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📜 [專欄新文章] Using MPC to Help Achieve Blockchain Privacy

✍️ Yahsin Huang

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This post answers some of the most commonly asked questions about using multi-party computation (MPC) in blockchains.

What is MPC?

Multi-party computation (MPC) is a cryptographic protocol that does a joint computation involving multiple parties over their inputs while keeping those inputs private.

A famous example of MPC is Yao’s Millionaires Problem. Two millionaires want to know who is richer without finding out information about each other’s actual wealth. Naively they can simply tell their wealth to a third party. Then the third party compares their wealth and lets them know who is richer. But then this option is undesirable because the third party learns the information of their wealth.

The challenge of Yao’s Millionaires Problem is the computation wouldn’t be able to have a result without the two parties’ private information. To get the end result, you need those information involved in the computation. But at the same time, you are not allowed to reveal those private information to the party who performs the computation. That’s the main problem that MPC wants to solve.

Why it matters in blockchain?

In the real world, not everyone’s a millionaire. Not everybody wishes to compare their assets and wealth with others. In the blockchain space, there’s a need to ensure the inputs are shielded from multiple parties for privacy purposes; hence, the need for MPC protocols.

If we look at the current landscape of the blockchain world, notice there are blockchains doing great for programmability, such as Ethereum blockchain, allowing developers to build great tools and applications on top of them. There are also blockchains doing great for privacy, such as ZCash blockchain, allowing users to send transactions in a privacy-preserving way.

However, there’s a lack of blockchains that are designed for maximum programmability with maximum privacy. That’s why a lot of folks are pushing forward the work on incorporating MPC protocols into blockchain designs.

Why ZK is not enough?

Zero Knowledge Proofs (ZKP) is great at shielding private information that involves only one party. ZKP alone cannot be applied to provide privacy in multiple-party settings, such as auctions or in the case of Yao’s Millionaires Problem. In those settings, computations would involve private inputs from multiple parties, and so ZKP wouldn’t be enough. We would need to turn to MPC to achieve that.

Recent developments in MPC

In his presentation “MPC as a Blockchain Confidentiality Layer,” Miller gave a high-level overview of how MPC can be viewed as a confidentiality layer for blockchains as illustrated in the slide. Credit: https://youtu.be/0VuBELYfChM

How does MPC work with blockchains?

HoneyBadgerMPC builds a sidechain that performs MPC protocol computation. The sidechain acts as a confidentiality layer to the public blockchain, where secret data is stored.

How can developers build MPC applications?

Developers are able to develop MPC applications with Ratel language. Writing Ratel feels very similar to writing Solidity contracts. The compiler compiles Ratel code into two parts: the Ethereum part, and the MPC as a sidechain part.

Ratel code looks like this: https://github.com/initc3/HoneyBadgerSwap/blob/coconut/ratel/trade.rl

Learn more about MPC as a sidechain

One of the biggest news this past month was you could now play with HoneyBadgerSwap’s demo website. HoneyBadgerSwap is basically a dark pool version of Uniswap using MPC. You will need some Kovan ETH to test it out. Yunqi Li (UIUC, IC3) made a great Medium story about HoneyBadgerSwap. Read it here: “HoneyBadgerSwap: Making MPC as a Sidechain,” published on April 22, 2021.

Watch a really great talk by Andrew Miller “MPC as a Blockchain Confidentiality Layer,” presented at the IC3 Blockchain Camp 2020, to understand the HoneyBadgerMPC protocol more.

If you are someone who would like to delve into the topic with textbooks, be sure to add the book “A Pragmatic Introduction to Secure Multi-Party Computation” to your reading list. The content is available in PDF.

Using MPC to Help Achieve Blockchain Privacy was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.

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‼️Breaking‼️突發‼️

美國財政部周四按《全球馬格尼茨基人權問責法》（The Global Magnitsky Act），宣佈制裁4名中國人及新疆公安局，其中包括新疆黨委書記陳全國、前政法委書記朱海侖、新疆維吾爾自治區政府副主席王明山，以及現任新疆維吾爾自治區公安廳黨委書記霍留軍，指他們涉及嚴重侵犯新疆少數民族的人權。

“Treasury Sanctions Chinese Entity and Officials Pursuant to Global Magnitsky Human Rights Accountability Act...

‼️Breaking‼️突發‼️

美國財政部周四按《全球馬格尼茨基人權問責法》（The Global Magnitsky Act），宣佈制裁4名中國人及新疆公安局，其中包括新疆黨委書記陳全國、前政法委書記朱海侖、新疆維吾爾自治區政府副主席王明山，以及現任新疆維吾爾自治區公安廳黨委書記霍留軍，指他們涉及嚴重侵犯新疆少數民族的人權。

“Treasury Sanctions Chinese Entity and Officials Pursuant to Global Magnitsky Human Rights Accountability Act
July 9, 2020

Washington – Today, the U.S. Department of the Treasury’s Office of Foreign Assets Control (OFAC) sanctioned one Chinese government entity and four current or former government officials in connection with serious rights abuses against ethnic minorities in the Xinjiang Uyghur Autonomous Region (XUAR). These designations include Chen Quanguo, the Communist Party Secretary of XUAR, and Zhu Hailun, a former Deputy Party Secretary of the XUAR. Also designated today is the Xinjiang Public Security Bureau (XPSB), as well as the current Director and Communist Party Secretary of the XPSB, Wang Mingshan, and the former Party Secretary of the XPSB, Huo Liujun. The entity and officials are being designated for their connection to serious human rights abuse against ethnic minorities in Xinjiang, which reportedly include mass arbitrary detention and severe physical abuse, among other serious abuses targeting Uyghurs, a Turkic Muslim population indigenous to Xinjiang, and other ethnic minorities in the region.

“The United States is committed to using the full breadth of its financial powers to hold human rights abusers accountable in Xinjiang and across the world,” said Secretary Steven T. Mnuchin.

This action is being taken pursuant to Executive Order (E.O.) 13818, “Blocking the Property of Persons Involved in Serious Human Rights Abuse or Corruption,” which builds upon and implements the Global Magnitsky Human Rights Accountability Act.

These designations are the latest U.S. government actions in an ongoing effort to deter human rights abuses in the Xinjiang region. On July 1, 2020, the U.S. Department of State, along with the U.S. Department of the Treasury, the U.S. Department of Commerce, and the U.S. Department of Homeland Security, issued the Xinjiang Supply Chain Business Advisory, advising businesses with potential supply chain exposure to Xinjiang to consider the reputational, economic, and legal risks of involvement with entities that engage in human rights abuses in Xinjiang, such as forced labor. On May 22, 2020, the U.S. Department of Commerce added nine PRC entities related to human rights abuses in the Xinjiang region to the Commerce Entity List; this action complemented the October 2019 addition to the Commerce Entity List of 28 entities engaged in the PRC repression campaign in the Xinjiang region. Also, in October 2019, the U.S. Department of State announced a visa restriction policy under section 212 (a)(3)(C) of the Immigration and Nationality Act for PRC and Chinese Communist Party (CCP) officials responsible for, or complicit in, human rights abuses in Xinjiang.

CHEN QUANGUO AND ZHU HAILUN

The Xinjiang region in western China is home to Uyghurs, ethnic Kazakhs, ethnic Kyrgyz, and other traditionally Muslim minority groups. XUAR is the regional government of Xinjiang and falls under the governance of the PRC. Chen Quanguo (Chen) is the Party Secretary of the XUAR, a position he was appointed to in 2016, following Chen’s notorious history of intensifying security operations in the Tibetan Autonomous Region to tighten control over the Tibetan ethnic minorities. While Chen was already known for his ability to control “ethnic unrest,” when he got to Xinjiang, he had a deputy who understood the Xinjiang region, Zhu Hailun (Zhu), who for the past few decades had held several positions in the Chinese Communist Party, prior to holding the position of Party Secretary of the Xinjiang Political and Legal Committee (XPLC) from 2016 to 2019. In this role, Zhu was responsible for maintaining internal security and law enforcement in the XUAR; while Zhu left this role in 2019, he still currently serves as the Deputy Secretary of Xinjiang’s People’s Congress, a regional legislative body. Following his arrival to the region, Chen began implementing a comprehensive surveillance, detention, and indoctrination program in Xinjiang, targeting Uyghurs and other ethnic minorities through the XPSB.

As a part of Chen’s plans, the large-scale construction of mass detention camps, labelled “training centers,” greatly escalated in 2017, and as the Party Secretary of the XPLC, Zhu established the policies and procedures for managing these detention camps with the purported goal of using the camps to fight terrorism and maintain stability. Zhu’s policies outlined how the detention camps would operate, to include not allowing “escapes” and “abnormal deaths.” At the same time, former detainees of these detention camps report that deaths occurred among fellow detainees after torture and abuse at the hands of the security officials. A large focus of these detention camps was constant surveillance, even while detainees remain totally cut off from the outside world.

Chen is being designated for being a foreign person who is or has been a leader or official of an entity, including any government entity, that has engaged in, or whose members have engaged in serious human rights abuse relating to the leader’s or official’s tenure, and Zhu is being designated for being a foreign person who is responsible for or complicit in, or has directly or indirectly engaged in, serious human rights abuse.

REPRESSION IN THE XUAR: XINJIANG PUBLIC SECURITY BUREAU, HUO LIUJUN, AND WANG MINGSHAN

Since at least late 2016, repressive tactics have been used by the XPSB against the Uyghurs and members of other ethnic minority groups in the region, including mass detentions and surveillance. The PRC’s surveillance has targeted members of religious and ethnic minority groups, as the Chinese government treats almost all expressions of faith as a sign of religious “extremism” or ethnic separatism. Targets of this surveillance are often detained and reportedly subjected to various methods of torture and “political reeducation.” According to press reporting, since at least 2017, more than one million Muslims have been held in these camps.

Under the command of Huo Liujun (Huo), leader of the XPSB from at least March 2017 to 2018, and Wang Mingshan (Wang), leader of the XPSB since at least May 2018, the XPSB has deployed the “Integrated Joint Operations Platform” (IJOP), an Artificial Intelligence (AI)-assisted computer system that created biometric records for millions of Uyghurs in the Xinjiang region. The XPSB, through the IJOP, uses digital surveillance systems to track Uyghurs’ movements and activities, to include surveilling who they interact with and what they read. In turn, IJOP uses this data to determine which persons could be potential threats; according to reports, some of these individuals are subsequently detained and sent to detention camps, being held indefinitely without charges or trial. The IJOP AI platform is one of the first examples of governments using AI for racial profiling. According to press reporting, the IJOP technology looks exclusively for Uyghurs, based on their appearance, and keeps records of their movements. The mass detention of Uyghurs is part of an effort by PRC authorities to use detentions and data-driven surveillance to create a police state in the Xinjiang region.

The XPSB is being designated for being a foreign person responsible for, or complicit in, or that has directly or indirectly engaged in, serious human rights abuse. Huo and Wang are each being designated for being a foreign person who is or has been a leader or official of an entity whose property and interests in property are blocked pursuant to E.O. 13818 as a result of activities related to the leaders’ or officials’ tenure.

SANCTIONS IMPLICATIONS

As a result of today’s action, all property and interests in property of the entity and individuals named above, and of any entities that are owned, directly or indirectly, 50 percent or more by them, individually, or with other blocked persons, that are in the United States or in the possession or control of U.S. persons, are blocked and must be reported to OFAC. Unless authorized by a general or specific license issued by OFAC or otherwise exempt, OFAC’s regulations generally prohibit all transactions by U.S. persons or within (or transiting) the United States that involve any property or interests in property of designated or otherwise blocked persons. The prohibitions include the making of any contribution or provision of funds, goods, or services by, to, or for the benefit of any blocked person or the receipt of any contribution or provision of funds, goods or services from any such person.

GLOBAL MAGNITSKY

Building upon the Global Magnitsky Human Rights Accountability Act, the President signed E.O. 13818 on December 20, 2017, in which the President found that the prevalence of human rights abuse and corruption that have their source, in whole or in substantial part, outside the United States, had reached such scope and gravity that it threatens the stability of international political and economic systems. Human rights abuse and corruption undermine the values that form an essential foundation of stable, secure, and functioning societies; have devastating impacts on individuals; weaken democratic institutions; degrade the rule of law; perpetuate violent conflicts; facilitate the activities of dangerous persons; and undermine economic markets. The United States seeks to impose tangible and significant consequences on those who commit serious human rights abuse or engage in corruption, as well as to protect the financial system of the United States from abuse by these same persons.”

https://home.treasury.gov/news/press-releases/sm1055

Primaries and Disqualifications (Lee Yee)

Elsie Leung said, not disclosing all of the provisions of the National Security Law (NSL) is to prevent invoking clashes in society, and that the Standing Committee of the National People’s Congress (NPCSC) has already conducted sufficient consultations with different sectors.

Without disclosing the provisions of the NSL, what was used to consult these different sectors? This point alone discloses how absolutely absurd the so-called “sufficient consultations”, “different sectors”, and frankly, her entire statement are.

There have been commotions in the online community around the suggestion of achieving international sanctions through large-scale disqualifications, focusing mainly on the contradictions between the pro-democracy camp’s primaries and a large number of candidates. Primaries mean an aggregation of votes, to avoid an overextended list of candidates who would be dividing up the votes and possibly leading to the reduction of the number of elected seats. Most of the pro-democracy camp, including young candidates, are supportive of having primaries. The primary selection mechanism stipulates that only the winners are able stand for election. Some suggested that even the losers from the primaries should go ahead and stand for election, and were criticized for violating the principles of primaries.

These principles, however, were drafted before the NSL. It was when the legal profession and some Democrats still believed there was room for negotiation, when the retired former Chief Justice Honorable Andrew Li Kwok-nang proposed to protect the implementation details within Hong Kong under the premise of accepting the NSL. Some Democrats also suggested to bring back Article 23 in place of the implementation of the NSL by NPC, or to adopt the sunset clause. If the Chinese Communist Party (CCP) is willing to bargain, the red line for disqualifications of candidates could be drawn at the absolute “anti-NSL”, while turning a blind eye towards the Democrats who are willing to negotiate, such that LegCo would continue to have “decorative” Democrats.

The CCP categorically rejected all bargaining, and Andrew Li accused the Hong Kong NSL as completely undermining the independent judicial power guaranteed by the Basic Law. Martin Lee stated that “the Hong Kong NSL must be resisted fully”, and “people whose attention is being diverted to the devil in the details have already fallen into the trap devised by the CCP”. Moderates who wish to main the current system, to avoid “scorching-earth”, are already at a dead end.

The complete societal rift induced by the NSL is simple: on one side, you have people who blindly support an NSL without any disclosed provisions, including the pro-Beijing camp and the voluntarily “visually-impaired”; on the other side, you have citizens who support democracy. According to a poll conducted by the Hong Kong Institute of Public Opinion at the end of last month, 96% of the “supporters of the pro-democracy camp” opposed the NSL, and only 1% supported the law; Among those who are “non supporters of the pro-democracy camp”, 62% expressed support towards having the NSL implemented by the NPC, but those who opposed still amounted to 29%.

This was a poll done a month ago. With those who were willing to negotiate being rejected at this point, the societal rift should be more apparent. The situation is clear: any participant of the pro-democracy camp’s primaries, given that they have not been too vocal about opposing the NSL, even if they do win the primaries, have are able to join the election without being disqualified, they could still end up not winning the election. If citizens are to woefully cast their votes for candidates who do not oppose the NSL, looking at the poll, there’s only a 1% chance among the “supporters of the pro-democracy camp”.

Another situation that is clear: those who have openly and clearly opposed the NSL and somehow escape the fate of disqualification of candidacy is almost impossible. Even if there were, the voters would be doubtful of the candidates’ true stance, leading to a slim chance of getting elected.

As such, for the pro-democracy candidates, it is almost impossible to either oppose the NSL or to be disqualified for opposing. This, is precisely why the original intent of an aggregation of votes through the mechanism of primaries is likely to fail.

Disregard the results of the primaries. Flood the election with a loud and clear message of anti-NSL from a whale of candidates. This is the only way out. Having all or the majority being disqualified would be an obvious deprivation of Hongkongers’ right to vote, a guaranteed way to get international attention.

How much of a shockwave will international sanctions send to the CCP? An opinion piece published in Taiwan suggested that a senior Chinese official who may be sanctioned by the US because of the Hong Kong NSL has hidden assets in the US that are worth as much as US$3.1 billion. In 2013, Snowden, a former CIA employee who is now in Russia, announced that Chinese officials’ foreign deposits amounted to US$4.8 trillion. In normal circumstances, cash holdings account for only one-third of total assets, meaning that the total assets should amount to tens of trillions of US dollars (Hong Kong’s foreign exchange reserves are only about US$440 billion). And these were figures from 7 years ago.

International sanctions are, inevitably, internationally “earth-scorching”, where the side carrying out the sanctions will also suffer immensely. Freezing the assets of sanctioned officials in foreign countries will not help the sanctioning parties at all. Senior Chinese officials could care less about the Basic Law and Hong Kong’s human rights, but to laugh off one’s own properties? This is Hong Kong’s “earth-scorching” bargaining chip.