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.
Scanned 9/7/2026
Install to Claude Code
Skills Directorynpx -y skills add bytesagain/ai-skills --skill hotp --agent claude-codeInstalls into .claude/skills of the current project.
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---
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 |
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