B4X

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 

B4X

Dim success As Boolean = False

Dim privKey As ChilkatPrivateKey
privKey.Initialize("privKey")

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


Dim xml As ChilkatXml
xml.Initialize
xml.LoadXml(privKey.GetXml)

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

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

'  To convert to hex:
Dim binDat As ChilkatBinData
binDat.Initialize
binDat.AppendEncoded(modulus, "base64")
Dim hexModulus As String = binDat.GetEncoded("hex")
Log("hex modulus = " & hexModulus)

'  Now get the modulus from the cert:
Dim cert As ChilkatCert
cert.Initialize("cert")

success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer")
If success = False Then
    Log(cert.LastErrorText)
    Return
End If


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

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

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

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