If you have to go the private file route, this may help. It creates a file that can only be read by the current userid, and writes the password to it. It then waits for keyboard input and deletes the file.

I've verified that other users, including administrators cannot read or delete the file, nor even inspect its permissions.

Also, in theory, by using FILE_ATTRIBUTE_TEMPORARY, the contents may never actually be written to the disk, and (assuming a small file and a system file cache that is not overrun) only ever exist in cache. (In theory!)

#include <windows.h>
#include <sddl.h>
#include <stdio.h>
#include <conio.h>
#include <Lmcons.h>
#include "debug.h"

#define TESTFILENAME "PermissionsTest.txt"

int main( int argc, char **argv ) {
    char userName[ UNLEN+1 ];
    char sid[ 400 ];
    char *stringSID;
    char domainName[ 256 ];
    SID_NAME_USE sidType;
    char pswd[] = "The quick brown fox";
    char ssdTemplate[] = "O:%sD:P(A;;FA;;;%s)";
    char ssd[1024];
    SECURITY_DESCRIPTOR *psd = NULL;
    SECURITY_ATTRIBUTES sa = { sizeof( SECURITY_ATTRIBUTES ), NULL, 0 
+};
    ULONG sdSize, unSize = sizeof( userName ), sidSize = sizeof( sid )
+, dnSize = sizeof( domainName ), written;
    HANDLE h;


    DIEIF( !GetUserName( userName, &unSize ), NULL );
    DIEIF( !LookupAccountName( NULL, userName, sid, &sidSize, domainNa
+me, &dnSize, &sidType ), NULL );
    printf( "Got sid\n" );
    DIEIF( !ConvertSidToStringSid( sid, &stringSID ), NULL );
    printf( "SID (as string): '%s'\n", stringSID );

    sprintf_s( ssd, sizeof(ssd), ssdTemplate, stringSID, stringSID );
    printf( "SSD: '%s'\n", ssd );

    DIEIF( !ConvertStringSecurityDescriptorToSecurityDescriptor( ssd, 
+SDDL_REVISION_1, &psd, &sdSize ), NULL );
    printf( "psd:%x sdSize: %d\n", psd, sdSize );
    sa.lpSecurityDescriptor =  psd;
    DIEIF( ( h = CreateFile(
            TESTFILENAME, GENERIC_WRITE, FILE_SHARE_READ, &sa, CREATE_
+ALWAYS,
            FILE_ATTRIBUTE_TEMPORARY, NULL
        )) == INVALID_HANDLE_VALUE, NULL
    );
    printf("File created\n" );
    DIEIF( !WriteFile( h, pswd, sizeof( pswd ), &written, NULL ), NULL
+ );
    printf( "File written '%s'\n", pswd );

    while( !_kbhit() ) Sleep( 1 );

    printf( "Closing file\n" );
    DIEIF( !CloseHandle( h ), NULL );
    DIEIF( !DeleteFile( TESTFILENAME ), NULL );
    return 0;
}
[download]

I am currently trying to make a module from that: https://github.com/salva/p5-Win32-SecretFile

When I tried to build Win32::SecretFile I got the following errors:

C:\perl64\packages\p5-Win32-SecretFile-master>nmake

Microsoft (R) Program Maintenance Utility Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

        C:\Perl64\bin\perl.exe C:\perl64\site\lib\ExtUtils\xsubpp  -ty
+pemap C:\Perl64\lib\ExtUtils\typemap  SecretFile.xs > SecretFile.xsc 
+&& C:\Perl64\bin\perl.exe -MExtUtils::Command -e mv -- SecretFile.xsc
+ SecretFile.c
Please specify prototyping behavior for SecretFile.xs (see perlxs manu
+al)
        cl -c  -I.  -nologo -GF -W3 -MD -Zi -Ox -GL -fp:precise -DWIN3
+2 -D_CONSOLE -DNO_STRICT -DHAVE_DES_FCRYPT -DWIN64 -DUSE_SITECUSTOMIZ
+E -DPRIVLIB_LAST_IN_INC -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -
+DUSE_PERLIO -DPERL_MSVCRT_READFIX -MD -Zi -Ox -GL -fp:precise    -DVE
+RSION=\"0.01\"  -DXS_VERSION=\"0.01\"  "-IC:\Perl64\lib\CORE"   Secre
+tFile.c
SecretFile.c
SecretFile.xs(55) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(58) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(58) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(82) : warning C4013: 'ConvertSidToStringSid' undefined; 
+assuming extern returning int
SecretFile.xs(87) : warning C4013: 'ConvertStringSecurityDescriptorToS
+ecurityDescriptor' undefined; assuming extern returning int
SecretFile.xs(99) : warning C4267: 'function' : conversion from 'size_
+t' to 'DWORD', possible loss of data
        link -out:blib\arch\auto\Win32\SecretFile\SecretFile.dll -dll 
+-nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -libpath:"C:\Perl64\
+lib\CORE"  -machine:AMD64 SecretFile.obj   C:\Perl64\lib\CORE\perl510
+.lib oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  com
+dlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.l
+ib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbc
+cp32.lib comctl32.lib bufferoverflowU.lib msvcrt.lib -def:SecretFile.
+def
   Creating library blib\arch\auto\Win32\SecretFile\SecretFile.lib and
+ object blib\arch\auto\Win32\SecretFile\SecretFile.exp
SecretFile.obj : error LNK2001: unresolved external symbol ConvertStri
+ngSecurityDescriptorToSecurityDescriptor
SecretFile.obj : error LNK2001: unresolved external symbol ConvertSidT
+oStringSid
blib\arch\auto\Win32\SecretFile\SecretFile.dll : fatal error LNK1120: 
+2 unresolved externals
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual S
+tudio 9.0\VC\Bin\amd64\link.EXE"' : return code '0x460'
Stop.
[download]

Which confuses me because in the exact same environment and using the same includes I build my code without errors:

C:\test>cl /W3 Permissions.c Advapi32.lib
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.21022.08 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

Permissions.c
Microsoft (R) Incremental Linker Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:Permissions.exe
Permissions.obj
Advapi32.lib
[download]

I have a work around that fixes the unresolved externals (but not the 'ConvertSidToStringSid' undefined; assuming extern returning int?); and that is to explicitly use the A versions of the two functions:

            if (ConvertSidToStringSidA(sid, &sid_as_string)) {
                PSECURITY_DESCRIPTOR sd = NULL;
                DWORD sd_size;
                SV *ssd_as_sv = sv_2mortal(newSVpvf(ssd_template, sid_
+as_string, sid_as_string));
                LocalFree(sid_as_string);
                if (ConvertStringSecurityDescriptorToSecurityDescripto
+rA(SvPV_nolen(ssd_as_sv),
                                                                      
+  SDDL_REVISION_1,
                                                                      
+  &sd, &sd_size)) {
[download]

The the build completes:

C:\test>pushd \perl64\packages\p5-Win32-SecretFile-master

C:\perl64\packages\p5-Win32-SecretFile-master>nmake install

Microsoft (R) Program Maintenance Utility Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

        C:\Perl64\bin\perl.exe C:\perl64\site\lib\ExtUtils\xsubpp  -ty
+pemap C:\Perl64\lib\ExtUtils\typemap  SecretFile.xs > SecretFile.xsc 
+&& C:\Perl64\bin\perl.exe -MExtUtils::Command -e mv -- SecretFile.xsc
+ SecretFile.c
Please specify prototyping behavior for SecretFile.xs (see perlxs manu
+al)
        cl -c  -I.  -nologo -GF -W3 -MD -Zi -Ox -GL -fp:precise -DWIN3
+2 -D_CONSOLE -DNO_STRICT -DHAVE_DES_FCRYPT -DWIN64 -DUSE_SITECUSTOMIZ
+E -DPRIVLIB_LAST_IN_INC -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -
+DUSE_PERLIO -DPERL_MSVCRT_READFIX -MD -Zi -Ox -GL -fp:precise    -DVE
+RSION=\"0.01\"  -DXS_VERSION=\"0.01\"  "-IC:\Perl64\lib\CORE"   Secre
+tFile.c
SecretFile.c
SecretFile.xs(55) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(58) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(58) : warning C4267: 'function' : conversion from 'size_
+t' to 'int', possible loss of data
SecretFile.xs(82) : warning C4013: 'ConvertSidToStringSidA' undefined;
+ assuming extern returning int
SecretFile.xs(87) : warning C4013: 'ConvertStringSecurityDescriptorToS
+ecurityDescriptorA' undefined; assuming extern returning int
SecretFile.xs(99) : warning C4267: 'function' : conversion from 'size_
+t' to 'DWORD', possible loss of data
        link -out:blib\arch\auto\Win32\SecretFile\SecretFile.dll -dll 
+-nologo -nodefaultlib -debug -opt:ref,icf -ltcg  -libpath:"C:\Perl64\
+lib\CORE"  -machine:AMD64 SecretFile.obj   C:\Perl64\lib\CORE\perl510
+.lib oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  com
+dlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib  netapi32.l
+ib uuid.lib ws2_32.lib mpr.lib winmm.lib  version.lib odbc32.lib odbc
+cp32.lib comctl32.lib bufferoverflowU.lib msvcrt.lib -def:SecretFile.
+def
   Creating library blib\arch\auto\Win32\SecretFile\SecretFile.lib and
+ object blib\arch\auto\Win32\SecretFile\SecretFile.exp
Generating code
Finished generating code
        if exist blib\arch\auto\Win32\SecretFile\SecretFile.dll.manife
+st mt -nologo -manifest blib\arch\auto\Win32\SecretFile\SecretFile.dl
+l.manifest -outputresource:blib\arch\auto\Win32\SecretFile\SecretFile
+.dll;2
        if exist blib\arch\auto\Win32\SecretFile\SecretFile.dll.manife
+st del blib\arch\auto\Win32\SecretFile\SecretFile.dll.manifest
        C:\Perl64\bin\perl.exe -MExtUtils::Command -e chmod -- 755 bli
+b\arch\auto\Win32\SecretFile\SecretFile.dll
Files found in blib\arch: installing files in blib\lib into architectu
+re dependent library tree
Installing C:\Perl64\site\lib\auto\Win32\SecretFile\SecretFile.dll
Installing C:\Perl64\site\lib\auto\Win32\SecretFile\SecretFile.exp
Installing C:\Perl64\site\lib\auto\Win32\SecretFile\SecretFile.lib
Installing C:\Perl64\site\lib\auto\Win32\SecretFile\SecretFile.pdb
Appending installation info to C:\Perl64\lib/perllocal.pod

C:\perl64\packages\p5-Win32-SecretFile-master>
[download]

And the code the runs:

C:\perl64\packages\p5-Win32-SecretFile-master>popd

C:\test>perl -MWin32::SecretFile -E"say Win32::SecretFile::_create_sec
+ret_file( 'mysecretfile.txt', 'Now is the time for all good men.', 0 
+);"
1

C:\test>type mysecretfile.txt
Now is the time for all good men.
C:\test>
[download]

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.