in src/main/java/org/apache/sling/discovery/base/connectors/ping/TopologyRequestValidator.java [493:505]
private Key getKey(int keyNo) throws UnsupportedEncodingException {
if(Math.abs(keyNo - getCurrentKey()) > 1 ) {
throw new IllegalArgumentException("Key has expired");
}
if (keys.containsKey(keyNo)) {
return keys.get(keyNo);
}
trimKeys();
SecretKeySpec key = new SecretKeySpec(hash(sharedKey + keyNo).getBytes("UTF-8"),
"HmacSHA256");
keys.put(keyNo, key);
return key;
}