http://lm.i2p/nojs/knowledge/monero-atomic-swaps?dismissNotice=true
Bob uses this hash as a seed from which he generates his own lockbox, and sends his LTC there, where it is also locked. Since the hash of Alice's key was used as the seed by which Bob's lockbox was made, she can use her key to claim the LTC in Bob's lockbox. Her key fits! But, using math voodoo magic, when she uses her key to open the LTC lock, she reveals the key to Bob, who can then use it to claim the BTC that she put in her lockbox.