diff --git a/INSTALLATION.md b/INSTALLATION.md
index 1569b65..436299c 100644
--- a/INSTALLATION.md
+++ b/INSTALLATION.md
@@ -19,6 +19,7 @@ NOTE: Use either HCAPTCHA_ or RECAPTHCA_, not both.
 - ARGON_TIME - argon2 iterations
 - ARGON_KB - argon2 memory usage in KB
 - POW_DIFFICULTY - pow difficulty
+- POW_TYPE - type of ahsh algorithm for pow "argon2" or "sha256"
 
 #### Run in docker (for testing/development)
 
diff --git a/docker-compose.yml b/docker-compose.yml
index b5db76d..768642d 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -32,6 +32,7 @@ services:
       - ARGON_TIME=2
       - ARGON_KB=512
       - POW_DIFFICULTY=24
+      - POW_TYPE=argon2
       - TOR_CONTROL_PORT_PASSWORD=changeme
 
   nginx:
diff --git a/src/js/challenge.js b/src/js/challenge.js
index a678b34..4dcd4de 100644
--- a/src/js/challenge.js
+++ b/src/js/challenge.js
@@ -81,7 +81,7 @@ const powFinished = new Promise(resolve => {
 
 	window.addEventListener('DOMContentLoaded', async () => {
 
-		const { time, kb, pow, diff } = document.querySelector('[data-pow]').dataset;
+		const { time, kb, pow, diff, mode } = document.querySelector('[data-pow]').dataset;
 		window.addEventListener('storage', event => {
 			if (event.key === 'basedflare-pow-response' && !finished) {
 				console.log('Got answer', event.newValue, 'from storage event');
@@ -94,14 +94,15 @@ const powFinished = new Promise(resolve => {
 		});
 
 		if (!wasmSupported) {
-			return insertError('browser does not support WebAssembly.');
+			return insertError('Browser does not support WebAssembly.');
 		}
-		const argonOpts = {
+		const powOpts = {
 			time: time,
 			mem: kb,
 			hashLen: 32,
 			parallelism: 1,
-			type: argon2.ArgonType.Argon2id,
+			type: argon2 ? argon2.ArgonType.Argon2id : null,
+			mode: mode,
 		};
 		console.log('Got pow', pow, 'with difficulty', diff);
 		const eHashes = Math.pow(16, Math.floor(diff/8)) * ((diff%8)*2);
@@ -128,34 +129,16 @@ const powFinished = new Promise(resolve => {
 				submitPow(`${pow}#${answer}`);
 			}
 			for (let i = 0; i < workerThreads; i++) {
-				const argonWorker = new Worker('/.basedflare/js/worker.js');
-				argonWorker.onmessage = messageHandler;
-				workers.push(argonWorker);
+				const powWorker = new Worker('/.basedflare/js/worker.js');
+				powWorker.onmessage = messageHandler;
+				workers.push(powWorker);
 			}
 			for (let i = 0; i < workerThreads; i++) {
 				await new Promise(res => setTimeout(res, 10));
-				workers[i].postMessage([userkey, challenge, diff, diffString, argonOpts, i, workerThreads]);
+				workers[i].postMessage([userkey, challenge, diff, diffString, powOpts, i, workerThreads]);
 			}
 		} else {
-			//TODO: remove this section, it _will_ cause problems
-			console.warn('No webworker support, running in main/UI thread!');
-			let i = 0;
-			const start = Date.now();
-			while(true) {
-				const hash = await argon2.hash({
-					pass: challenge + i.toString(),
-					salt: userkey,
-					...argonOpts,
-				});
-				if (hash.hashHex.startsWith(diffString)
-					&& ((parseInt(hash.hashHex[diffString.length],16) &
-						0xff >> (((diffString.length+1)*8)-diff)) === 0)) {
-					console.log('Main thread found solution:', hash.hashHex, 'in', (Date.now()-start)+'ms');
-					break;
-				}
-				++i;
-			}
-			submitPow(`${pow}#${i}`);
+			return insertError('Browser does not support Web Workers.');
 		}
 	});
 }).then((powResponse) => {
diff --git a/src/js/worker.js b/src/js/worker.js
index b401b49..9a120f0 100644
--- a/src/js/worker.js
+++ b/src/js/worker.js
@@ -1,7 +1,15 @@
-importScripts('/.basedflare/js/argon2.js');
+async function nativeHash(data, method) {
+	const buffer = new TextEncoder('utf-8').encode(data);
+	const hashBuffer = await crypto.subtle.digest(method, buffer)
+	const hashArray = Array.from(new Uint8Array(hashBuffer));
+	return hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
+}
 
 onmessage = async function(e) {
-	const [userkey, challenge, diff, diffString, argonOpts, id, threads] = e.data;
+	const [userkey, challenge, diff, diffString, powOpts, id, threads] = e.data;
+	if (powOpts.mode === "argon2") {
+		importScripts('/.basedflare/js/argon2.js');
+	}
 	console.log('Worker thread', id, 'started');
 	let i = id;
 	if (id === 0) {
@@ -10,15 +18,21 @@ onmessage = async function(e) {
 		}, 500);
 	}
 	while(true) {
-		const hash = await argon2.hash({
-			pass: challenge + i.toString(),
-			salt: userkey,
-			...argonOpts,
-		});
+		let hash;
+		if (powOpts.mode === "argon2") {
+			const argonHash = await argon2.hash({
+				pass: challenge + i.toString(),
+				salt: userkey,
+				...powOpts,
+			});
+			hash = argonHash.hashHex;
+		} else {
+			hash = await nativeHash(userkey + challenge + i.toString(), 'sha-256');
+		}
 		// This throttle seems to really help some browsers not stop the workers abruptly
 		i % 10 === 0 && await new Promise(res => setTimeout(res, 10));
-		if (hash.hashHex.startsWith(diffString)
-			&& ((parseInt(hash.hashHex[diffString.length],16) &
+		if (hash.toString().startsWith(diffString)
+			&& ((parseInt(hash[diffString.length],16) &
 				0xff >> (((diffString.length+1)*8)-diff)) === 0)) {
 			console.log('Worker', id, 'found solution');
 			postMessage([id, i]);
diff --git a/src/lua/libs/utils.lua b/src/lua/libs/utils.lua
index eea98ff..00cd71a 100644
--- a/src/lua/libs/utils.lua
+++ b/src/lua/libs/utils.lua
@@ -43,6 +43,9 @@ end
 
 -- return true if hash passes difficulty
 function _M.checkdiff(hash, diff)
+	if #hash == 0 then
+		return false
+	end
 	local i = 1
 	for j = 0, (diff-8), 8 do
 		if hash:sub(i, i) ~= "0" then
diff --git a/src/lua/scripts/bot-check.lua b/src/lua/scripts/bot-check.lua
index c8e5236..f42b28a 100644
--- a/src/lua/scripts/bot-check.lua
+++ b/src/lua/scripts/bot-check.lua
@@ -9,13 +9,12 @@ local url = require("url")
 local utils = require("utils")
 local cookie = require("cookie")
 local json = require("json")
-local sha = require("sha")
 local randbytes = require("randbytes")
 local templates = require("templates")
 
 -- POW
+local pow_type = os.getenv("POW_TYPE") or "argon2"
 local pow_difficulty = tonumber(os.getenv("POW_DIFFICULTY") or 18)
-
 -- argon2
 local argon2 = require("argon2")
 local argon_kb = tonumber(os.getenv("ARGON_KB") or 6000)
@@ -25,9 +24,8 @@ argon2.m_cost(argon_kb)
 argon2.parallelism(1)
 argon2.hash_len(32)
 argon2.variant(argon2.variants.argon2_id)
-
 -- sha2
--- TODO
+local sha = require("sha")
 
 -- environment variables
 local captcha_secret = os.getenv("HCAPTCHA_SECRET") or os.getenv("RECAPTCHA_SECRET")
@@ -144,14 +142,20 @@ function _M.view(applet)
 				captcha_sitekey, captcha_script_src)
 		else
 			pow_body = templates.pow_section
-			noscript_extra_body = string.format(templates.noscript_extra, user_key,
+			local noscript_extra
+			if pow_type == "argon2" then
+				noscript_extra = templates.noscript_extra_argon2
+			else
+				noscript_extra = templates.noscript_extra_sha256
+			end
+			noscript_extra_body = string.format(noscript_extra, user_key,
 				challenge_hash, expiry, signature, math.ceil(pow_difficulty/8), 
 				argon_time, argon_kb)
 		end
 
 		-- sub in the body sections
 		response_body = string.format(templates.body, combined_challenge,
-			pow_difficulty, argon_time, argon_kb,
+			pow_difficulty, argon_time, argon_kb, pow_type,
 			site_name_body, pow_body, captcha_body, noscript_extra_body, ray_id)
 		response_status_code = 403
 
@@ -200,11 +204,14 @@ function _M.view(applet)
 						if given_signature == generated_signature then
 
 							-- do the work with their given answer
-							local full_hash = argon2.hash_encoded(given_challenge_hash .. given_answer, given_user_key)
-
-							-- check the output is correct
-							local hash_output = utils.split(full_hash, '$')[6]:sub(0, 43) -- https://github.com/thibaultcha/lua-argon2/issues/37
-							local hex_hash_output = sha.bin_to_hex(sha.base64_to_bin(hash_output));
+							local hex_hash_output = ""
+							if pow_type == "argon2" then
+								local encoded_argon_hash = argon2.hash_encoded(given_challenge_hash .. given_answer, given_user_key)
+								local trimmed_argon_hash = utils.split(encoded_argon_hash, '$')[6]:sub(0, 43) -- https://github.com/thibaultcha/lua-argon2/issues/37
+								hex_hash_output = sha.bin_to_hex(sha.base64_to_bin(trimmed_argon_hash));
+							else
+								hex_hash_output = sha.sha256(given_user_key .. given_challenge_hash .. given_answer)
+							end
 
 							if utils.checkdiff(hex_hash_output, pow_difficulty) then
 
diff --git a/src/lua/scripts/templates.lua b/src/lua/scripts/templates.lua
index 02fadb5..93e1b46 100644
--- a/src/lua/scripts/templates.lua
+++ b/src/lua/scripts/templates.lua
@@ -32,7 +32,7 @@ _M.body = [[
 		<script src="/.basedflare/js/argon2.js"></script>
 		<script src="/.basedflare/js/challenge.js"></script>
 	</head>
-	<body data-pow="%s" data-diff="%s" data-time="%s" data-kb="%s">
+	<body data-pow="%s" data-diff="%s" data-time="%s" data-kb="%s" data-mode="%s">
 		%s
 		%s
 		%s
@@ -50,7 +50,7 @@ _M.body = [[
 </html>
 ]]
 
-_M.noscript_extra = [[
+_M.noscript_extra_argon2 = [[
 			<details>
 				<summary>No JavaScript?</summary>
 				<ol>
@@ -68,6 +68,24 @@ _M.noscript_extra = [[
 			</details>
 ]]
 
+_M.noscript_extra_sha256 = [[
+			<details>
+				<summary>No JavaScript?</summary>
+				<ol>
+					<li>
+						<p>Run this in a linux terminal (requires <code>perl</code>):</p>
+						<code style="word-break: break-all;">
+							echo "dXNlIHN0cmljdDt1c2UgRGlnZXN0OjpTSEEgcXcoc2hhMjU2X2hleCk7cHJpbnQgIldvcmtpbmcuLi4iO215JGM9IiRBUkdWWzBdIi4iJEFSR1ZbMV0iO215JGlkPSRBUkdWWzRdKzA7bXkkZD0iMCJ4JGlkO215JGk9MDt3aGlsZSgxKXtsYXN0IGlmICRkIGVxIHN1YnN0ciBzaGEyNTZfaGV4KCRjLCRpKSwwLCRpZDskaSsrfXByaW50IlxuT3V0cHV0OlxuJEFSR1ZbMF0jJEFSR1ZbMV0jJEFSR1ZbMl0jJEFSR1ZbM10jJGlcbiI=" | base64 -d | perl -w - %s %s %s %s %s %s %s
+						</code>
+					<li>Paste the script output into the box and submit:
+					<form method="post">
+						<textarea name="pow_response" placeholder="script output" required></textarea>
+						<div><input type="submit" value="submit" /></div>
+					</form>
+				</ol>
+			</details>
+]]
+
 -- title with favicon and hostname
 _M.site_name_section = [[
 		<h3 class="pt">