(Ruby) 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.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require 'chilkat'

# 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.
# -----------------------------------------------------------------
prngClient = Chilkat::CkPrng.new()
eccClient = Chilkat::CkEcc.new()
privKeyClient = Chilkat::CkPrivateKey.new()
success = eccClient.GenKey("secp256r1",prngClient,privKeyClient)
if (success == false)
    print eccClient.lastErrorText() + "\n";
    exit
end

pubKeyClient = Chilkat::CkPublicKey.new()
privKeyClient.ToPublicKey(pubKeyClient)
pubKeyClient.SavePemFile(false,"qa_output/eccClientPub.pem")

# -----------------------------------------------------------------
# (Server-Side) Generate an ECC key, save the public part to a file.
# -----------------------------------------------------------------
prngServer = Chilkat::CkPrng.new()
eccServer = Chilkat::CkEcc.new()
privKeyServer = Chilkat::CkPrivateKey.new()
eccServer.GenKey("secp256r1",prngServer,privKeyServer)

pubKeyServer = Chilkat::CkPublicKey.new()
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.
pubKeyFromServer = Chilkat::CkPublicKey.new()
pubKeyFromServer.LoadFromFile("qa_output/eccServerPub.pem")
sharedSecret1 = 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.
pubKeyFromClient = Chilkat::CkPublicKey.new()
pubKeyFromClient.LoadFromFile("qa_output/eccClientPub.pem")
sharedSecret2 = eccServer.sharedSecretENC(privKeyServer,pubKeyFromClient,"base64")

# ---------------------------------------------------------
# Examine the shared secrets.  They should be the same.
# Both sides now have a secret that only they know.
# ---------------------------------------------------------
print sharedSecret1 + "\n";
print sharedSecret2 + "\n";