(VBScript) About RSA Public/Private Keys

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts.

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Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Cert")
set cert = CreateObject("Chilkat.Cert")

' Load a digital certificate.
success = cert.LoadFromFile("digitalCert.cer")
If (success <> 1) Then
    outFile.WriteLine(cert.LastErrorText)
    WScript.Quit
End If

' A .cer file does not contain the private key.  It should contain
' the public key...
' pubKey is a Chilkat.PublicKey
Set pubKey = cert.ExportPublicKey()

' Let's have a look at it (in XML format).
outFile.WriteLine("Public Key from Certificate:")
outFile.WriteLine(pubKey.GetXml())

' An RSA public key consists of a modulus and exponent.

' An RSA private key includes both the modulus and exponent,
' as well as other "big" numbers: P, Q, D, etc.

' Let's load an RSA private key from a DER-encoded file:
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.PrivateKey")
set privKey = CreateObject("Chilkat.PrivateKey")

success = privKey.LoadAnyFormatFile("PrivateKey.key","")
If (success <> 1) Then
    outFile.WriteLine(privKey.LastErrorText)

    WScript.Quit
End If

' If this private key is the matching half to the public key from
' the certificate, then the modulus and exponent should
' be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
outFile.WriteLine("Private Key from DER:")
outFile.WriteLine(privKey.GetXml())


outFile.Close