Abstract .The basic principle of quantum mechanics1guarantees the unconditional security of quantum key distribution (QKD)2 , 3 , 4 , 5 , 6at the cost of forbidding the amplification of a quantum state. As a result, and despite remarkable progress in worldwide metropolitan QKD networks7 , 8over the past decades, a long-haul fibre QKD network without a trusted relay has not yet been achieved. Here, through the sending-or-not-sending protocol9, we achieve t...