HOTP One-Time Password Generator
HOTP One-Time Password Generator: Computes HMAC-SHA1 across 8-byte big-endian counter value and performs dynamic truncation.
About this hotp one-time password generator
Computes HMAC-SHA1 across 8-byte big-endian counter value and performs dynamic truncation Runs entirely in-memory using Web Crypto primitives to keep sensitive tokens, certificates, and cryptographic keys secure from third-party interception.
Encoding & cryptographic principles
Generates one RFC 4226 HMAC-SHA-1 HOTP code from a shared secret and a non-negative safe-integer counter encoded as eight big-endian bytes. Dynamic truncation uses the low four bits of the final digest byte; the page accepts 6, 7, or 8 decimal digits and does not verify a token.
Worked verification example
Scenario: A security engineer generates counter-based HMAC-Based One-Time Passwords (RFC 4226).
Sample input:
Processing: The client-side engine parses the provided input, executes the transformation routine, and outputs the result in real time.
Illustrative output:
Security parameters & input constraints
The counter must be a non-negative safe integer and digits must be an integer from 6 through 8; defaults are counter 0 and six digits. The page generates one code only; it does not verify a token, manage counter resynchronization or store a shared secret. Base32 detection is conditional, so other secret text is treated as UTF-8.
Cryptographic digests, encoded strings, and signatures generated by HOTP One-Time Password Generator should be verified against target authentication systems before production use.
Client-side Web Crypto boundary
Key derivation, hashing, and encoding in HOTP One-Time Password Generator execute in local memory using Web Crypto APIs without remote socket transmission.
Cryptographic specifications & RFC standards
Technical specifications and cryptographic RFC standards governing algorithms and key representations:
HOTP One-Time Password Generator verification · Audit standards
How to use it
- Enter JSON with secret, counter and optional digits.
- Decode the secret as Base32 only when its alphabet and length match the page's Base32 rule; otherwise use UTF-8, then compute HMAC-SHA-1 over the 8-byte counter.
- Apply dynamic truncation and display a six-to-eight-digit code with metadata as JSON.
Frequently asked questions
How does HOTP Generator use the counter?+
It parses JSON secret, counter, and optional digits, then calculates an HMAC-SHA-1 HOTP code for that exact counter value.
What result should the documented example produce?+
The RFC 4226 secret at counter 0 and six digits produced 755224.
Does HOTP advance or store the counter?+
No. It reads the supplied counter only and does not persist or increment it. The calling system must manage synchronization and replay prevention.
Can TOTP and HOTP codes be substituted?+
No. TOTP derives its counter from time while HOTP uses an explicit event counter. Both sides must use the same scheme and parameters.