(Excel) RSA Signature/Verify with .key and .cer

See more RSA Examples

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

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' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim privKey As Chilkat.PrivateKey
Set privKey = Chilkat.NewPrivateKey

' Load the private key from an RSA .key file:

success = privKey.LoadPemFile("privateKey.key")
If (success <> True) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

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

Dim rsa As Chilkat.Rsa
Set rsa = Chilkat.NewRsa

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

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


strData = "This is the string to be signed."

' Sign the string using the sha-1 hash algorithm.
' Other valid choices are "md2", "sha256", "sha384",
' "sha512", and "md5".

hexSig = rsa.SignStringENC(strData,"sha-1")

Debug.Print hexSig

' Load a digital certificate from a .cer file:
Dim cert As Chilkat.Cert
Set cert = Chilkat.NewCert

success = cert.LoadFromFile("myCert.cer")
If (success <> True) Then
    Debug.Print cert.LastErrorText
    Exit Sub
End If

Set pubKey = cert.ExportPublicKey()

' Now verify using a separate instance of the RSA object:
Dim rsa2 As Chilkat.Rsa
Set rsa2 = Chilkat.NewRsa

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

Debug.Print "Success."