I never could get the "C type parser" of Win32::API to work. I always had more luck manually constructing the parameter string using the P and I chars, and then using unpack for strings passed in and out.

In your case, maybe the following construct works:

$function = Win32::API->new('NSLClientLibrary', 'XYZDecrypt', 'PPP', '
+I');

sub call_function {
    my ($value, $key, $encrypted) = @_;
    # Here we pad $value to the expected length, to avoid a buffer ove
+rrun
    # I guess that the result is at most as long as the encrypted stri
+ng
    $value = ' ' x length $encrypted;
    $function->( $value, $key, $encrypted );
    $value =~ s!\0.*!!; # we assume that the first \0 returned indicat
+es end of the string
    return $value
};
[download]

$value =~ s!\0.*!!; # we assume that the first \0 returned indicates end of the string

That is a pretty bad assumption. BSTRs are fixed length arrays of unsigned shorts with a prefix length and can contain multiple nulls.

See http://blogs.msdn.com/b/ericlippert/archive/2003/09/12/52976.aspx

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what is interesting is that the prefix length is a byte count and not a character count,although BSTR is always Unicode

So to find the end of the string you have to get to the stored length which is stored in the first 2 bytes

the example at : BSTR layout shows the byte count and the terminated nulls,both required by BSTR

Am I perhaps calling the function wrong or something? as I get a
Not a CODE reference at xx.pl line 14
which is where the $function is called in the sub routine

#!/usr/bin/perl 
use Win32::API;  

my $function = Win32::API->new('C:\XYZClientLibrary\x86\XYZClientLibra
+ry.dll', 'XYZDecrypt', 'PPP', 'I');

print call_function('9','8B3A06617FEC4276A5711FBA4861B467', '[000001]C
+0808FC9B3062D91E7B9B1D9A7B79216');

sub call_function {
    my ($value, $key, $encrypted) = @_;
    # Here we pad $value to the expected length, to avoid a buffer ove
+rrun
    # I guess that the result is at most as long as the encrypted stri
+ng
    $value = ' ' x length($encrypted);
    print (" $value, $key, $encrypted\n");
    $value = $function->( $value, $key, $encrypted );
    $value =~ s!\0.*!!; # we assume that the first \0 returned indicat
+es end of the string
    return $value
};
[download]

nmeijer:

Looking at the Win32::API docs, it looks like line 14 should be:

$value = $function->Call( $value, $key, $encrypted );
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.