add yard docs

lib/minisign/private_key.rb

@@ -8,6 +8,13 @@ class PrivateKey
                 :key_id, :public_key, :secret_key, :checksum
 
     # rubocop:disable Metrics/AbcSize
+    # rubocop:disable Layout/LineLength
+
+    # 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')
     def initialize(str, password = nil)
       contents = str.split("\n")
       bytes = Base64.decode64(contents.last).bytes
@@ -19,8 +26,10 @@ def initialize(str, password = nil)
       kdf_output = derive_key(password, @kdf_salt, @kdf_opslimit, @kdf_memlimit)
       @key_id, @secret_key, @public_key, @checksum = xor(kdf_output, bytes[54..157])
     end
+    # rubocop:enable Layout/LineLength
     # rubocop:enable Metrics/AbcSize
 
+    # @return [String] the <kdf_output> used to xor the ed25519 keys
     def derive_key(password, kdf_salt, kdf_opslimit, kdf_memlimit)
       RbNaCl::PasswordHash.scrypt(
         password,
@@ -31,17 +40,23 @@ def derive_key(password, kdf_salt, kdf_opslimit, kdf_memlimit)
       ).bytes
     end
 
+    # rubocop:disable Layout/LineLength
+
+    # @return [Array<32 bit unsigned ints>] the byte array containing the key id, the secret and public ed25519 keys, and the checksum
     def xor(kdf_output, contents)
+      # rubocop:enable Layout/LineLength
       xored = kdf_output.each_with_index.map do |b, i|
         contents[i] ^ b
       end
       [xored[0..7], xored[8..39], xored[40..71], xored[72..103]]
     end
 
+    # @return [Ed25519::SigningKey] the ed25519 signing key
     def ed25519_signing_key
       Ed25519::SigningKey.new(@secret_key.pack('C*'))
     end
 
+    # @return [String] the signature in the .minisig format that can be written to a file.
     def sign(filename, message)
       signature = ed25519_signing_key.sign(blake2b512(message))
       trusted_comment = "timestamp:#{Time.now.to_i}\tfile:#{filename}\thashed"