Implement NIP-04: Encrypted Direct Messages

README.md

@@ -20,6 +20,7 @@ has not yet reached a stable release. Use with caution.
   * [Stop previous subscriptions](#stop-previous-subscriptions)
   * [Publishing an event](#publishing-an-event)
   * [Creating/updating your contact list](#creatingupdating-your-contact-list)
+  * [Sending an encrypted direct message](#sending-an-encrypted-direct-message)
 - [Implemented NIPs](#implemented-nips)
 - [Development](#development)
   * [Type checking](#type-checking)
@@ -240,6 +241,33 @@ update_contacts_event = user.create_event(
 client.publish(update_contacts_event)
 ```
 
+### Sending an encrypted direct message
+
+```ruby
+sender_private_key = '3185a47e3802f956ca5a2b4ea606c1d51c7610f239617e8f0f218d55bdf2b757'
+
+encrypted_direct_message = Nostr::Events::EncryptedDirectMessage.new(
+   sender_private_key: sender_private_key,
+   recipient_public_key: '6c31422248998e300a1a457167565da7d15d0da96651296ee2791c29c11b6aa0',
+   plain_text: 'Your feedback is appreciated, now pay $8',
+   previous_direct_message: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460' # optional
+)
+
+encrypted_direct_message.sign(sender_private_key)
+
+# #<Nostr::Events::EncryptedDirectMessage:0x0000000104c9fa68
+# @content="mjIFNo1sSP3KROE6QqhWnPSGAZRCuK7Np9X+88HSVSwwtFyiZ35msmEVoFgRpKx4?iv=YckChfS2oWCGpMt1uQ4GbQ==",
+#   @created_at=1676456512,
+#   @id="daac98826d5eb29f7c013b6160986c4baf4fe6d4b995df67c1b480fab1839a9b",
+#   @kind=4,
+#   @pubkey="8a9d69c56e3c691bec8f9565e4dcbe38ae1d88fffeec3ce66b9f47558a3aa8ca",
+#   @sig="028bb5f5bab0396e2065000c84a4bcce99e68b1a79bb1b91a84311546f49c5b67570b48d4a328a1827e7a8419d74451347d4f55011a196e71edab31aa3d6bdac",
+#   @tags=[["p", "6c31422248998e300a1a457167565da7d15d0da96651296ee2791c29c11b6aa0"], ["e", "ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460"]]>
+
+# Send it to the Relay
+client.publish(encrypted_direct_message)
+````
+
 ## Implemented NIPs
 
 - [x] [NIP-01 - Client](https://github.com/nostr-protocol/nips/blob/master/01.md)

Steepfile

@@ -6,7 +6,9 @@ target :lib do
   check 'lib'
 
   # Core libraries
+  library 'base64'
   library 'digest'
+  library 'openssl'
   library 'securerandom'
 
   # Gems

lib/nostr.rb

@@ -10,6 +10,7 @@ require_relative 'nostr/relay'
 require_relative 'nostr/key_pair'
 require_relative 'nostr/event_kind'
 require_relative 'nostr/event'
+require_relative 'nostr/events/encrypted_direct_message'
 require_relative 'nostr/client'
 require_relative 'nostr/user'
 

lib/nostr/crypto.rb

@@ -3,6 +3,72 @@
 module Nostr
   # Performs cryptographic operations on a +Nostr::Event+.
   class Crypto
+    # Numeric base of the OpenSSL big number used in an event content's encryption.
+    #
+    # @return [Integer]
+    #
+    BN_BASE = 16
+
+    # Name of the cipher curve used in an event content's encryption.
+    #
+    # @return [String]
+    #
+    CIPHER_CURVE = 'secp256k1'
+
+    # Name of the cipher algorithm used in an event content's encryption.
+    #
+    # @return [String]
+    #
+    CIPHER_ALGORITHM = 'aes-256-cbc'
+
+    # Encrypts a piece of text
+    #
+    # @api public
+    #
+    # @example Encrypting an event's content
+    #   crypto = Nostr::Crypto.new
+    #   encrypted = crypto.encrypt_text(sender_private_key, recipient_public_key, 'Feedback appreciated. Now pay $8')
+    #   encrypted # => "wrYQaHDfpOEvyJELSCg1vzsywmlJTz8NqH03eFW44s8iQs869jtSb26Lr4s23gmY?iv=v38vAJ3LlJAGZxbmWU4qAg=="
+    #
+    # @param sender_private_key [String] 32-bytes hex-encoded private key of the creator.
+    # @param recipient_public_key [String] 32-bytes hex-encoded public key of the recipient.
+    # @param plain_text [String] The text to be encrypted
+    #
+    # @return [String] Encrypted text.
+    #
+    def encrypt_text(sender_private_key, recipient_public_key, plain_text)
+      cipher = OpenSSL::Cipher.new(CIPHER_ALGORITHM).encrypt
+      cipher.iv = iv = cipher.random_iv
+      cipher.key = compute_shared_key(sender_private_key, recipient_public_key)
+      encrypted_text = cipher.update(plain_text) + cipher.final
+      encrypted_text = "#{Base64.encode64(encrypted_text)}?iv=#{Base64.encode64(iv)}"
+      encrypted_text.gsub("\n", '')
+    end
+
+    # Decrypts a piece of text
+    #
+    # @api public
+    #
+    # @example Encrypting an event's content
+    #   crypto = Nostr::Crypto.new
+    #   encrypted # => "wrYQaHDfpOEvyJELSCg1vzsywmlJTz8NqH03eFW44s8iQs869jtSb26Lr4s23gmY?iv=v38vAJ3LlJAGZxbmWU4qAg=="
+    #   decrypted = crypto.decrypt_text(recipient_private_key, sender_public_key, encrypted)
+    #
+    # @param sender_public_key [String] 32-bytes hex-encoded public key of the message creator.
+    # @param recipient_private_key [String] 32-bytes hex-encoded public key of the recipient.
+    # @param encrypted_text [String] The text to be decrypted
+    #
+    # @return [String] Decrypted text.
+    #
+    def decrypt_text(recipient_private_key, sender_public_key, encrypted_text)
+      base64_encoded_text, iv = encrypted_text.split('?iv=')
+      cipher = OpenSSL::Cipher.new(CIPHER_ALGORITHM).decrypt
+      cipher.iv = Base64.decode64(iv)
+      cipher.key = compute_shared_key(recipient_private_key, sender_public_key)
+      plain_text = cipher.update(Base64.decode64(base64_encoded_text)) + cipher.final
+      plain_text.force_encoding('UTF-8')
+    end
+
     # Uses the private key to generate an event id and sign the event
     #
     # @api public
@@ -33,6 +99,35 @@ module Nostr
 
     private
 
+    # Finds a shared key between two keys
+    #
+    # @api private
+    #
+    # @param private_key [String] 32-bytes hex-encoded private key.
+    # @param public_key [String] 32-bytes hex-encoded public key.
+    #
+    # @return [String] A shared key used in the event's content encryption and decryption.
+    #
+    def compute_shared_key(private_key, public_key)
+      group = OpenSSL::PKey::EC::Group.new(CIPHER_CURVE)
+
+      private_key_bn   = OpenSSL::BN.new(private_key, BN_BASE)
+      public_key_bn    = OpenSSL::BN.new("02#{public_key}", BN_BASE)
+      public_key_point = OpenSSL::PKey::EC::Point.new(group, public_key_bn)
+
+      asn1 = OpenSSL::ASN1::Sequence(
+        [
+          OpenSSL::ASN1::Integer.new(1),
+          OpenSSL::ASN1::OctetString(private_key_bn.to_s(2)),
+          OpenSSL::ASN1::ObjectId(CIPHER_CURVE, 0, :EXPLICIT),
+          OpenSSL::ASN1::BitString(public_key_point.to_octet_string(:uncompressed), 1, :EXPLICIT)
+        ]
+      )
+
+      pkey = OpenSSL::PKey::EC.new(asn1.to_der)
+      pkey.dh_compute_key(public_key_point)
+    end
+
     # Generates a SHA256 hash of a +Nostr::Event+
     #
     # @api private

lib/nostr/event_kind.rb

@@ -31,5 +31,13 @@ module Nostr
     # @return [Integer]
     #
     CONTACT_LIST = 3
+
+    # A special event with kind 4, meaning "encrypted direct message". An event of this kind has its +content+
+    # equal to the base64-encoded, aes-256-cbc encrypted string of anything a user wants to write, encrypted using a
+    # shared cipher generated by combining the recipient's public-key with the sender's private-key.
+    #
+    # @return [Integer]
+    #
+    ENCRYPTED_DIRECT_MESSAGE = 4
   end
 end

lib/nostr/events/encrypted_direct_message.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Classes of event kinds.
+  module Events
+    # An event whose +content+ is encrypted. It can only be decrypted by the owner of the private key that pairs
+    # the event's +pubkey+.
+    class EncryptedDirectMessage < Event
+      # Instantiates a new encrypted direct message
+      #
+      # @api public
+      #
+      # @example Instantiating a new encrypted direct message
+      #   Nostr::Events::EncryptedDirectMessage.new(
+      #    sender_private_key: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+      #    recipient_public_key: '48df4af6e240ac5f7c5de89bf5941b249880be0e87d03685b178ccb1a315f52e',
+      #    plain_text: 'Your feedback is appreciated, now pay $8',
+      # )
+      #
+      # @example Instantiating a new encrypted direct message that references a previous direct message
+      #   Nostr::Events::EncryptedDirectMessage.new(
+      #    sender_private_key: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460',
+      #    recipient_public_key: '48df4af6e240ac5f7c5de89bf5941b249880be0e87d03685b178ccb1a315f52e',
+      #    plain_text: 'Your feedback is appreciated, now pay $8',
+      #    previous_direct_message: 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460'
+      # )
+      #
+      # @param plain_text [String] The +content+ of the encrypted message.
+      # @param sender_private_key [String] 32-bytes hex-encoded private key of the message's author.
+      # @param recipient_public_key [String] 32-bytes hex-encoded public key of the recipient of the encrypted message.
+      # @param previous_direct_message [String] 32-bytes hex-encoded id identifying the previous message in a
+      # conversation or a message we are explicitly replying to (such that contextual, more organized conversations
+      # may happen
+      #
+      def initialize(plain_text:, sender_private_key:, recipient_public_key:, previous_direct_message: nil)
+        crypto = Crypto.new
+        keygen = Keygen.new
+
+        encrypted_content = crypto.encrypt_text(sender_private_key, recipient_public_key, plain_text)
+        sender_public_key = keygen.extract_public_key(sender_private_key)
+
+        super(
+          pubkey: sender_public_key,
+          kind: Nostr::EventKind::ENCRYPTED_DIRECT_MESSAGE,
+          content: encrypted_content,
+          )
+
+        add_pubkey_reference(recipient_public_key)
+        add_event_reference(previous_direct_message) if previous_direct_message
+      end
+    end
+  end
+end

sig/nostr/crypto.rbs

@@ -1,9 +1,16 @@
 module Nostr
   class Crypto
+    BN_BASE: Integer
+    CIPHER_CURVE: String
+    CIPHER_ALGORITHM: String
+
+    def encrypt_text: (String, String, String) -> String
+    def decrypt_text: (String, String, String) -> String
     def sign_event: (Event, String) -> Event
 
     private
 
+    def compute_shared_key: (String, String) -> String
     def hash_event:(Event) -> String
   end
 end

sig/nostr/event_kind.rbs

@@ -4,5 +4,6 @@ module Nostr
     TEXT_NOTE: Integer
     RECOMMEND_SERVER: Integer
     CONTACT_LIST: Integer
+    ENCRYPTED_DIRECT_MESSAGE: Integer
   end
 end

sig/nostr/events/encrypted_direct_message.rbs

@@ -0,0 +1,12 @@
+module Nostr
+  module Events
+    class EncryptedDirectMessage < Event
+      def initialize: (
+          plain_text: String,
+          sender_private_key: String,
+          recipient_public_key: String,
+          ?previous_direct_message: String|nil
+        ) -> void
+    end
+  end
+end

spec/nostr/crypto_spec.rb

@@ -30,4 +30,50 @@ RSpec.describe Nostr::Crypto do
       end
     end
   end
+
+  describe '#encrypt_text' do
+    let(:sender_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '8a9d69c56e3c691bec8f9565e4dcbe38ae1d88fffeec3ce66b9f47558a3aa8ca',
+        private_key: '3185a47e3802f956ca5a2b4ea606c1d51c7610f239617e8f0f218d55bdf2b757'
+      )
+    end
+
+    let(:recipient_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '6c31422248998e300a1a457167565da7d15d0da96651296ee2791c29c11b6aa0',
+        private_key: '22cea01c33eccf30fdd54cb6728f814f6de00c778aafd721e017f4582545f9cf'
+      )
+    end
+
+    it 'encrypts plain text' do
+      encrypted_text = crypto.encrypt_text(sender_keypair.private_key, recipient_keypair.public_key, 'Twitter Files')
+      decrypted_text = crypto.decrypt_text(recipient_keypair.private_key, sender_keypair.public_key, encrypted_text)
+
+      expect(decrypted_text).to eq('Twitter Files')
+    end
+  end
+
+  describe '#descrypt_text' do
+    let(:sender_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '8a9d69c56e3c691bec8f9565e4dcbe38ae1d88fffeec3ce66b9f47558a3aa8ca',
+        private_key: '3185a47e3802f956ca5a2b4ea606c1d51c7610f239617e8f0f218d55bdf2b757'
+      )
+    end
+
+    let(:recipient_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '6c31422248998e300a1a457167565da7d15d0da96651296ee2791c29c11b6aa0',
+        private_key: '22cea01c33eccf30fdd54cb6728f814f6de00c778aafd721e017f4582545f9cf'
+      )
+    end
+
+    it 'decrypts an encrypted text' do
+      encrypted_text = crypto.encrypt_text(sender_keypair.private_key, recipient_keypair.public_key, 'Twitter Files')
+      decrypted_text = crypto.decrypt_text(recipient_keypair.private_key, sender_keypair.public_key, encrypted_text)
+
+      expect(decrypted_text).to eq('Twitter Files')
+    end
+  end
 end

spec/nostr/event_kind_spec.rb

@@ -26,4 +26,10 @@ RSpec.describe Nostr::EventKind do
       expect(described_class::CONTACT_LIST).to eq(3)
     end
   end
+
+  describe '::ENCRYPTED_DIRECT_MESSAGE' do
+    it 'is an integer' do
+      expect(described_class::ENCRYPTED_DIRECT_MESSAGE).to eq(4)
+    end
+  end
 end

spec/nostr/events/encrypted_direct_message_spec.rb

@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Nostr::Events::EncryptedDirectMessage do
+  describe '.new' do
+    let(:sender_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '8a9d69c56e3c691bec8f9565e4dcbe38ae1d88fffeec3ce66b9f47558a3aa8ca',
+        private_key: '3185a47e3802f956ca5a2b4ea606c1d51c7610f239617e8f0f218d55bdf2b757'
+      )
+    end
+
+    let(:recipient_keypair) do
+      Nostr::KeyPair.new(
+        public_key: '6c31422248998e300a1a457167565da7d15d0da96651296ee2791c29c11b6aa0',
+        private_key: '22cea01c33eccf30fdd54cb6728f814f6de00c778aafd721e017f4582545f9cf'
+      )
+    end
+
+    let(:crypto) { Nostr::Crypto.new }
+
+    it 'creates an instance of an encrypted private message event that can be decrypted by its recipient' do
+      encrypted_direct_message = described_class.new(
+        sender_private_key: sender_keypair.private_key,
+        recipient_public_key: recipient_keypair.public_key,
+        plain_text: 'Your feedback is appreciated, now pay $8'
+      )
+
+      plain_text = crypto.decrypt_text(
+        recipient_keypair.private_key,
+        sender_keypair.public_key,
+        encrypted_direct_message.content
+      )
+
+      aggregate_failures do
+        expect(encrypted_direct_message.content).not_to eq(plain_text)
+        expect(plain_text).to eq('Your feedback is appreciated, now pay $8')
+      end
+    end
+
+    it 'adds a reference to the recipient in the tags' do
+      encrypted_direct_message = described_class.new(
+        sender_private_key: sender_keypair.private_key,
+        recipient_public_key: recipient_keypair.public_key,
+        plain_text: 'Your feedback is appreciated, now pay $8'
+      )
+
+      expect(encrypted_direct_message.tags).to eq([['p', recipient_keypair.public_key]])
+    end
+
+    context 'when previous_direct_message is omitted' do
+      it 'does not add a reference to a previous message' do
+        encrypted_direct_message = described_class.new(
+          sender_private_key: sender_keypair.private_key,
+          recipient_public_key: recipient_keypair.public_key,
+          plain_text: 'Your feedback is appreciated, now pay $8'
+        )
+
+        expect(encrypted_direct_message.tags).to eq([['p', recipient_keypair.public_key]])
+      end
+    end
+
+    context 'when previous_direct_message is given' do
+      let(:previous_direct_message_id) { 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460' }
+
+      it 'adds a reference to a previous message' do
+        encrypted_direct_message = described_class.new(
+          sender_private_key: sender_keypair.private_key,
+          recipient_public_key: recipient_keypair.public_key,
+          plain_text: 'Your feedback is appreciated, now pay $8',
+          previous_direct_message: previous_direct_message_id
+        )
+
+        expect(encrypted_direct_message.tags).to eq(
+          [
+            ['p', recipient_keypair.public_key],
+            ['e', previous_direct_message_id]
+          ]
+        )
+      end
+    end
+  end
+end