RSA Signature/Verify with .key and .cer

Demonstrates how to use a .key file (private key) and digital certificate (.cer, public key) to create and verify an RSA signature.

Download Chilkat RSA ActiveX

Dim privKey As New PrivateKey

Dim success As Long

'  Load the private key from an RSA .key file:
success = privKey.LoadPemFile("privateKey.key")
If (success <> 1) Then
    MsgBox privKey.LastErrorText
    Exit Sub
End If

Dim privKeyXml As String
'  Get the private key in XML format:
privKeyXml = privKey.GetXml()

Dim rsa As New ChilkatRsa

'  Any string argument automatically begins the 30-day trial.

success = rsa.UnlockComponent("30-day trial")
If (success <> 1) Then
    MsgBox rsa.LastErrorText
    Exit Sub
End If

'  Import the private key into the RSA component:
success = rsa.ImportPrivateKey(privKeyXml)
If (success <> 1) Then
    MsgBox rsa.LastErrorText
    Exit Sub
End If

'  Create the signature as a hex string:
rsa.EncodingMode = "hex"

Dim strData As String
strData = "This is the string to be signed."

'  Sign the string using the sha-1 hash algorithm.
'  Other valid choices are "md2" and "md5".
Dim hexSig As String
hexSig = rsa.SignStringENC(strData,"sha-1")

Text1.Text = Text1.Text & hexSig & vbCrLf

'  Load a digital certificate from a .cer file:
Dim cert As New ChilkatCert

success = cert.LoadFromFile("myCert.cer")
If (success <> 1) Then
    MsgBox cert.LastErrorText
    Exit Sub
End If

Dim pubKey As PublicKey

Set pubKey = cert.ExportPublicKey()

'  Now verify using a separate instance of the RSA object:
Dim rsa2 As New ChilkatRsa

'  Import the public key into the RSA object:
success = rsa2.ImportPublicKey(pubKey.GetXml())
If (success <> 1) Then
    MsgBox rsa2.LastErrorText
    Exit Sub
End If

'  The signature is a hex string, so make sure the EncodingMode is correct:
rsa2.EncodingMode = "hex"

'  Verify the signature:
success = rsa2.VerifyStringENC(strData,"sha-1",hexSig)
If (success <> 1) Then
    MsgBox rsa2.LastErrorText
    Exit Sub
End If

MsgBox "Success."