final Key spareKey2 = exchange.getAuxiliaryKey2();
spareKey1.copyTo(spareKey2);
final byte[] baseBytes = spareKey2.getEncodedBytes();
final int baseSize = spareKey2.getEncodedSize();
if (baseSize < elisionCount || elisionCount + length > Key.MAX_KEY_LENGTH) {
throw new InvalidKeyException("Key encoding in transaction is invalid");
}
System.arraycopy(bytes, offset, baseBytes, elisionCount, length);
spareKey2.setEncodedSize(elisionCount + length);
}