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TOTP-algorithm/Python-TOTP-algorithm.md

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+# Implementation of the TOTP algorithm in Python
+
+```Python
+from hashlib import sha1
+from datetime import datetime
+from base64 import b32decode
+
+INTERVAL = 30
+TOTP_KEY = "BOMY6BV5BWVJEWJ4ZLDYKN3LSIS736B3"
+
+def generate():
+    # Pre-process data
+    epoch = datetime.now().timestamp()
+    msg = int(epoch) // INTERVAL
+    bytes_msg = msg.to_bytes(8, byteorder="big")
+
+    key_decoded = b32decode(TOTP_KEY, casefold=True)
+
+    # HMAC-SHA1
+    key_pad = key_decoded.ljust(64, b"\0")
+    i_key_pad = bytes(x ^ 0x36 for x in key_pad)
+    o_key_pad = bytes(x ^ 0x5C for x in key_pad)
+    i_key_pad_msg = i_key_pad + bytes_msg
+    i_key_pad_msg_hashed = sha1(i_key_pad_msg).digest()
+    o_key_pad_msg = o_key_pad + i_key_pad_msg_hashed
+    hmac_result = sha1(o_key_pad_msg).digest()
+
+    # TOTP Algorithm
+    start = hmac_result[19] & 0xF
+    raw_bytes = hmac_result[start:start + 4]
+    raw_token = int.from_bytes(raw_bytes, byteorder="big")
+    raw_token = raw_token & 0x7F_FF_FF_FF
+    token = raw_token % 1_000_000
+
+    print(str(token).rjust(6, "0"))
+
+```