diff --git a/src/main.js b/src/main.js
--- a/src/main.js
+++ b/src/main.js
@@ -4,6 +4,7 @@ import {pbkdf2} from "./pbkdf2.js";
 import {Chacha20,encrypt as _encrypt,decrypt as _decrypt} from "./chacha.js";
 
 const VERSION=1;
+const MAX_ITERS=24;
 
 function encrypt(s,password){
 	let bs=util.str2utf8(s);
@@ -25,10 +26,12 @@ function decrypt(s,password){
 	let salt=arr.slice(18,30);
 	let ciphertext=arr.slice(30);
 	
+	if(ciphertext.length==0){return 4;}
+	if(version>VERSION){return 2;}
+	if(iters>MAX_ITERS){return 3;}
 	let key=pbkdf2(pass,salt,1<<iters,32);
 	let check=blake2s([version,iters].concat(salt,ciphertext),16,key);
 	if(!signature.every((b,i)=>b===check[i])){return 1;}
-	if(version>VERSION){return 2;}
 	let plainbytes=_decrypt(ciphertext,key,salt);
 	return util.utf82str(plainbytes);
 }
@@ -36,7 +39,7 @@ function decrypt(s,password){
 function stretchKey(password,salt){
 	let start=Date.now(); // ms
 	let i,key;
-	for(i=0;i<52;i++){
+	for(i=0;i<=MAX_ITERS;i++){
 		key=pbkdf2(password,salt,1<<i,32);
 		if(Date.now()-start>=500){break;}
 	}