(Visual Basic 6.0) 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.

Note: This example requires Chilkat v11.0.0 or greater.

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Dim success As Long
success = 0

Dim cert As New ChilkatCert

' Load a digital certificate.
success = cert.LoadFromFile("digitalCert.cer")
If (success = 0) Then
    Debug.Print cert.LastErrorText
    Exit Sub
End If

' A .cer file does not contain the private key.  It should contain
' the public key...
Dim pubKey As New PublicKey
success = cert.GetPublicKey(pubKey)

' Let's have a look at it (in XML format).
Debug.Print "Public Key from Certificate:"
Debug.Print 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:
Dim privKey As New PrivateKey

success = privKey.LoadAnyFormatFile("PrivateKey.key","")
If (success <> 1) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
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...).
Debug.Print "Private Key from DER:"
Debug.Print privKey.GetXml()