Refactor private key (#19)

.rspec

@@ -1 +1,2 @@
 --require spec_helper
+--format documentation

.rubocop.yml

@@ -1,5 +1,6 @@
 Metrics/BlockLength:
-  IgnoredMethods: ['describe', 'context']
+  AllowedMethods: ['describe', 'context']
 AllCops:
     NewCops: enable
     TargetRubyVersion: 2.7.7
+    SuggestExtensions: false

lib/minisign/private_key.rb

@@ -4,60 +4,45 @@ module Minisign
   # Parse ed25519 signing key from minisign private key
   class PrivateKey
     include Utils
-    attr_reader :signature_algorithm, :kdf_algorithm, :cksum_algorithm, :kdf_salt, :kdf_opslimit, :kdf_memlimit,
-                :key_id, :ed25519_public_key, :secret_key, :checksum
+    attr_reader :kdf_salt, :kdf_opslimit, :kdf_memlimit,
+                :key_id, :ed25519_public_key_bytes, :ed25519_private_key_bytes, :checksum
 
-    # rubocop:disable Metrics/AbcSize
     # rubocop:disable Layout/LineLength
-    # rubocop:disable Metrics/MethodLength
 
     # Parse signing information from the minisign private key
     #
     # @param str [String] The minisign private key
     # @example
-    #   Minisign::PrivateKey.new('RWRTY0IyEf+yYa5eAX38PgdrI3TMxwy+3sgzpgcZWQXhOKqdf9sAAAACAAAAAAAAAEAAAAAAHe8Olzttgk6k5pZyT3CyCTcTAV0bLN3kq5CUqhLjqSdYZ6oEWs/S7ztaephS+/jwnuOElLBKkg3Sd56jzyvMwL4qStNUTyPDqckNjniw2SlowmHN8n5NnR47gvqjo96E+vakpw8v5PE=', 'password')
+    #   Minisign::PrivateKey.new(
+    #     'RWRTY0IyEf+yYa5eAX38PgdrI3TMxwy+3sgzpgcZWQXhOKqdf9sAAAACAAAAAAAAAEAAAAAAHe8Olzttgk6k5pZyT3CyCTcTAV0bLN3kq5CUqhLjqSdYZ6oEWs/S7ztaephS+/jwnuOElLBKkg3Sd56jzyvMwL4qStNUTyPDqckNjniw2SlowmHN8n5NnR47gvqjo96E+vakpw8v5PE=',
+    #     'password'
+    #   )
     def initialize(str, password = nil)
-      contents = str.split("\n")
-      decoded = Base64.decode64(contents.last)
-      @untrusted_comment = contents.first.split('untrusted comment: ').last
-      bytes = decoded.bytes
-      @signature_algorithm, @kdf_algorithm, @cksum_algorithm =
-        [bytes[0..1], bytes[2..3], bytes[4..5]].map { |a| a.pack('U*') }
-      raise 'Missing password for encrypted key' if @kdf_algorithm.bytes.sum != 0 && password.nil?
-
-      @kdf_salt = bytes[6..37]
-      @kdf_opslimit = bytes[38..45].pack('V*').unpack('N*').sum
-      @kdf_memlimit = bytes[46..53].pack('V*').unpack('N*').sum
-      @keynum_sk = bytes[54..157].pack('C*')
-      @key_data_bytes = if password
-                          kdf_output = derive_key(password, @kdf_salt.pack('C*'), @kdf_opslimit, @kdf_memlimit)
-                          xor(kdf_output, bytes[54..157])
-                        else
-                          bytes[54..157]
-                        end
-      @key_id, @secret_key, @ed25519_public_key, @checksum = key_data(@key_data_bytes)
-      assert_keypair_match!
+      comment, data = str.split("\n")
+      @password = password
+      decoded = Base64.decode64(data)
+      @untrusted_comment = comment.split('untrusted comment: ').last
+      @bytes = decoded.bytes
+      @kdf_salt, @kdf_opslimit, @kdf_memlimit = scrypt_params(@bytes)
+      @key_id, @ed25519_private_key_bytes, @ed25519_public_key_bytes, @checksum = key_data(password, @bytes[54..157])
+      validate_key!
     end
     # rubocop:enable Layout/LineLength
-    # rubocop:enable Metrics/AbcSize
-    # rubocop:enable Metrics/MethodLength
 
-    # @raise [RuntimeError] if the extracted public key does not match the derived public key
-    def assert_keypair_match!
-      raise 'Wrong password for that key' if @ed25519_public_key != ed25519_signing_key.verify_key.to_bytes.bytes
+    def signature_algorithm
+      @bytes[0..1].pack('U*')
     end
 
-    def key_data(bytes)
-      [bytes[0..7], bytes[8..39], bytes[40..71], bytes[72..103]]
+    def kdf_algorithm
+      @bytes[2..3].pack('U*')
     end
 
-    # @return [Ed25519::SigningKey] the ed25519 signing key
-    def ed25519_signing_key
-      Ed25519::SigningKey.new(@secret_key.pack('C*'))
+    def cksum_algorithm
+      @bytes[4..5].pack('U*')
     end
 
     def public_key
-      data = Base64.strict_encode64("Ed#{@key_id.pack('C*')}#{ed25519_signing_key.verify_key.to_bytes}")
+      data = Base64.strict_encode64("Ed#{@key_id.pack('C*')}#{@ed25519_public_key_bytes.pack('C*')}")
       Minisign::PublicKey.new(data)
     end
 
@@ -85,8 +70,35 @@ def to_s
       kdf_salt = @kdf_salt.pack('C*')
       kdf_opslimit = [@kdf_opslimit, 0].pack('L*')
       kdf_memlimit = [@kdf_memlimit, 0].pack('L*')
-      data = "Ed#{kdf_algorithm}B2#{kdf_salt}#{kdf_opslimit}#{kdf_memlimit}#{@keynum_sk}"
+      keynum_sk = key_data(@password,
+                           @key_id + @ed25519_private_key_bytes + @ed25519_public_key_bytes + @checksum).flatten
+      data = "Ed#{kdf_algorithm}B2#{kdf_salt}#{kdf_opslimit}#{kdf_memlimit}#{keynum_sk.pack('C*')}"
       "untrusted comment: #{@untrusted_comment}\n#{Base64.strict_encode64(data)}\n"
     end
+
+    private
+
+    def scrypt_params(bytes)
+      [bytes[6..37], bytes[38..45].pack('V*').unpack('N*').sum, bytes[46..53].pack('V*').unpack('N*').sum]
+    end
+
+    # @raise [RuntimeError] if the extracted public key does not match the derived public key
+    def validate_key!
+      raise 'Missing password for encrypted key' if kdf_algorithm.bytes.sum != 0 && @password.nil?
+      raise 'Wrong password for that key' if @ed25519_public_key_bytes != ed25519_signing_key.verify_key.to_bytes.bytes
+    end
+
+    def key_data(password, bytes)
+      if password
+        kdf_output = derive_key(password, @kdf_salt.pack('C*'), @kdf_opslimit, @kdf_memlimit)
+        bytes = xor(kdf_output, bytes)
+      end
+      [bytes[0..7], bytes[8..39], bytes[40..71], bytes[72..103]]
+    end
+
+    # @return [Ed25519::SigningKey] the ed25519 signing key
+    def ed25519_signing_key
+      Ed25519::SigningKey.new(@ed25519_private_key_bytes.pack('C*'))
+    end
   end
 end

spec/minisign/private_key_spec.rb

@@ -53,14 +53,15 @@
     end
 
     it 'parses the public key' do
-      key = @private_key.ed25519_public_key
+      key = @private_key.ed25519_public_key_bytes
       expect(key).to eq([108, 35, 192, 26, 47, 128, 233, 165, 133, 38, 242, 5, 76, 55, 135, 40,
                          103, 72, 230, 43, 184, 117, 219, 37, 173, 250, 196, 122, 252, 174, 173, 140])
     end
 
     it 'parses the secret key' do
-      expect(@private_key.secret_key).to eq([65, 87, 110, 33, 168, 130, 118, 100, 249, 200, 160, 167, 47, 59, 141,
-                                             122, 156, 38, 80, 199, 139, 1, 21, 18, 116, 110, 204, 131, 199, 202, 181, 87]) # rubocop:disable Layout/LineLength
+      key = @private_key.ed25519_private_key_bytes
+      expect(key).to eq([65, 87, 110, 33, 168, 130, 118, 100, 249, 200, 160, 167, 47, 59, 141,
+                         122, 156, 38, 80, 199, 139, 1, 21, 18, 116, 110, 204, 131, 199, 202, 181, 87])
     end
 
     it 'parses the checksum' do
@@ -70,8 +71,8 @@
       key_data = [
         [69, 100],
         @private_key.key_id,
-        @private_key.secret_key,
-        @private_key.ed25519_public_key
+        @private_key.ed25519_private_key_bytes,
+        @private_key.ed25519_public_key_bytes
       ].inject(&:+).pack('C*')
 
       computed_checksum = blake2b256(key_data).bytes