How do I call New-Object for a constructor which takes a single array parameter?

Question

In PowerShell, I want to use New-Object to call a single-argument .Net constructor new X509Certificate2(byte[] byteArray). The problem is when I do this with a byte array from powershell, I get

New-Object : Cannot find an overload for "X509Certificate2" and the argument count: "516".

Solution 1

This approach to using new-object should work:

$cert = new-object System.Security.Cryptography.X509Certificates.X509Certificate `
      -ArgumentList @(,$bytes)

The trick is that PowerShell is expecting an array of constructor arguments. When there is only one argument and it is an array, it can confuse PowerShell's overload resolution algorithm. The code above helps it out by putting the byte array in an array with just that one element.

Update: in PowerShell >= v5 you can call the constructor directly like so:

$cert = [System.Security.Cryptography.X509Certificates.X509Certificate]::new($bytes)

Solution 2

Surprisingly to me, I tried this and it seems it works:

[byte[]] $certPublicBytes = something
$cert = [System.Security.Cryptography.X509Certificates.X509Certificate] $certPublicBytes
return $cert

I don't yet know by what magic it works, so your explanatory comments are appreciated. :)

(Note: I since found that using square-brackets-type-name as I did above, can also lead to other errors, such as 'Cannot convert value "System.Byte[]" to type "System.Security.Cryptography.X509Certificates.X509Certificate". Error: "Cannot find the requested object.' The explicit New-Object approach recommended by Keith seems better!)