feat: adds sha256 signatures to outgoing http requests

Gemfile

@@ -8,12 +8,12 @@ gem "chronic"
 gem "domain_name"
 gem "dotenv"
 gem "dynamic_form"
-gem "encrypto_signo"
 gem "execjs", "~> 2.7", "< 2.8"
 gem "gelf"
 gem "haml"
 gem "hashie"
 gem "highline", require: false
+gem "jwt"
 gem "kaminari"
 gem "klogger-logger"
 gem "konfig-config", "~> 3.0"

Gemfile.lock

@@ -112,7 +112,6 @@ GEM
       activemodel (> 5.2.0)
     email_validator (2.2.4)
       activemodel
-    encrypto_signo (1.0.0)
     erubi (1.12.0)
     execjs (2.7.0)
     factory_bot (6.4.6)
@@ -152,6 +151,8 @@ GEM
       bindata
       faraday (~> 2.0)
       faraday-follow_redirects
+    jwt (2.8.1)
+      base64
     kaminari (1.2.2)
       activesupport (>= 4.1.0)
       kaminari-actionview (= 1.2.2)
@@ -410,14 +411,14 @@ DEPENDENCIES
   domain_name
   dotenv
   dynamic_form
-  encrypto_signo
   execjs (~> 2.7, < 2.8)
   factory_bot_rails
   gelf
   haml
   hashie
   highline
   jquery-rails
+  jwt
   kaminari
   klogger-logger
   konfig-config (~> 3.0)

app/controllers/well_known_controller.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class WellKnownController < ApplicationController
+
+  layout false
+
+  skip_before_action :set_browser_id
+  skip_before_action :login_required
+  skip_before_action :set_timezone
+
+  def jwks
+    render json: JWT::JWK::Set.new(Postal.signer.jwk).export.to_json
+  end
+
+end

app/lib/dkim_header.rb

@@ -9,7 +9,7 @@ def initialize(domain, message)
       @dkim_identifier = domain.dkim_identifier
     else
       @domain_name = Postal::Config.dns.return_path_domain
-      @dkim_key = Postal.signing_key
+      @dkim_key = Postal.signer.private_key
       @dkim_identifier = Postal::Config.dns.dkim_identifier
     end
     @domain = domain

app/lib/signer.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require "base64"
+
+class Signer
+
+  # Create a new Signer
+  #
+  # @param [OpenSSL::PKey::RSA] private_key The private key to use for signing
+  # @return [Signer]
+  def initialize(private_key)
+    @private_key = private_key
+  end
+
+  # Return the private key
+  #
+  # @return [OpenSSL::PKey::RSA]
+  attr_reader :private_key
+
+  # Return the public key for the private key
+  #
+  # @return [OpenSSL::PKey::RSA]
+  def public_key
+    @private_key.public_key
+  end
+
+  # Sign the given data
+  #
+  # @param [String] data The data to sign
+  # @return [String] The signature
+  def sign(data)
+    private_key.sign(OpenSSL::Digest.new("SHA256"), data)
+  end
+
+  # Sign the given data and return a Base64-encoded signature
+  #
+  # @param [String] data The data to sign
+  # @return [String] The Base64-encoded signature
+  def sign64(data)
+    Base64.strict_encode64(sign(data))
+  end
+
+  # Return a JWK for the private key
+  #
+  # @return [JWT::JWK] The JWK
+  def jwk
+    @jwk ||= JWT::JWK.new(private_key, { use: "sig", alg: "RS256" })
+  end
+
+  # Sign the given data using SHA1 (for legacy use)
+  #
+  # @param [String] data The data to sign
+  # @return [String] The signature
+  def sha1_sign(data)
+    private_key.sign(OpenSSL::Digest.new("SHA1"), data)
+  end
+
+  # Sign the given data using SHA1 (for legacy use) and return a Base64-encoded string
+  #
+  # @param [String] data The data to sign
+  # @return [String] The signature
+  def sha1_sign64(data)
+    Base64.strict_encode64(sha1_sign(data))
+  end
+
+end

config/routes.rb

@@ -89,6 +89,8 @@
     get "auth/oidc/callback", to: "sessions#create_from_oidc"
   end
 
+  get ".well-known/jwks.json" => "well_known#jwks"
+
   get "ip" => "sessions#ip"
 
   root "organizations#index"

lib/postal/config.rb

@@ -98,12 +98,15 @@ def locker_name_with_suffix(suffix)
       "#{locker_name} #{suffix}"
     end
 
-    def signing_key
-      @signing_key ||= OpenSSL::PKey::RSA.new(File.read(Config.postal.signing_key_path))
+    def signer
+      @signer ||= begin
+        key = OpenSSL::PKey::RSA.new(File.read(Config.postal.signing_key_path))
+        Signer.new(key)
+      end
     end
 
     def rp_dkim_dns_record
-      public_key = signing_key.public_key.to_s.gsub(/-+[A-Z ]+-+\n/, "").gsub(/\n/, "")
+      public_key = signer.private_key.public_key.to_s.gsub(/-+[A-Z ]+-+\n/, "").gsub(/\n/, "")
       "v=DKIM1; t=s; h=sha256; p=#{public_key};"
     end
 

lib/postal/config_schema.rb

@@ -72,6 +72,11 @@ module Postal
         transform { |v| Postal.substitute_config_file_root(v) }
       end
 
+      string :signing_key_id do
+        description "The ID (KID) for the key used for signing"
+        default "postal"
+      end
+
       string :smtp_relays do
         array
         description "An array of SMTP relays in the format of smtp://host:port"

lib/postal/http.rb

@@ -40,8 +40,9 @@ def self.request(method, url, options = {})
       end
 
       if options[:sign]
-        signature = EncryptoSigno.sign(Postal.signing_key, request.body.to_s).gsub("\n", "")
-        request.add_field "X-Postal-Signature", signature
+        request.add_field "X-Postal-Signature-KID", Postal.signer.jwk.kid
+        request.add_field "X-Postal-Signature", Postal.signer.sha1_sign64(request.body.to_s)
+        request.add_field "X-Postal-Signature-256", Postal.signer.sign64(request.body.to_s)
       end
 
       request["User-Agent"] = options[:user_agent] || "Postal/#{Postal.version}"

spec/lib/postal_spec.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Postal do
+  describe "#signer" do
+    it "returns a signer with the installation's signing key" do
+      expect(Postal.signer).to be_a(Signer)
+      expect(Postal.signer.private_key.to_pem).to eq OpenSSL::PKey::RSA.new(File.read(Postal::Config.postal.signing_key_path)).to_pem
+    end
+  end
+end

spec/lib/signer_spec.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Signer do
+  STATIC_PRIVATE_KEY = OpenSSL::PKey::RSA.new(2048) # rubocop:disable Lint/ConstantDefinitionInBlock
+
+  subject(:signer) { described_class.new(STATIC_PRIVATE_KEY) }
+
+  describe "#private_key" do
+    it "returns the private key" do
+      expect(signer.private_key).to eq(STATIC_PRIVATE_KEY)
+    end
+  end
+
+  describe "#public_key" do
+    it "returns the public key" do
+      expect(signer.public_key.to_s).to eq(STATIC_PRIVATE_KEY.public_key.to_s)
+    end
+  end
+
+  describe "#sign" do
+    it "returns a valid signature" do
+      data = "hello world!"
+      signature = signer.sign(data)
+      expect(signature).to be_a(String)
+      verification = STATIC_PRIVATE_KEY.public_key.verify(OpenSSL::Digest.new("SHA256"),
+                                                          signature,
+                                                          data)
+      expect(verification).to be true
+    end
+  end
+
+  describe "#sign64" do
+    it "returns a valid Base64-encoded signature" do
+      data = "hello world!"
+      signature = signer.sign64(data)
+      expect(signature).to be_a(String)
+      verification = STATIC_PRIVATE_KEY.public_key.verify(OpenSSL::Digest.new("SHA256"),
+                                                          Base64.strict_decode64(signature),
+                                                          data)
+      expect(verification).to be true
+    end
+  end
+
+  describe "#jwk" do
+    it "returns a valid JWK" do
+      jwk = signer.jwk
+      expect(jwk).to be_a(JWT::JWK::RSA)
+    end
+  end
+
+  describe "#sha1_sign" do
+    it "returns a valid signature" do
+      data = "hello world!"
+      signature = signer.sha1_sign(data)
+      expect(signature).to be_a(String)
+      verification = STATIC_PRIVATE_KEY.public_key.verify(OpenSSL::Digest.new("SHA1"),
+                                                          signature,
+                                                          data)
+      expect(verification).to be true
+    end
+  end
+
+  describe "#sha1_sign64" do
+    it "returns a valid Base64-encoded signature" do
+      data = "hello world!"
+      signature = signer.sha1_sign64(data)
+      expect(signature).to be_a(String)
+      verification = STATIC_PRIVATE_KEY.public_key.verify(OpenSSL::Digest.new("SHA1"),
+                                                          Base64.strict_decode64(signature),
+                                                          data)
+      expect(verification).to be true
+    end
+  end
+end

spec/services/webhook_delivery_service_spec.rb

@@ -28,7 +28,9 @@
         }.to_json,
         headers: {
           "Content-Type" => "application/json",
-          "X-Postal-Signature" => /\A[a-z0-9\/+]+=*\z/i
+          "X-Postal-Signature" => /\A[a-z0-9\/+]+=*\z/i,
+          "X-Postal-Signature-256" => /\A[a-z0-9\/+]+=*\z/i,
+          "X-Postal-Signature-KID" => /\A[a-f0-9\/+]{64}\z/i
         }
       })
     end