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How to Generate an Elliptic Curve Shared Secret

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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. AutoIt

Local $bSuccess = False

; 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.
; -----------------------------------------------------------------
$oPrngClient = ObjCreate("Chilkat.Prng")
$oEccClient = ObjCreate("Chilkat.Ecc")
$oPrivKeyClient = ObjCreate("Chilkat.PrivateKey")
$bSuccess = $oEccClient.GenKey("secp256r1",$oPrngClient,$oPrivKeyClient)
If ($bSuccess = False) Then
    ConsoleWrite($oEccClient.LastErrorText & @CRLF)
    Exit
EndIf

$oPubKeyClient = ObjCreate("Chilkat.PublicKey")
$oPrivKeyClient.ToPublicKey($oPubKeyClient)
$oPubKeyClient.SavePemFile(False,"qa_output/eccClientPub.pem")

; -----------------------------------------------------------------
; (Server-Side) Generate an ECC key, save the public part to a file.
; -----------------------------------------------------------------
$oPrngServer = ObjCreate("Chilkat.Prng")
$oEccServer = ObjCreate("Chilkat.Ecc")
$oPrivKeyServer = ObjCreate("Chilkat.PrivateKey")
$oEccServer.GenKey("secp256r1",$oPrngServer,$oPrivKeyServer)

$oPubKeyServer = ObjCreate("Chilkat.PublicKey")
$oPrivKeyServer.ToPublicKey($oPubKeyServer)
$oPubKeyServer.SavePemFile(False,"qa_output/eccServerPub.pem")

; -----------------------------------------------------------------
; (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.
$oPubKeyFromServer = ObjCreate("Chilkat.PublicKey")
$oPubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem")
Local $sharedSecret1 = $oEccClient.SharedSecretENC($oPrivKeyClient,$oPubKeyFromServer,"base64")

; -----------------------------------------------------------------
; (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.
$oPubKeyFromClient = ObjCreate("Chilkat.PublicKey")
$oPubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem")
Local $sharedSecret2 = $oEccServer.SharedSecretENC($oPrivKeyServer,$oPubKeyFromClient,"base64")

; ---------------------------------------------------------
; Examine the shared secrets.  They should be the same.
; Both sides now have a secret that only they know.
; ---------------------------------------------------------
ConsoleWrite($sharedSecret1 & @CRLF)
ConsoleWrite($sharedSecret2 & @CRLF)