add option to change password for locked_secretbox in trees-create

bin/trees-create

@@ -27,6 +27,7 @@ end
 def usage
   puts "USAGE:"
   puts "   trees-create --password PASSWORD [OPTIONS]"
+  puts "   trees-create --password PASSWORD --old-password PASSWORD OPTIONS"
   puts
   puts "OPTIONS may include:"
   puts "   --opslimit OPSLIMIT     -- argon2 ops limit, integer in 3..10, or one of"
@@ -37,6 +38,9 @@ def usage
   puts "                              #{StorageKey::SALT_BYTES} bytes in length"
   puts "   --nonce NONCE           -- hex encoded nonce for secretbox encryption of"
   puts "                              private key, #{StorageKey::NONCE_BYTES} bytes in length"
+  puts "   --secretbox SECRETBOX   -- hex encoded secretbox"
+  puts
+  puts "for password change all options are required"
   exit 1
 end
 
@@ -46,6 +50,9 @@ def main
 
   while ARGV.any?
     case ARGV.first
+    when "--old-password"
+      ARGV.shift
+      old_password = ARGV.shift
     when "--password"
       ARGV.shift
       password = ARGV.shift
@@ -61,12 +68,19 @@ def main
     when "--nonce"
       ARGV.shift
       st.sk_nonce = ARGV.shift
+    when "--secretbox"
+      ARGV.shift
+      st.locked_secretbox = ARGV.shift
     else
       usage
     end
   end
   usage unless password
+  if old_password.nil?
     st.generate_new_keypair(password)
+  else
+    st.change_password(old_password, password)
+  end
   puts st.to_s
 end
 
@@ -121,6 +135,14 @@ class StorageKey
     )
   end
 
+  def change_password(old_password, password)
+    key = self.decrypt_key(old_password)
+    self.encrypt_key(
+      key: key,
+      password: password
+    )
+  end
+
   def to_s
     attrs = [:public_key, :locked_secretbox, :sk_nonce, :pwhash_opslimit,
              :pwhash_memlimit, :pwhash_salt]