(Visual FoxPro) 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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LOCAL loCert
LOCAL lnSuccess
LOCAL loPubKey
LOCAL loPrivKey

loCert = CreateObject('Chilkat_9_5_0.Cert')

*  Load a digital certificate.
lnSuccess = loCert.LoadFromFile("digitalCert.cer")
IF (lnSuccess <> 1) THEN
    ? loCert.LastErrorText
    RELEASE loCert
    CANCEL
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('Chilkat_9_5_0.PrivateKey')

lnSuccess = loPrivKey.LoadRsaDerFile("PrivateKey.key")
IF (lnSuccess <> 1) THEN
    ? loPrivKey.LastErrorText
    RELEASE loPubKey
    RELEASE loCert
    RELEASE loPrivKey
    CANCEL
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