I want to detect the device encryption support in my program. This info is available in the System Information program. Please check out the screenshot below:
What kind of Win API functions are used/available to detect the device encryption support? What System Information program uses to detect it? I just need some information.
TL;DR: it uses undocumented functions from fveapi.dll (Windows Bitlocker Drive Encryption API). It seems to rely only on the TPM capabilities.
Note that I only spent like 15 mins on it, but I doubt I missed something crucial, althoug this might be possible.
Typed system information in search bar, saw it spawned msinfo32.exe. Put the binary in a disassembler. It uses a MUI file so I'll have to search for the strings in the MUI file and not the executable.
Searching Device Encryption Support leads to string ID 951 (0x3b7)
STRINGTABLE
LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US
{
951, "Device Encryption Support|%s"
Searching for the contant in the disassembler leads to a function named:
DeviceEncryptionDataPoints(struct CWMIHelper *, struct CPtrList *)
The load ing of the aforementioned string is almost right at the start:
.text:00000001400141E9 mov edx, 3B7h
.text:00000001400141EE lea rcx, [rsp+2C8h+var_280]
.text:00000001400141F3
.text:00000001400141F3 loc_1400141F3:
.text:00000001400141F3 ; try {
.text:00000001400141F3 call cs:__imp_?LoadStringW@CString@@QEAAHI@Z ; CString::LoadStringW(uint)
So we are definitely in the right function.
It loads the fveapi.dll module:
.text:0000000140014269 xor edx, edx ; hFile
.text:000000014001426B mov r8d, 800h ; dwFlags
.text:0000000140014271 lea rcx, LibFileName ; "fveapi.dll"
.text:0000000140014278 call cs:__imp_LoadLibraryExW
Gets a pointer on FveQueryDeviceEncryptionSupport:
.text:00000001400142AB lea rdx, aFvequerydevice ; "FveQueryDeviceEncryptionSupport"
.text:00000001400142B2 mov rcx, rdi ; hModule
.text:00000001400142B5 call cs:__imp_GetProcAddress
And immediately calls the function (this is a protected CFG call, but it's here):
.text:00000001400142CA mov [rsp+2C8h+var_254], rbx
.text:00000001400142CF mov [rsp+2C8h+var_260], 14h
.text:00000001400142D7 mov [rsp+2C8h+var_25C], 1
.text:00000001400142DF mov [rsp+2C8h+var_258], 1
.text:00000001400142E7 lea rcx, [rsp+2C8h+var_260]
.text:00000001400142EC call cs:__guard_dispatch_icall_fptr
If the function fails:
.text:00000001400142EC call cs:__guard_dispatch_icall_fptr
.text:00000001400142F2 mov esi, eax
.text:00000001400142F4 test eax, eax
.text:00000001400142F6 js loc_1400143F0 ; check failure
We land here:
.text:00000001400143F7 mov edx, 2FFh
.text:00000001400143FC lea rcx, [rsp+2C8h+var_288]
.text:0000000140014401 call cs:__imp_?LoadStringW@CString@@QEAAHI@Z ; CString::LoadStringW(uint)
The string 0x2FF (767) is:
767, "Elevation Required to View"
If the call succeed, the code checks one of the parameter which is definitly an out parameter:
.text:00000001400142EC call cs:__guard_dispatch_icall_fptr
.text:00000001400142F2 mov esi, eax
.text:00000001400142F4 test eax, eax
.text:00000001400142F6 js loc_1400143F0
.text:00000001400142FC cmp dword ptr [rsp+2C8h+var_254], ebx ; rbx = 0
.text:0000000140014300 jnz short loc_14001431D
.text:0000000140014302 mov edx, 3B8h
.text:0000000140014307 lea rcx, [rsp+2C8h+var_288]
.text:000000014001430C call cs:__imp_?LoadStringW@CString@@QEAAHI@Z ; CString::LoadStringW(uint)
If it's 0, the string 0x3b8 (952) is used:
952, "Meets prerequisites"
Otherwise various failure functions are called.
In case of a failure, the UpdateDeviceEncryptionStateFailureString function is called:
.text:0000000140014325 lea r9, [rsp+2C8h+var_294] ; int *
.text:000000014001432A lea r8, [rsp+2C8h+var_290] ; int *
.text:000000014001432F mov edx, 3C1h ; unsigned int
.text:0000000140014334 lea rcx, [rsp+2C8h+var_288] ; struct CString *
.text:0000000140014339 call ?UpdateDeviceEncryptionStateFailureString@@YAXPEAVCString@@IPEAH1@Z ; UpdateDeviceEncryptionStateFailureString(CString *,uint,int *,int *)
Its main goal is to fetch some string from the resource file.
One that stands out is 0x3b9:
.text:0000000140013A37 mov edx, 3B9h
.text:0000000140013A3C mov rcx, rbx
.text:0000000140013A3F call cs:__imp_?LoadStringW@CString@@QEAAHI@Z ; CString::LoadStringW(uint)
953, "Reasons for failed automatic device encryption"
Which is the case for me since I don't have a TPM.
All of the other functions called from the DeviceEncryptionDataPoints (at least to get the needed results) are all from the fveapi.dll.
There are a lot in a function called PerformIndividualHardwareTests(HINSTANCE hModule, struct CString *, int *, int *):
.text:0000000140013AEF lea rdx, aNgscbcheckisao ; "NgscbCheckIsAOACDevice"
.text:0000000140013AF6 mov [rbp+var_1F], 0
.text:0000000140013AFA mov rdi, r9
.text:0000000140013AFD mov [rbp+var_20], 0
.text:0000000140013B01 mov rsi, r8
.text:0000000140013B04 mov [rbp+var_1E], 0
.text:0000000140013B08 mov rbx, rcx
.text:0000000140013B0B call cs:__imp_GetProcAddress
.text:0000000140013B12 nop dword ptr [rax+rax+00h]
.text:0000000140013B17 mov r12, rax
.text:0000000140013B1A test rax, rax
.text:0000000140013B1D jz loc_140013CB9
.text:0000000140013B23 lea rdx, aNgscbcheckishs ; "NgscbCheckIsHSTIVerified"
.text:0000000140013B2A mov rcx, rbx ; hModule
.text:0000000140013B2D call cs:__imp_GetProcAddress
.text:0000000140013B34 nop dword ptr [rax+rax+00h]
.text:0000000140013B39 mov r15, rax
.text:0000000140013B3C test rax, rax
.text:0000000140013B3F jz loc_140013CB9
.text:0000000140013B45 lea rdx, aNgscbcheckhsti ; "NgscbCheckHSTIPrerequisitesVerified"
.text:0000000140013B4C mov rcx, rbx ; hModule
.text:0000000140013B4F call cs:__imp_GetProcAddress
.text:0000000140013B56 nop dword ptr [rax+rax+00h]
.text:0000000140013B5B mov r13, rax
.text:0000000140013B5E test rax, rax
.text:0000000140013B61 jz loc_140013CB9
.text:0000000140013B67 lea rdx, aNgscbcheckdmas ; "NgscbCheckDmaSecurity"
.text:0000000140013B6E mov rcx, rbx ; hModule
.text:0000000140013B71 call cs:__imp_GetProcAddress
There's also a registry key checked SYSTEM\CurrentControlSet\Control\BitLocker\AutoDE\HSTI:
.text:0000000140013C10 lea r8, ?NGSCB_AUTODE_HSTI_REQUIRED@@3QBGB ; "HSTIVerificationRequired"
.text:0000000140013C17 mov [rsp+60h+pcbData], rax ; pcbData
.text:0000000140013C1C lea rdx, ?NGSCB_AUTODE_HSTI_PREREQS@@3QBGB ; "SYSTEM\\CurrentControlSet\\Control\\Bit"...
.text:0000000140013C23 lea rax, [rbp+var_1C]
.text:0000000140013C27 mov r9d, 10h ; dwFlags
.text:0000000140013C2D mov [rsp+60h+pvData], rax ; pvData
.text:0000000140013C32 mov rcx, 0FFFFFFFF80000002h ; hkey
.text:0000000140013C39 and [rsp+60h+var_40], 0
.text:0000000140013C3F call cs:__imp_RegGetValueW
and some other functions (NgscbCheckPreventDeviceEncryption, NgscbGetWinReConfiguration, FveCheckTpmCapability, ...) , once again, all from the fveapi.dll module.
So basically the checks are all based on functions from this DLL. It seems that none of them are documented (as far as I can see with a quick search).
I didn't find anything around in the DeviceEncryptionDataPoints caller (which is basically the main() function), since the next calls are dealing with checking the hypervisor capabilities.