pps-php

Single-Device Mode

Single-device mode is the default PPS authentication mode.

It uses one registered device key and automatic forward-secure key rotation.

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Flow

1. Server creates a challenge with a nonce.
2. Client increments the counter.
3. Client generates the next key pair.
4. Client signs the Pulse payload with the current key.
5. Client includes the next public key in the payload.
6. Server verifies the signature.
7. Server verifies the counter and rotation sequence.
8. Server updates the stored public key to the next public key.

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Example

use Pps\Client\AuthenticatorClient;
use Pps\Server\AuthenticationHandler;
use Pps\Server\ChallengeGenerator;
use Pps\Storage\InMemoryStorage;

$storage = new InMemoryStorage();
$rpId = 'example.com';

$generator = new ChallengeGenerator();
$challenge = $generator->create($rpId);

$client = new AuthenticatorClient($clientState);
$pulse = $client
    ->rpId($rpId)
    ->nonce($challenge->nonceB64u)
    ->createPulse();

$handler = new AuthenticationHandler($storage);
$result = $handler->verify(
    pulseToken: $pulse['token'],
    rpId: $rpId,
    nonceB64u: $challenge->nonceB64u,
    trustCode: $pulse['trust_code']
);

if ($result->ok) {
    $clientState = $pulse['new_client_state'];
}

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State Updates

After successful verification, the server updates:

current_pk = next_pk
key_seq = rot_seq
last_counter = pulse_counter

The client updates:

current_seed = next_seed
counter = pulse_counter
key_seq = rot_seq
pending_certs = pending_certs + new_rotation_certificate

After the server acknowledges success, the client may clear pending certificates.

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Security Notes

• The current private key should be deleted after rotation.
• The counter must increase monotonically.
• The nonce must be single-use.
• The rotation sequence must increase by exactly one.

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