VBoxManage encryptmedium - cipher validation and documentation

[andy-g]

Hi, As reported in ​https://forums.virtualbox.org/viewtopic.php?f=6&t=87254, i had some issues encrypting a disk.

Long story short, the encryptmedium command requires a cipher parameter, but a) does not validate it is present and b) does not present clear usage instructions (in my humble opinion).

Can I suggest that a check is done in handleEncryptMedium (VBoxManageDisk.cpp, line 1756) that if a user has provided a new password and password id, but no old password, that either the method picks a cipher by default if none is provided or reports the issue to the user. At the moment the error reported is pretty misleading.

For example:

VBoxManage encryptmedium 2f6ab46f-8db4-44d9-af1e-152c35178724 --newpasswordid test --newpassword -
Enter new password:
0%...
Progress state: VBOX_E_INVALID_OBJECT_STATE
VBoxManage.exe: error: Failed to encrypt hard disk
VBoxManage.exe: error: The password and password identifier must be empty if the output should be unencrypted
VBoxManage.exe: error: Details: code VBOX_E_INVALID_OBJECT_STATE (0x80bb0007), component MediumWrap, interface IMedium
VBoxManage.exe: error: Context: "enum RTEXITCODE __cdecl handleEncryptMedium(struct HandlerArg *)" at line 1890 of file VBoxManageDisk.cpp

Supplying the cipher:

VBoxManage encryptmedium 2f6ab46f-8db4-44d9-af1e-152c35178724 --newpasswordid test --newpassword - --cipher AES-XTS128-PLAIN64
Enter new password:
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%