Figure 2. Supporting KYC and AML for MP using cryptocurrency when a bank is involved. checker monitors transactions on the blockchain and within the bank system and can link them with credential information of involved parties to make sure that all KYC/AML requirements are satisfied. Case 2: MP for Merchant With a Cryptocurrency Account When both the payer and the merchant have cryptocurrency accounts, the two-step payment protocol can be applied and only three players are involved: the payer with a smart device to make payment, the merchant with a cryptocurrency account, and the blockchain-based cryptocurrency system. Figure 3 demonstrates the sketch of MP using cryptocurrency without a centralized bank using the two-step payment protocol. Figure 3. Reducing latency in cryptocurrency MP using smart devices without a centralized bank. The strategy is to use a two-step payment to shift the latency. March/April 2020 MP protocol for case 2 The MP protocol for case 2 leverages the two-step payment mechanism described in the section "Fine-Grained Payment Schemes," which works as follows. 1) Prepayment. The payer generates a set of prepayment records according to his/her preferences and submits them to the blockchain. 2) Payment request initialization. The merchant sends the payment request to the payer, which includes identity of the merchant, the value of the payment, and the merchant's digital signature that protects the authenticity/integrity of the request. The merchant can also share his/her preferred list of notaries with the payer. 3) Payment submission. The payer selects an adequate prepayment record according to information received from the merchant, and collaborate with the merchant to prepare the message to finish the selected prepayment. The message is then send to notaries listed in the prepayment record to confirm. 4) Payment confirmation. Notaries sign the message and submit it to the blockchain-based cryptocurrency system. The signed message is also sent to the merchant. The merchant does not need to wait for this transaction to be confirmed on the blockchain if he/she trusts those notaries as a group. The payer knows prepayment records he/she generated so he/she does not need to query the blockchain to obtain these information. For the merchant, he/she only needs to verify the confirmed payment record which is signed by a 31