(Ruby) About RSA Public/Private Keys

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts.

Note: This example requires Chilkat v11.0.0 or greater.

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

require 'chilkat'

success = false

cert = Chilkat::CkCert.new()

# Load a digital certificate.
success = cert.LoadFromFile("digitalCert.cer")
if (success == false)
    print cert.lastErrorText() + "\n";
    exit
end

# A .cer file does not contain the private key.  It should contain
# the public key...
pubKey = Chilkat::CkPublicKey.new()
cert.GetPublicKey(pubKey)

# Let's have a look at it (in XML format).
print "Public Key from Certificate:" + "\n";
print pubKey.getXml() + "\n";

# An RSA public key consists of a modulus and exponent.

# An RSA private key includes both the modulus and exponent,
# as well as other "big" numbers: P, Q, D, etc.

# Let's load an RSA private key from a DER-encoded file:
privKey = Chilkat::CkPrivateKey.new()

success = privKey.LoadAnyFormatFile("PrivateKey.key","")
if (success != true)
    print privKey.lastErrorText() + "\n";
    exit
end

# If this private key is the matching half to the public key from
# the certificate, then the modulus and exponent should
# be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
print "Private Key from DER:" + "\n";
print privKey.getXml() + "\n";