Allow reusable nonces.

examples/pwhash_selector.cr

@@ -43,7 +43,7 @@ loop do
 
   loop do
     # p pwhash
-    t = Time.measure { pwhash.store pass }.to_f
+    t = Time.measure { pwhash.create pass }.to_f
     ostr = "%7d" % pwhash.opslimit
     header << ostr if data.size == 2
     if t >= time_min

src/sodium/nonce.cr

@@ -10,8 +10,10 @@ module Sodium
 
     NONCE_SIZE = LibSodium::NONCE_SIZE.to_i
 
-    getter? used
-    @used = false
+    getter? used = false
+
+    # Only use with single use keys.
+    property? reusable = false
 
     # Returns bytes
     delegate to_slice, to: @bytes
@@ -37,7 +39,7 @@ module Sodium
 
     def used!
       raise Error::Reused.new("attempted nonce reuse") if @used
-      @used = true
+      @used = true unless @reusable
     end
   end
 end