else if (nCurPageNo == NONSYS_INPLACE_ENC_RESUME_PARTITION_SEL_PAGE)
 			{
-				nNewPageNo = NONSYS_INPLACE_ENC_ENCRYPTION_PAGE - 1;	// Skip irrelevant pages
+				nNewPageNo = NONSYS_INPLACE_ENC_TRANSFORM_PAGE - 1;	// Skip irrelevant pages
 			}
-			else if (nCurPageNo == NONSYS_INPLACE_ENC_ENCRYPTION_PAGE)
+			else if (nCurPageNo == NONSYS_INPLACE_ENC_TRANSFORM_PAGE)
 			{
 				/* In-place encryption start  (the 'Next' button has been clicked) */
+				if (bInPlaceDecNonSys
+					&& !bInPlaceEncNonSysResumed
+					&& AskWarnYesNo ("NONSYS_INPLACE_ENC_CONFIRM_BACKUP", hwndDlg) == IDNO)
+				{
+					// Cancel
+					return 1;
+				}
 
 				NonSysInplaceEncResume ();
 				return 1;
 			}
-			else if (nCurPageNo == NONSYS_INPLACE_ENC_ENCRYPTION_FINISHED_PAGE)
+			else if (nCurPageNo == NONSYS_INPLACE_ENC_TRANSFORM_FINISHED_PAGE)
 			{
 				PostMessage (hwndDlg, TC_APPMSG_FORMAT_USER_QUIT, 0, 0);
 				return 1;
 			}
+			else if (nCurPageNo == NONSYS_INPLACE_DEC_TRANSFORM_FINISHED_DRIVE_LETTER_PAGE)
+			{
+				BOOL bDrvLetterAssignResult = FALSE;
+
+				int tmpDriveLetter = (int) SendMessage (GetDlgItem (hCurPage, IDC_DRIVE_LETTER_LIST),
+						CB_GETITEMDATA, 
+						SendMessage (GetDlgItem (hCurPage, IDC_DRIVE_LETTER_LIST), CB_GETCURSEL, 0, 0),
+						0);
+
+				if (tmpDriveLetter < 0)
+					tmpDriveLetter = GetFirstAvailableDrive ();
+
+				do
+				{
+					char szDriveLetter[] = {'A', ':', 0 };
+					char rootPath[] = {'A', ':', '\\', 0 };
+					char uniqVolName[MAX_PATH+1] = { 0 };
+
+					rootPath[0] += (char) tmpDriveLetter;
+					szDriveLetter[0] += (char) tmpDriveLetter;
+
+					if (DefineDosDevice (DDD_RAW_TARGET_PATH, szDriveLetter, szDiskFile))
+					{
+						bDrvLetterAssignResult = GetVolumeNameForVolumeMountPoint (rootPath, uniqVolName, MAX_PATH);
+
+						DefineDosDevice (DDD_RAW_TARGET_PATH|DDD_REMOVE_DEFINITION|DDD_EXACT_MATCH_ON_REMOVE,
+							szDriveLetter,
+							szDiskFile);
+
+						if (bDrvLetterAssignResult) 
+						{
+							if (SetVolumeMountPoint (rootPath, uniqVolName) == 0)
+								bDrvLetterAssignResult = FALSE;
+						}
+					}
+
+					if (!bDrvLetterAssignResult)
+					{
+						if (AskErrYesNo ("ERR_CANNOT_ASSIGN_DRIVE_LETTER_NONSYS_DEC", hwndDlg) == IDNO)
+							break;
+					}
+
+				} while (bDrvLetterAssignResult == FALSE);
+
+				bConfirmQuit = FALSE;
+
+				PostMessage (hwndDlg, TC_APPMSG_FORMAT_USER_QUIT, 0, 0);
+				return 1;
+			}
 			else if (nCurPageNo == FORMAT_PAGE)
 			{
 				/* Format start  (the 'Next' button has been clicked on the Format page) */
@@ -7906,26 +8240,33 @@ void ExtractCommandLine (HWND hwndDlg, char *lpszCommandLine)
 				CommandDecryptSysEnc,
 				CommandEncDev,
 				CommandHiddenSys,
-				CommandResumeInplaceLogOn,
+				CommandResumeNonSysInplaceLogOn,
 				CommandResumeHiddenSys,
 				CommandSysEnc,
+				CommandInplaceDec,
+				CommandResumeInplaceDec,
 				CommandResumeInplace,
 			};
 
 			argument args[]=
 			{
+				// Public
 				{ OptionHistory,				"/history",			"/h", FALSE },
 				{ OptionNoIsoCheck,				"/noisocheck",		"/n", FALSE },
 				{ OptionTokenLib,				"/tokenlib",		NULL, FALSE },
 				{ OptionQuit,					"/quit",			"/q", FALSE },
+
+				// Internal 
 				{ CommandResumeSysEncLogOn,		"/acsysenc",		"/a", TRUE },
 				{ CommandResumeSysEnc,			"/csysenc",			"/c", TRUE },
 				{ CommandDecryptSysEnc,			"/dsysenc",			"/d", TRUE },
 				{ CommandEncDev,				"/encdev",			"/e", TRUE },
 				{ CommandHiddenSys,				"/isysenc",			"/i", TRUE },	
-				{ CommandResumeInplaceLogOn,	"/prinplace",		"/p", TRUE },
+				{ CommandResumeNonSysInplaceLogOn,	"/prinplace",		"/p", TRUE },
 				{ CommandResumeHiddenSys,		"/risysenc",		"/r", TRUE },	
 				{ CommandSysEnc,				"/sysenc",			"/s", TRUE },	
+				{ CommandInplaceDec,				"/inplacedec",		NULL, TRUE },
+				{ CommandResumeInplaceDec,			"/resumeinplacedec",NULL, TRUE },
 				{ CommandResumeInplace,			"/zinplace",		"/z", TRUE }
 			};
 
@@ -8053,12 +8394,36 @@ void ExtractCommandLine (HWND hwndDlg, char *lpszCommandLine)
 				DirectDeviceEncMode = TRUE;
 				break;
 
+			case CommandInplaceDec:
+				// Start (not resume) decrypting the specified non-system volume in place
+				{
+					char szTmp [TC_MAX_PATH + 8000] = {0};
+
+					GetArgumentValue (lpszCommandLineArgs, &i, nNoCommandLineArgs, szTmp, sizeof (szTmp));
+
+					if (strlen (szTmp) < 1)
+					{
+						// No valid volume path specified as command-line parameter
+						AbortProcess ("ERR_PARAMETER_INCORRECT");
+					}
+
+					memset (szFileName, 0, sizeof (szFileName));
+					StringCbCopyA (szFileName, sizeof (szFileName), szTmp);
+					DirectNonSysInplaceDecStartMode = TRUE;
+				}
+				break;
+
 			case CommandResumeInplace:
 				// Resume interrupted process of non-system in-place encryption of a partition
 				DirectNonSysInplaceEncResumeMode = TRUE;
 				break;
 
-			case CommandResumeInplaceLogOn:
+			case CommandResumeInplaceDec:
+				// Resume interrupted process of non-system in-place decryption of a partition
+				DirectNonSysInplaceDecResumeMode = TRUE;
+				break;
+
+			case CommandResumeNonSysInplaceLogOn:
 				// Ask the user whether to resume interrupted process of non-system in-place encryption of a partition
 				// This switch is passed only by the system (from the startup sequence).
 				DirectPromptNonSysInplaceEncResumeMode = TRUE;
@@ -8641,7 +9006,7 @@ static void AfterWMInitTasks (HWND hwndDlg)
 			else
 			{
 				// Nothing to resume
-				Warning ("NOTHING_TO_RESUME", hwndDlg);
+				Warning ("NO_SYS_ENC_PROCESS_TO_RESUME", hwndDlg);
 				EndMainDlg (MainDlg);
 
 				return;
@@ -8985,7 +9350,7 @@ static void AfterWMInitTasks (HWND hwndDlg)
 			&& !bInPlaceEncNonSysPending)
 		{
 			// This instance of the wizard has been launched via the system startup sequence to prompt for resume of
-			// a non-system in-place encryption process. However, no config file indicates that any such process
+			// a non-system in-place encryption/decryption process. However, no config file indicates that any such process
 			// has been interrupted. This inconsistency may occur, for example, when the process is finished
 			// but the wizard is not removed from the startup sequence because system encryption is in progress.
 			// Therefore, we remove it from the startup sequence now if possible.
@@ -8996,9 +9361,16 @@ static void AfterWMInitTasks (HWND hwndDlg)
 			AbortProcessSilent ();
 		}
 
-		if (DirectNonSysInplaceEncResumeMode)
+		BOOL bDecrypt = FALSE;
+
+		if (DirectNonSysInplaceDecStartMode)
+		{
+			SwitchWizardToNonSysInplaceDecStartMode (szFileName);
+			return;
+		}
+		else if (DirectNonSysInplaceEncResumeMode || DirectNonSysInplaceDecResumeMode)
 		{
-			SwitchWizardToNonSysInplaceEncResumeMode();
+			SwitchWizardToNonSysInplaceEncResumeMode (DirectNonSysInplaceDecResumeMode);
 			return;
 		}
 		else if (DirectPromptNonSysInplaceEncResumeMode)
@@ -9006,8 +9378,8 @@ static void AfterWMInitTasks (HWND hwndDlg)
 			if (NonSysInplaceEncInProgressElsewhere ())
 				AbortProcessSilent ();
 
-			if (AskNonSysInPlaceEncryptionResume(hwndDlg) == IDYES)
-				SwitchWizardToNonSysInplaceEncResumeMode();
+			if (AskNonSysInPlaceEncryptionResume(hwndDlg, &bDecrypt) == IDYES)
+				SwitchWizardToNonSysInplaceEncResumeMode(bDecrypt);
 			else
 				AbortProcessSilent ();
 
@@ -9015,9 +9387,9 @@ static void AfterWMInitTasks (HWND hwndDlg)
 		}
 		else if (bInPlaceEncNonSysPending
 			&& !NonSysInplaceEncInProgressElsewhere ()
-			&& AskNonSysInPlaceEncryptionResume(hwndDlg) == IDYES)
+			&& AskNonSysInPlaceEncryptionResume(hwndDlg, &bDecrypt) == IDYES)
 		{
-			SwitchWizardToNonSysInplaceEncResumeMode();
+			SwitchWizardToNonSysInplaceEncResumeMode(bDecrypt);
 			return;
 		}
 
diff --git a/src/Format/Tcformat.h b/src/Format/Tcformat.h
index 77579f54..15a81534 100644
--- a/src/Format/Tcformat.h
+++ b/src/Format/Tcformat.h
@@ -42,6 +42,7 @@ void DisplaySizingErrorText ( HWND hwndTextBox );
 void EnableDisableFileNext ( HWND hComboBox , HWND hMainButton );
 BOOL QueryFreeSpace ( HWND hwndDlg , HWND hwndTextBox , BOOL display );
 static BOOL FinalPreTransformPrompts (void);
+void UpdateLastDialogId (void);
 void HandleOldAssignedDriveLetter (void);
 void AddCipher ( HWND hComboBox , char *lpszCipher , int nCipher );
 BOOL CALLBACK PageDialogProc ( HWND hwndDlg , UINT uMsg , WPARAM wParam , LPARAM lParam );
@@ -90,6 +91,7 @@ extern volatile BOOL bVolTransformThreadCancel;
 extern volatile BOOL bInPlaceEncNonSysResumed;
 extern volatile BOOL bFirstNonSysInPlaceEncResumeDone;
 extern volatile BOOL bInPlaceEncNonSys;
+extern volatile BOOL bInPlaceDecNonSys;
 extern __int64 NonSysInplaceEncBytesDone;
 extern __int64 NonSysInplaceEncTotalSize;
 extern int nPbar;