The authors propose a strategy called "Griefing-Penalty", which compensates intermediaries affected by the attack. The loss incurred upon mounting a griefing attack is proportional to the collateral cost of each channel involved in routing the payment. The authors illustrate the benefit of the proposed countermeasure with a new payment protocol called HTLC-GP (Hashed Timelock Contract with Griefing-Penalty), and provide a security analysis that proves the protocol is privacy-preserving while mitigating losses due to griefing attacks by compensating honest nodes. The problem with the current construction is that the adversary doesn't suffer any loss of funds when mounting a griefing attack. To penalize adversaries, the authors propose an off-chain contract established between two parties where both parties lock funds, with one party locking the amount to be forwarded and the other party locking the fund claimable as a penalty if it grieves. The penalty locked is proportional to the product of the amount being forwarded and the expiration time of the contract, and all parties affected by griefing must receive compensation since their liquidity is tied up for a certain period. An example was demonstrated where A wants to transfer 1 msat to C, but funds remain locked if C grieves. By modifying the contract, the authors term it HTLC-GP, where a rate of penalty (0.01 per hour) is used for calculating the penalty the party has to lock to accept an off-chain contract request. If C releases the preimage before the expiration of locktime, it will claim the full amount locked in the contract. In contrast, if C grieves, B must ask C to lock funds in the contract, which can be used for compensating both B and A. If C grieves under this condition, it loses 0.72 msat (proportional to the collateral cost of the path).