diff --git a/functions.lua b/functions.lua
index ed0abc1..db3f077 100644
--- a/functions.lua
+++ b/functions.lua
@@ -110,8 +110,22 @@ function otp.hmac(key, message)
     return hmac
 end
 
-function otp.generate_code(key, message)
-    local hmac = otp.hmac(key, message)
+local function left_pad(str, s, len)
+    while #str < len do
+        str = s .. str
+    end
+    return str
+end
+
+function otp.generate_totp(key, unix_time)
+    unix_time = unix_time or os.time()
+
+    local tx = 30
+    local ct = math.floor(unix_time / tx)
+    local counter = otp.write_uint64_be(ct)
+    local valid_seconds = ((ct * tx) + tx) - unix_time
+
+    local hmac = otp.hmac(key, counter)
 
     -- https://www.rfc-editor.org/rfc/rfc4226#section-5.4
     local offset = bitand(string.byte(hmac, #hmac), 0xF)
@@ -120,5 +134,33 @@ function otp.generate_code(key, message)
     value = bitor(value, lshift(string.byte(hmac, offset+3), 8))
     value = bitor(value, lshift(string.byte(hmac, offset+2), 16))
     value = bitor(value, lshift(bitand(string.byte(hmac, offset+1), 0x7F), 24))
-    return value % 10^6
+    local code = value % 10^6
+    local padded_code = left_pad("" .. code, "0", 6)
+
+    return padded_code, valid_seconds
+end
+
+function otp.create_qr_png(data)
+    local pixel_size = 3
+    local height = pixel_size * #data
+    local width = height
+
+    local png_data = {}
+    for _, row in ipairs(data) do
+        assert(#row == #data)
+        for _=1,pixel_size do
+            for _, v in ipairs(row) do
+                for _=1,pixel_size do
+                    if v > 0 then
+                        table.insert(png_data, 0xFF000000)
+                    else
+                        table.insert(png_data, 0xFFFFFFFF)
+                    end
+                end
+            end
+        end
+    end
+    assert(#png_data == width*height)
+
+    return minetest.encode_png(width, height, png_data, 2)
 end
\ No newline at end of file
diff --git a/functions.spec.lua b/functions.spec.lua
index f53a39d..e5d629e 100644
--- a/functions.spec.lua
+++ b/functions.spec.lua
@@ -27,17 +27,34 @@ mtt.register("otp.hmac", function(callback)
     callback()
 end)
 
-mtt.register("otp.generate_code", function(callback)
+mtt.register("otp.generate_totp", function(callback)
     local expected_code = 699847
     local secret_b32 = "N6JGKMEKU2E6HQMLLNMJKBRRGVQ2ZKV7"
     local secret = otp.basexx.from_base32(secret_b32)
     local unix_time = 1640995200
 
-    local tx = 30
-    local ct = math.floor(unix_time / tx)
-    local counter = otp.write_uint64_be(ct)
+    local code, valid_seconds = otp.generate_totp(secret, unix_time)
+    assert(code == ""..expected_code)
+    assert(valid_seconds > 0)
 
-    local code = otp.generate_code(secret, counter)
-    assert(code == expected_code)
+    code, valid_seconds = otp.generate_totp(secret)
+    print("Current code: " .. code .. " valid for " .. valid_seconds .. " seconds")
+    callback()
+end)
+
+mtt.register("otp.create_qr_png", function(callback)
+    local url = "otpauth://totp/abc:myaccount?algorithm=SHA1&digits=6&issuer=abc&period=30&"
+        .. "secret=N6JGKMEKU2E6HQMLLNMJKBRRGVQ2ZKV7"
+
+    local ok, code = otp.qrcode(url)
+    assert(ok)
+    assert(code)
+
+    local png = otp.create_qr_png(code)
+    assert(png)
+
+    local f = io.open(minetest.get_worldpath() .. "/qr.png", "w")
+    f:write(png)
+    f:close()
     callback()
 end)
\ No newline at end of file
diff --git a/init.lua b/init.lua
index 17533e2..4655975 100644
--- a/init.lua
+++ b/init.lua
@@ -15,5 +15,4 @@ dofile(MP.."/functions.lua")
 
 if minetest.get_modpath("mtt") and mtt.enabled then
     dofile(MP.."/functions.spec.lua")
-    dofile(MP.."/qrencode.spec.lua")
 end
\ No newline at end of file
diff --git a/qrencode.spec.lua b/qrencode.spec.lua
deleted file mode 100644
index fb48891..0000000
--- a/qrencode.spec.lua
+++ /dev/null
@@ -1,13 +0,0 @@
-
-mtt.register("otp.qrcode", function(callback)
-    assert(type(otp.qrcode) == "function")
-
-    local url = "otpauth://totp/abc:myaccount?algorithm=SHA1&digits=6&issuer=abc&period=30&"
-        .. "secret=N6JGKMEKU2E6HQMLLNMJKBRRGVQ2ZKV7"
-
-    local ok, code = otp.qrcode(url)
-    assert(ok)
-    assert(code)
-
-    callback()
-end)
\ No newline at end of file