(Excel) Get RSA Key Modulus from .cer or .key

Demonstrates how to get the RSA key modulus from either the certificate (.cer) or RSA key (.key). OpenSSL commands to do the same would be:

openssl x509 -inform DER -in "test.cer"  -modulus -noout 

openssl pkcs8 -inform DER -in​ "test.key"​ -outform PEM -passin pass:"12345​678a​"
   | openssl rsa -inform PEM -modulus -noout 

Download Excel Class Modules Chilkat Excel Class Modules

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


password = "12345678a"

success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password)
If (success <> True) Then
    Debug.Print privKey.LastErrorText
    Exit Sub
End If

Dim xml As Chilkat.Xml
Set xml = Chilkat.NewXml
Dim success As Boolean
success = xml.LoadXml(privKey.GetXml())

' The XML contains the parts of the key in base64.
Debug.Print "Private Key XML:"
Debug.Print xml.GetXml()

' We can get the base64 modulus like this:

modulus = xml.GetChildContent("Modulus")
Debug.Print "base64 modulus = "; modulus

' To convert to hex:
Dim binDat As Chilkat.BinData
Set binDat = Chilkat.NewBinData
success = binDat.AppendEncoded(modulus,"base64")

hexModulus = binDat.GetEncoded("hex")
Debug.Print "hex modulus = "; hexModulus

' Now get the modulus from the cert:
Dim cert As Chilkat.Cert
Set cert = Chilkat.NewCert

success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer")
If (success <> True) Then
    Debug.Print cert.LastErrorText
    Exit Sub
End If

' The cert contains the public key, which is composed of the
' modulus + exponent (for RSA keys).

Set pubKey = cert.ExportPublicKey()

success = xml.LoadXml(pubKey.GetXml())
Debug.Print "Public Key XML:"
Debug.Print xml.GetXml()

' Proceed in the same way as before....
modulus = xml.GetChildContent("Modulus")
Debug.Print "base64 modulus = "; modulus

' To convert to hex:
success = binDat.Clear()
success = binDat.AppendEncoded(modulus,"base64")
hexModulus = binDat.GetEncoded("hex")
Debug.Print "hex modulus = "; hexModulus