Merge pull request net-ssh#946 from flux-benj/aes-gcm

feat: Add support for aes(128|256)gcm

.rubocop_todo.yml

@@ -235,7 +235,7 @@ Lint/UselessTimes:
 # Offense count: 205
 # Configuration parameters: IgnoredMethods, CountRepeatedAttributes.
 Metrics/AbcSize:
-  Max: 74
+  Max: 75
 
 # Offense count: 16
 # Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.

lib/net/ssh/transport/aes128_gcm.rb

@@ -0,0 +1,40 @@
+require 'net/ssh/transport/hmac/abstract'
+require 'net/ssh/transport/gcm_cipher'
+
+module Net::SSH::Transport
+  ## Implements the aes128-gcm@openssh cipher
+  class AES128_GCM
+    extend ::Net::SSH::Transport::GCMCipher
+
+    ## Implicit HMAC, do need to do anything
+    class ImplicitHMac < ::Net::SSH::Transport::HMAC::Abstract
+      def aead
+        true
+      end
+
+      def key_length
+        16
+      end
+    end
+
+    def implicit_mac
+      ImplicitHMac.new
+    end
+
+    def algo_name
+      'aes-128-gcm'
+    end
+
+    def name
+      'aes128-gcm@openssh.com'
+    end
+
+    #
+    # --- RFC 5647 ---
+    # K_LEN       AES key length                   16 octets
+    #
+    def self.key_length
+      16
+    end
+  end
+end

lib/net/ssh/transport/aes256_gcm.rb

@@ -0,0 +1,40 @@
+require 'net/ssh/transport/hmac/abstract'
+require 'net/ssh/transport/gcm_cipher'
+
+module Net::SSH::Transport
+  ## Implements the aes256-gcm@openssh cipher
+  class AES256_GCM
+    extend ::Net::SSH::Transport::GCMCipher
+
+    ## Implicit HMAC, do need to do anything
+    class ImplicitHMac < ::Net::SSH::Transport::HMAC::Abstract
+      def aead
+        true
+      end
+
+      def key_length
+        32
+      end
+    end
+
+    def implicit_mac
+      ImplicitHMac.new
+    end
+
+    def algo_name
+      'aes-256-gcm'
+    end
+
+    def name
+      'aes256-gcm@openssh.com'
+    end
+
+    #
+    # --- RFC 5647 ---
+    # K_LEN       AES key length                   32 octets
+    #
+    def self.key_length
+      32
+    end
+  end
+end

lib/net/ssh/transport/algorithms.rb

@@ -44,7 +44,11 @@ class Algorithms
                   diffie-hellman-group14-sha256
                   diffie-hellman-group14-sha1],
 
-          encryption: %w[aes256-ctr aes192-ctr aes128-ctr],
+          encryption: %w[aes256-ctr
+                         aes192-ctr
+                         aes128-ctr
+                         aes256-gcm@openssh.com
+                         aes128-gcm@openssh.com],
 
           hmac: %w[hmac-sha2-512-etm@openssh.com hmac-sha2-256-etm@openssh.com
                    hmac-sha2-512 hmac-sha2-256
@@ -492,6 +496,9 @@ def exchange_keys
               HMAC.get(hmac_server, mac_key_server, parameters)
             end
 
+          cipher_client.nonce = iv_client if mac_client.respond_to?(:aead) && mac_client.aead
+          cipher_server.nonce = iv_server if mac_server.respond_to?(:aead) && mac_client.aead
+
           session.configure_client cipher: cipher_client, hmac: mac_client,
                                    compression: normalize_compression_name(compression_client),
                                    compression_level: options[:compression_level],

lib/net/ssh/transport/cipher_factory.rb

@@ -1,5 +1,7 @@
 require 'openssl'
 require 'net/ssh/transport/ctr.rb'
+require 'net/ssh/transport/aes128_gcm'
+require 'net/ssh/transport/aes256_gcm'
 require 'net/ssh/transport/key_expander'
 require 'net/ssh/transport/identity_cipher'
 require 'net/ssh/transport/chacha20_poly1305_cipher_loader'
@@ -31,15 +33,15 @@ class CipherFactory
           'none' => 'none'
         }
 
-        SSH_TO_CLASS =
+        SSH_TO_CLASS = {
+          'aes256-gcm@openssh.com' => Net::SSH::Transport::AES256_GCM,
+          'aes128-gcm@openssh.com' => Net::SSH::Transport::AES128_GCM
+        }.tap do |hash|
           if Net::SSH::Transport::ChaCha20Poly1305CipherLoader::LOADED
-            {
-              'chacha20-poly1305@openssh.com' => Net::SSH::Transport::ChaCha20Poly1305Cipher
-            }
-          else
-            {
-            }
+            hash['chacha20-poly1305@openssh.com'] =
+              Net::SSH::Transport::ChaCha20Poly1305Cipher
           end
+        end
 
         # Returns true if the underlying OpenSSL library supports the given cipher,
         # and false otherwise.

lib/net/ssh/transport/gcm_cipher.rb

@@ -0,0 +1,207 @@
+require 'net/ssh/loggable'
+
+module Net
+  module SSH
+    module Transport
+      ## Extension module for aes(128|256)gcm ciphers
+      module GCMCipher
+        # rubocop:disable Metrics/AbcSize
+        def self.extended(orig)
+          # rubocop:disable Metrics/BlockLength
+          orig.class_eval do
+            include Net::SSH::Loggable
+
+            attr_reader   :cipher
+            attr_reader   :key
+            attr_accessor :nonce
+
+            #
+            # Semantically gcm cipher supplies the OpenSSL iv interface with a nonce
+            #   as it is not randomly generated due to being supplied from a counter.
+            # The RFC's use IV and nonce interchangeably.
+            #
+            def initialize(encrypt:, key:)
+              @cipher = OpenSSL::Cipher.new(algo_name)
+              @key    = key
+              key_len = @cipher.key_len
+              if key.size != key_len
+                error_message = "#{cipher_name}: keylength does not match"
+                error { error_message }
+                raise error_message
+              end
+              encrypt ? @cipher.encrypt : @cipher.decrypt
+              @cipher.key = key
+
+              @nonce = {
+                fixed: nil,
+                invocation_counter: 0
+              }
+            end
+
+            def update_cipher_mac(payload, _sequence_number)
+              #
+              # --- RFC 5647 7.3 ---
+              # When using AES-GCM with secure shell, the packet_length field is to
+              # be treated as additional authenticated data, not as plaintext.
+              #
+              length_data      = [payload.bytesize].pack('N')
+
+              cipher.auth_data = length_data
+
+              encrypted_data   = cipher.update(payload) << cipher.final
+
+              mac              = cipher.auth_tag
+
+              incr_nonce
+              length_data + encrypted_data + mac
+            end
+
+            #
+            # --- RFC 5647 ---
+            # uint32    packet_length;  // 0 <= packet_length < 2^32
+            #
+            def read_length(data, _sequence_number)
+              data.unpack1('N')
+            end
+
+            #
+            # --- RFC 5647 ---
+            # In AES-GCM secure shell, the inputs to the authenticated encryption
+            # are:
+            #  PT (Plain Text)
+            #      byte      padding_length; // 4 <= padding_length < 256
+            #      byte[n1]  payload;        // n1 = packet_length-padding_length-1
+            #      byte[n2]  random_padding; // n2 = padding_length
+            #  AAD (Additional Authenticated Data)
+            #      uint32    packet_length;  // 0 <= packet_length < 2^32
+            #  IV (Initialization Vector)
+            #      As described in section 7.1.
+            #  BK (Block Cipher Key)
+            #      The appropriate Encryption Key formed during the Key Exchange.
+            #
+            def read_and_mac(data, mac, _sequence_number)
+              # The authentication tag will be placed in the MAC field at the end of the packet
+
+              # OpenSSL does not verify auth tag length
+              # GCM mode allows arbitrary sizes for the auth_tag up to 128 bytes and a single
+              #   byte allows authentication to pass. If single byte auth tags are possible
+              #   an attacker would require no more than 256 attempts to forge a valid tag.
+              #
+              raise 'incorrect auth_tag length' unless mac.to_s.length == mac_length
+
+              packet_length    = data.unpack1('N')
+
+              cipher.auth_tag  = mac.to_s
+              cipher.auth_data = [packet_length].pack('N')
+
+              result = cipher.update(data[4...]) << cipher.final
+              incr_nonce
+              result
+            end
+
+            def mac_length
+              16
+            end
+
+            def block_size
+              16
+            end
+
+            def self.block_size
+              16
+            end
+
+            #
+            # --- RFC 5647 ---
+            # N_MIN       minimum nonce (IV) length        12 octets
+            # N_MAX       maximum nonce (IV) length        12 octets
+            #
+            def iv_len
+              12
+            end
+
+            #
+            # --- RFC 5288 ---
+            # Each value of the nonce_explicit MUST be distinct for each distinct
+            # invocation of the GCM encrypt function for any fixed key. Failure to
+            # meet this uniqueness requirement can significantly degrade security.
+            # The nonce_explicit MAY be the 64-bit sequence number.
+            #
+            # --- RFC 5116 ---
+            # (2.1) Applications that can generate distinct nonces SHOULD use the nonce
+            # formation method defined in Section 3.2, and MAY use any
+            # other method that meets the uniqueness requirement.
+            #
+            # (3.2) The following method to construct nonces is RECOMMENDED.
+            #
+            #  <- variable -> <- variable ->
+            #  - - - - - - -  - - - - - - -
+            # |    fixed     |    counter   |
+            #
+            # Initial octets consist of a fixed field and final octets consist of a
+            # Counter field. Implementations SHOULD support 12-octet nonces in which
+            # the Counter field is four octets long.
+            # The Counter fields of successive nonces form a monotonically increasing
+            # sequence, when those fields are regarded as unsignd integers in network
+            # byte order.
+            # The Counter part SHOULD be equal to zero for the first nonce and increment
+            # by one for each successive nonce that is generated.
+            # The Fixed field MUST remain constant for all nonces that are generated for
+            # a given encryption device.
+            #
+            # --- RFC 5647 ---
+            # The invocation field is treated as a 64-bit integer and is increment after
+            # each invocation of AES-GCM to process a binary packet.
+            # AES-GCM produces a keystream in blocks of 16-octets that is used to
+            # encrypt the plaintext. This keystream is produced by encrypting the
+            # following 16-octet data structure:
+            #
+            # uint32 fixed;              // 4 octets
+            # uint64 invocation_counter; // 8 octets
+            # unit32 block_counter;      // 4 octets
+            #
+            # The block_counter is initially set to one (1) and increment as each block
+            # of key is produced.
+            #
+            # The reader is reminded that SSH requires that the data to be encrypted
+            # MUST be padded out to a multiple of the block size (16-octets for AES-GCM).
+            #
+            def incr_nonce
+              return if nonce[:fixed].nil?
+
+              nonce[:invocation_counter] = [nonce[:invocation_counter].to_s.unpack1('B*').to_i(2) + 1].pack('Q>*')
+
+              apply_nonce
+            end
+
+            def nonce=(iv_s)
+              return if nonce[:fixed]
+
+              nonce[:fixed]              = iv_s[0...4]
+              nonce[:invocation_counter] = iv_s[4...12]
+
+              apply_nonce
+            end
+
+            def apply_nonce
+              cipher.iv = "#{nonce[:fixed]}#{nonce[:invocation_counter]}"
+            end
+
+            #
+            # --- RFC 5647 ---
+            # If AES-GCM is selected as the encryption algorithm for a given
+            # tunnel, AES-GCM MUST also be selected as the Message Authentication
+            # Code (MAC) algorithm.  Conversely, if AES-GCM is selected as the MAC
+            # algorithm, it MUST also be selected as the encryption algorithm.
+            #
+            def implicit_mac?
+              true
+            end
+          end
+        end
+        # rubocop:enable Metrics/BlockLength
+      end
+      # rubocop:enable Metrics/AbcSize
+    end
+  end
+end

lib/net/ssh/transport/hmac/abstract.rb

@@ -8,6 +8,18 @@ module HMAC
         # The base class of all OpenSSL-based HMAC algorithm wrappers.
         class Abstract
           class << self
+            def aead(*v)
+              @aead = false if !defined?(@aead)
+              if v.empty?
+                @aead = superclass.aead if @aead.nil? && superclass.respond_to?(:aead)
+                return @aead
+              elsif v.length == 1
+                @aead = v.first
+              else
+                raise ArgumentError, "wrong number of arguments (#{v.length} for 1)"
+              end
+            end
+
             def etm(*v)
               @etm = false if !defined?(@etm)
               if v.empty?
@@ -57,6 +69,10 @@ def digest_class(*v)
             end
           end
 
+          def aead
+            self.class.aead
+          end
+
           def etm
             self.class.etm
           end