(Ruby) 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 

Chilkat Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require 'chilkat'

privKey = Chilkat::CkPrivateKey.new()

password = "12345678a"
success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password)
if (success != true)
    print privKey.lastErrorText() + "\n";
    exit
end

xml = Chilkat::CkXml.new()
xml.LoadXml(privKey.getXml())

# The XML contains the parts of the key in base64.
print "Private Key XML:" + "\n";
print xml.getXml() + "\n";

# We can get the base64 modulus like this:
modulus = xml.getChildContent("Modulus")
print "base64 modulus = " + modulus + "\n";

# To convert to hex:
binDat = Chilkat::CkBinData.new()
binDat.AppendEncoded(modulus,"base64")
hexModulus = binDat.getEncoded("hex")
print "hex modulus = " + hexModulus + "\n";

# Now get the modulus from the cert:
cert = Chilkat::CkCert.new()

success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer")
if (success != true)
    print cert.lastErrorText() + "\n";
    exit
end

# The cert contains the public key, which is composed of the
# modulus + exponent (for RSA keys).
# pubKey is a CkPublicKey
pubKey = cert.ExportPublicKey()

xml.LoadXml(pubKey.getXml())
print "Public Key XML:" + "\n";
print xml.getXml() + "\n";

# Proceed in the same way as before....
modulus = xml.getChildContent("Modulus")
print "base64 modulus = " + modulus + "\n";

# To convert to hex:
binDat.Clear()
binDat.AppendEncoded(modulus,"base64")
hexModulus = binDat.getEncoded("hex")
print "hex modulus = " + hexModulus + "\n";