---
name: "ykchalresp"
section: "1"
platform: "linux"
package: "yubikey-personalization"
version: "1.20.0-5"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ykchalresp"
---

# ykchalresp(1)

Perform challenge-response operation with YubiKey

## NAME

ykchalresp - Perform challenge-response operation with YubiKey

## SYNOPSIS

**ykchalresp** \[*-nkey*\] \[*-1* \| *-2*\] \[*-H* \| *-Y*\] \[*-N*\] \[*-x*\] \[*-v*\] \[*-6* \| *-8*\] \[*-t*\] \[*-iFILE*\] \[*-V*\] \[*-h*\]

## DESCRIPTION

Send a challenge to a YubiKey, and read the response. The YubiKey can be configured with two different C/R modes — the standard one is a 160 bits HMAC-SHA1, and the other is a YubiKey OTP mimicking mode, meaning two subsequent calls with the same challenge will result in different responses.

## OPTIONS

- **-nkey**

  send the challenge to the nth key found.

- **-1**

  send the challenge to slot 1. This is the default

- **-2**

  send the challenge to slot 2.

- **-H**

  send a 64 byte HMAC challenge. This is the default.

- **-Y**

  send a 6 byte Yubico OTP challenge.

- **-N**

  non-blocking mode — abort if the YubiKey is configured to require a key press before sending the response.

- **-x**

  challenge is hex encoded.

- **-v**

  enable verbose mode.

- **-6**

  output the response in OATH format, 6 digits.

- **-8**

  output the response in OATH format, 8 digits.

- **-t**

  use current time as challenge instead of reading challenge from command line (as in default TOTP mode, seconds since 1970-01-01 00:00:00 / 30 encoded as an 8 byte challenge).

- **-i***FILE*

  take challenge from FILE instead of as an argument. If file is - challenge is read from STDIN

- **-V**

  print tool version and exit.

## EXAMPLE

The YubiKey challenge-response operation can be demonstrated using the **NIST PUB 198 A.2** test vector.

First, program a YubiKey with the test vector :

```
$ ykpersonalize -2 -ochal-resp -ochal-hmac -ohmac-lt64 -a303132333435363738393a3b3c3d3e3f40414243
 ...
Commit? (y/n) [n]: y
$
```

Now, send the NIST test challenge to the YubiKey and verify the result matches the expected :

```
$ ykchalresp -2 'Sample #2'
0922d3405faa3d194f82a45830737d5cc6c75d24
$
```

## BUGS

Report ykchalresp bugs in the issue tracker https://github.com/Yubico/yubikey-personalization/issues

## SEE ALSO

The ykpersonalize home page https://developers.yubico.com/yubikey-personalization/

YubiKeys can be obtained from Yubico http://www.yubico.com/