diff --git a/manual.pdf b/manual.pdf
index c16fb56..5ab4caf 100644
Binary files a/manual.pdf and b/manual.pdf differ
diff --git a/src/misc.typ b/src/misc.typ
index 3a9178d..df51f3e 100644
--- a/src/misc.typ
+++ b/src/misc.typ
@@ -1,7 +1,8 @@
 #import "utils.typ": xor-bytes
 #import "sha.typ": sha1
 #import "md.typ": md4
-#import "utils.typ": utf8-to-utf16le
+#import "utils.typ": utf8-to-utf16le, z-fill
+#import "base.typ": b32-decode
 
 #let _compute-block-sized-key(key, hash-func: sha1, block-size: 64) = {
   if key.len() > block-size {
@@ -15,6 +16,18 @@
   return  key
 }
 
+#let _extract31(value) = {
+  let bytes = array(value)
+  let i = bytes.last().bit-and(0xf)
+  let selected-bytes = (
+    bytes.at(i).bit-and(0x7f),
+    bytes.at(i+1),
+    bytes.at(i+2),
+    bytes.at(i+3)
+  )
+  return selected-bytes.fold(0, (a, b) => a.bit-lshift(8).bit-or(b))
+}
+
 /// Hash-based Message Authentication Code
 /// ```example
 /// #bytes-to-hex(hmac("Key", "Hello World!"))
@@ -56,4 +69,50 @@
 /// -> bytes
 #let ntlm(password) = {
   return md4(utf8-to-utf16le(password))
+}
+
+/// Time-based One-Time Password
+/// ```example
+/// #let epoch = datetime(
+///   year: 1970, month: 1, day: 1,
+///   hour: 0, minute: 0, second: 0
+/// )
+/// #let date = datetime(
+///   year: 2025, month: 1, day: 4,
+///   hour: 12, minute: 53, second: 30
+/// )
+/// #totp(
+///   b32-encode(bytes("YOUPI")),
+///   (date - epoch).seconds()
+/// )
+/// ```
+/// -> str
+#let totp(
+  /// Secret key. Either bytes or a base32-encode value
+  /// -> str | bytes
+  secret,
+  /// Current time (seconds since t0)
+  /// -> int
+  time,
+  /// Time origin
+  /// -> int
+  t0: 0,
+  /// Code duration
+  /// -> int
+  period: 30,
+  /// Code length
+  /// -> int
+  digits: 6
+) = {
+  let secret = if type(secret) == str {b32-decode(secret)} else {secret}
+  assert(type(secret) == bytes, message: "secret must be a string or bytes, but is " + repr(type(secret)))
+
+  let count = int(calc.div-euclid(time - t0, period))
+  let count-bytes = count.to-bytes(endian: "big", size: 8)
+  
+  let digest = hmac(secret, count-bytes)
+  let hotp = _extract31(digest)
+  let code = calc.rem(hotp, calc.pow(10, digits))
+
+  return z-fill(str(code), digits)
 }
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