(Lianja) 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.

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loCert = createobject("CkCert")

// Load a digital certificate.
llSuccess = loCert.LoadFromFile("digitalCert.cer")
if (llSuccess <> .T.) then
    ? loCert.LastErrorText
    release loCert
    return
endif

// A .cer file does not contain the private key.  It should contain
// the public key...
loPubKey = loCert.ExportPublicKey()

// Let's have a look at it (in XML format).
? "Public Key from Certificate:"
? loPubKey.GetXml()

// 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:
loPrivKey = createobject("CkPrivateKey")

llSuccess = loPrivKey.LoadAnyFormatFile("PrivateKey.key","")
if (llSuccess <> .T.) then
    ? loPrivKey.LastErrorText
    release loPubKey
    release loCert
    release loPrivKey
    return
endif

// 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...).
? "Private Key from DER:"
? loPrivKey.GetXml()

release loPubKey


release loCert
release loPrivKey