(Tcl) 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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load ./chilkat.dll

set cert [new_CkCert]

# Load a digital certificate.
set success [CkCert_LoadFromFile $cert "digitalCert.cer"]
if {$success != 1} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkCert $cert
    exit
}

# pubKey is a CkPublicKey

# A .cer file does not contain the private key.  It should contain
# the public key...
set pubKey [CkCert_ExportPublicKey $cert]

# Let's have a look at it (in XML format).
puts "Public Key from Certificate:"
puts [CkPublicKey_getXml $pubKey]

# 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:
set privKey [new_CkPrivateKey]

set success [CkPrivateKey_LoadAnyFormatFile $privKey "PrivateKey.key" ""]
if {$success != 1} then {
    puts [CkPrivateKey_lastErrorText $privKey]
    delete_CkPublicKey $pubKey

    delete_CkCert $cert
    delete_CkPrivateKey $privKey
    exit
}

# 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...).
puts "Private Key from DER:"
puts [CkPrivateKey_getXml $privKey]

delete_CkPublicKey $pubKey


delete_CkCert $cert
delete_CkPrivateKey $privKey