move key id encoding

lib/minisign/public_key.rb

@@ -21,7 +21,7 @@ def initialize(str)
     #   public_key.key_id
     #   #=> "E86FECED695E8E0"
     def key_id
-      key_id_binary_string.bytes.map { |c| c.to_s(16) }.reverse.join.upcase
+      hex key_id_binary_string.bytes
     end
 
     # Verify a message's signature

lib/minisign/signature.rb

@@ -3,19 +3,21 @@
 module Minisign
   # Parse a .minisig file's contents
   class Signature
+    include Utils
     # @param str [String] The contents of the .minisig file
     # @example
     #   Minisign::Signature.new(File.read('test/example.txt.minisig'))
     def initialize(str)
       @lines = str.split("\n")
+      @decoded = Base64.strict_decode64(@lines[1])
     end
 
     # @return [String] the key id
     # @example
     #   Minisign::Signature.new(File.read('test/example.txt.minisig')).key_id
     #   #=> "E86FECED695E8E0"
     def key_id
-      encoded_signature[2..9].bytes.map { |c| c.to_s(16) }.reverse.join.upcase
+      hex @decoded[2..9].bytes
     end
 
     # @return [String] the trusted comment
@@ -33,18 +35,12 @@ def trusted_comment_signature
 
     # @return [String] the global signature
     def signature
-      encoded_signature[10..]
+      @decoded[10..]
     end
 
     # @return [String] The signature that can be written to a file
     def to_s
       "#{@lines.join("\n")}\n"
     end
-
-    private
-
-    def encoded_signature
-      Base64.decode64(@lines[1])
-    end
   end
 end

lib/minisign/utils.rb

@@ -18,6 +18,11 @@ def xor(kdf_output, contents)
       end
     end
 
+    # @return [String] bytes as little endian hexadecimal
+    def hex(bytes)
+      bytes.map { |c| c.to_s(16) }.reverse.join.upcase
+    end
+
     # @return [String] the <kdf_output> used to xor the ed25519 keys
     def derive_key(password, kdf_salt, kdf_opslimit, kdf_memlimit)
       RbNaCl::PasswordHash.scrypt(