B4X Requires Chilkat v11.0.0+

How to Generate an Elliptic Curve Shared Secret

See more ECC Examples

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. B4X

Dim success As Boolean = 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.
'  -----------------------------------------------------------------
Dim prngClient As ChilkatPrng
prngClient.Initialize
Dim eccClient As ChilkatEcc
eccClient.Initialize
Dim privKeyClient As ChilkatPrivateKey
privKeyClient.Initialize("privKeyClient")
success = eccClient.GenKey("secp256r1", prngClient, privKeyClient)
If success = False Then
    Log(eccClient.LastErrorText)
    Return
End If

Dim pubKeyClient As ChilkatPublicKey
pubKeyClient.Initialize
privKeyClient.ToPublicKey(pubKeyClient)
pubKeyClient.SavePemFile(False, "qa_output/eccClientPub.pem")

'  -----------------------------------------------------------------
'  (Server-Side) Generate an ECC key, save the public part to a file.
'  -----------------------------------------------------------------
Dim prngServer As ChilkatPrng
prngServer.Initialize
Dim eccServer As ChilkatEcc
eccServer.Initialize
Dim privKeyServer As ChilkatPrivateKey
privKeyServer.Initialize("privKeyServer")
eccServer.GenKey("secp256r1", prngServer, privKeyServer)

Dim pubKeyServer As ChilkatPublicKey
pubKeyServer.Initialize
privKeyServer.ToPublicKey(pubKeyServer)
pubKeyServer.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.
Dim pubKeyFromServer As ChilkatPublicKey
pubKeyFromServer.Initialize
pubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem")
Dim sharedSecret1 As String = eccClient.SharedSecretENC(privKeyClient, pubKeyFromServer, "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.
Dim pubKeyFromClient As ChilkatPublicKey
pubKeyFromClient.Initialize
pubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem")
Dim sharedSecret2 As String = eccServer.SharedSecretENC(privKeyServer, pubKeyFromClient, "base64")

'  ---------------------------------------------------------
'  Examine the shared secrets.  They should be the same.
'  Both sides now have a secret that only they know.
'  ---------------------------------------------------------
Log(sharedSecret1)
Log(sharedSecret2)