VB.NET

Get RSA Key Modulus from .cer or .key

See more Certificates Examples

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 

or

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

VB.NET

Dim success As Boolean = False

Dim privKey As New Chilkat.PrivateKey

Dim password As String = "12345678a"
success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password)
If (success = False) Then
    Debug.WriteLine(privKey.LastErrorText)
    Exit Sub
End If


Dim xml As New Chilkat.Xml
xml.LoadXml(privKey.GetXml())

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

' We can get the base64 modulus like this:
Dim modulus As String = xml.GetChildContent("Modulus")
Debug.WriteLine("base64 modulus = " & modulus)

' To convert to hex:
Dim binDat As New Chilkat.BinData
binDat.AppendEncoded(modulus,"base64")
Dim hexModulus As String = binDat.GetEncoded("hex")
Debug.WriteLine("hex modulus = " & hexModulus)

' Now get the modulus from the cert:
Dim cert As New Chilkat.Cert

success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer")
If (success = False) Then
    Debug.WriteLine(cert.LastErrorText)
    Exit Sub
End If


' The cert contains the public key, which is composed of the
' modulus + exponent (for RSA keys).
Dim pubKey As New Chilkat.PublicKey
cert.GetPublicKey(pubKey)

xml.LoadXml(pubKey.GetXml())
Debug.WriteLine("Public Key XML:")
Debug.WriteLine(xml.GetXml())

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

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