(Lianja) How to Generate an Elliptic Curve Shared Secret

Demonstrates how to generate an ECC (Elliptic Curve Cryptography) shared secret. Imagine a cilent has one ECC private key, the server has another. A shared secret is computed by each side providing it's public key to the other. The private keys are kept private.

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// This example includes both client-side and server-side code.
// Each code segment is marked as client-side or server-side.
// Imagine these segments are running on separate computers...

// -----------------------------------------------------------------
// (Client-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
loPrngClient = createobject("CkPrng")
loEccClient = createobject("CkEcc")
loPrivKeyClient = loEccClient.GenEccKey("secp256r1",loPrngClient)
if (loEccClient.LastMethodSuccess <> .T.) then
    ? loEccClient.LastErrorText
    release loPrngClient
    release loEccClient
    return
endif

loPubKeyClient = loPrivKeyClient.GetPublicKey()
loPubKeyClient.SavePemFile(.F.,"qa_output/eccClientPub.pem")
release loPubKeyClient

// -----------------------------------------------------------------
// (Server-Side) Generate an ECC key, save the public part to a file.
// -----------------------------------------------------------------
loPrngServer = createobject("CkPrng")
loEccServer = createobject("CkEcc")
loPrivKeyServer = loEccServer.GenEccKey("secp256r1",loPrngServer)
if (loEccServer.LastMethodSuccess <> .T.) then
    ? loEccServer.LastErrorText
    release loPrngClient
    release loEccClient
    release loPrngServer
    release loEccServer
    return
endif

loPubKeyServer = loPrivKeyServer.GetPublicKey()
loPubKeyServer.SavePemFile(.F.,"qa_output/eccServerPub.pem")
release loPubKeyServer

// -----------------------------------------------------------------
// (Client-Side) Generate the shared secret using our private key, and the other's public key.
// -----------------------------------------------------------------

// Imagine that the server sent the public key PEM to the client.
// (This is simulated by loading the server's public key from the file.
loPubKeyFromServer = createobject("CkPublicKey")
loPubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem")
lcSharedSecret1 = loEccClient.SharedSecretENC(loPrivKeyClient,loPubKeyFromServer,"base64")
release loPrivKeyClient

// -----------------------------------------------------------------
// (Server-Side) Generate the shared secret using our private key, and the other's public key.
// -----------------------------------------------------------------

// Imagine that the client sent the public key PEM to the server.
// (This is simulated by loading the client's public key from the file.
loPubKeyFromClient = createobject("CkPublicKey")
loPubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem")
lcSharedSecret2 = loEccServer.SharedSecretENC(loPrivKeyServer,loPubKeyFromClient,"base64")
release loPrivKeyServer

// ---------------------------------------------------------
// Examine the shared secrets.  They should be the same.
// Both sides now have a secret that only they know.
// ---------------------------------------------------------
? lcSharedSecret1
? lcSharedSecret2


release loPrngClient
release loEccClient
release loPrngServer
release loEccServer
release loPubKeyFromServer
release loPubKeyFromClient