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Hotp
ASecurityHOTP (RFC 4226) HMAC-based one-time password reference. Counter- based OTP for hardware tokens. Covers algorithm step-by-step, Python implementation from scratch, pyotp/otpauth libraries, counter synchronization, resync protocol, look-ahead window, and security considerations vs TOTP.
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- Added September 7, 2026
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[](https://www.skillsdirectory.com/skills/bytesagain-hotp)---
name: hotp
version: 1.0.0
description: >
HOTP (RFC 4226) HMAC-based one-time password reference. Counter-
based OTP for hardware tokens. Covers algorithm step-by-step,
Python implementation from scratch, pyotp/otpauth libraries,
counter synchronization, resync protocol, look-ahead window,
and security considerations vs TOTP.
author: BytesAgain
homepage: https://bytesagain.com
source: https://github.com/bytesagain/ai-skills
tags: [hotp, otp, 2fa, authentication, security, rfc4226]
---
# HOTP Reference
HMAC-based one-time passwords.
## Commands
| Command | Description |
|---------|-------------|
| `intro` | Algorithm, HOTP vs TOTP |
| `implement` | Python/Node.js code |
| `security` | Counter sync, resync |
Files in this skill
- SKILL.md
- scripts/script.sh
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