Lightning, the death of BIP62, and Segregated Witness

Due to the malleability of transaction IDs (txids), there have been concerns about the security of the Lightning Network. However, Tadge Dryja proposed a new "sighash_noinput" functionality which allows for reliable spending from unconfirmed transactions without txid malleability. The hard-fork variant involves putting signatures in another parallel Merkle tree while the soft-fork plan involves having the scriptPubKey just be the 20-byte hash of the redeem script and the actual scriptSig in a separate Merkle tree committed elsewhere in the block. The Segregated Witness can also achieve this but is a large hard-fork change. Testnet-L has been created to test the malleability mitigation out.