Generate Time-Based 2FA Codes Online Generate time-based one-time passwords (TOTP) compatible with Google Authenticator.

The tool works by first decoding the Base32 secret using a custom `b32Dec` function that converts each character to its corresponding binary value based on the Base32 alphabet defined in the RFC 4648 standard. This decoded secret is then used as the key for computing the HMAC-SHA1 hash over an 8-byte big-endian buffer containing the time step counter, which is calculated by dividing the current Unix timestamp by the specified period and taking the floor of the result. The `crypto.subtle.importKey` function from the Web Crypto API is used to import the decoded secret as a raw key for use with the HMAC algorithm.

The tool then uses the `crypto.subtle.sign` function to compute the HMAC-SHA1 hash over the time step buffer, producing a signature that is subsequently truncated using dynamic truncation. This involves taking the last nibble of the signature to determine the offset into the signature where the 4-byte code will be extracted, masking the extracted bytes with `0x7FFFFFFF` to ensure they are unsigned, and then reducing the result modulo `10^digits` to produce a numeric code with the desired number of digits. The resulting Time-Based One-Time Password (TOTP) is displayed to the user along with a visual countdown indicating when it will expire.

The tool's use of React for building the user interface allows for efficient updates to the display as the time step counter changes, while the `useCallback` and `useEffect` hooks are used to manage the generation of new TOTP codes at regular intervals based on the specified period. The `copyToClipboard` function from the `@/lib/utils` module is also used to enable users to easily copy the generated TOTP code for use in other applications or systems that support time-based one-time passwords, such as Google Authenticator or other authenticator apps.