public_key_crypto.rb

require 'digest'

# INFO THAT THE SERVER KNOWS AND IS SHARED WITH THE CLIENT

# Public and secret keys are defined on the server level and shared
# only with the person who has the account.
PUBLIC_KEY = "PUBLIK"
SECRET_KEY = "SEKRET"

CLIENTS = {
	PUBLIC_KEY => SECRET_KEY,
	# other clients could be in here as well
}


# HOW WEB REQUESTS ARE PROCESSED (generally in a controller)

# Web Request Comes in to 
# www.myapp.com/?client=PUBLIK&t=1439240175&token=04f49831e1b524a1cbeca7ad73d97f2e1746b9ead6f6651b63a2317854357f6d

# URL parses out two pieces from the request
timestamp = params[:t] # 1439240175
client    = params[:client] #"PUBLIK" 

secret_key = CLIENTS[client]
token = Digest::SHA256.hexdigest("#{timestamp} #{secret_key}")

# Determine how long ago the timestamp was generated
minutes_ago = (Time.now - Time.at(params[:t])) / 60

# if the token didn't match or was too long ago, no dice
if params[:token] != token || minutes_ago > 5
	render :text => 'Not Allowed, Sucker!'
end