ykchalresp (1)

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

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 mimicing mode, meaning two subsequent calls with the same challenge will result in different responses.

-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).

-V

print tool version and exit.

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 -a 303132333435363738393a3b3c3d3e3f40414243
 ...
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
$

Report ykchalresp bugs in \$2 \(laURL: \$1 \(ra\$3

The

YubiKeys can be obtained from