School of Business and Finance, Waseda University Senior Researcher / Lecturer, SFC / KMD, Keio University Chief Science Officer, BlockchainHub Inc. Representative Director, Beyond Blockchain Representative Director, Academy Camp Bio M.Eng in Computer Science from Cornell University, 1993 Ph.D. in Media and Governance from Keio University, 2006 (on digital currency research) Researcher of P2P (Peer-to-Peer) and digital currency for 19 years at Keio University (Just started my career at Waseda last September) Holding Academy Camp for children in Fukushima with friends since summer 2011 2018 Summer “OK Google, Do My Homework!” 2019 Winter “Automation for Girls” 2019 Summer “REINVENT THE WORLD” 2020 Spring “STAY HOME, ENJOY LIFE” (in Zoom) → Inter-connected in my mind (society hereafter needs to be designed with children) Blockchain : What For? — 2020-06-25 – p.3/28
technology? For example, I saw on the news quantum computer will dramatically increase the speed of calculating Therefore, the bitcoin might be no longer valuable in this sense ⇒ Short answer is, we have like 10 years to make changes in the technology But perhaps not because of the reason you mentioned In Bitcoin blockchain, nothing is encrypted But if you mean compromising cryptographic hash functions and/or digital signatures with quantum algorithms, Yes, that’s the reason why We will cover cryptographic basics later in this talk Blockchain : What For? — 2020-06-25 – p.5/28
benefit of blockchain concretely For example, why decenterlization is good for our daily life? ⇒ Good question! If monetary system is centralized (it is), for example, someday your bank account may be frozen for no particular reason That’s exactly why Bitcoin was invented It doesn’t mean that we cannot stop Bitcoin Blockchain : What For? — 2020-06-25 – p.6/28
an individual node is attacked, won’t the information eventually leak out? ⇒ Nothing is perfect for security But then again in Bitcoin blockchain, nothing is encrypted So we don’t worry about information leaking out It is true that with Bitcoin we can maintain some level of anonymity, But anonymity is not Bitcoin’s or blockchain’s main goal, And the technology is not really good at maintaining anonymity Blockchain : What For? — 2020-06-25 – p.7/28
prove, in effect, that the records have not been tampered with For detail, please search for WBS’s “FinTech (2019 Fall)” materials https://speakerdeck.com/ks91 Hopefully, it will provide a solution to the following essential problems with digital signatures Elapsed-Time Problem: “Did the signature allegedly applied in the past really exist from that time?” Alibi Problem: “Did the signature that was allegedly not applied in the past really not exist at the time?” The reason why these are problematic is that time can be spoofed, and if the private key is compromised or the signature technology itself is compromised, you can recreate the signature at any point in the past, or the signed data may be erased in the first place Therefore, digital signatures (or their absense) in the past cannot be trusted in general The real value of blockchain is “the ability to prove the existence or non-existence and authenticity of a previously signed digital signature without relying on any authority” Can you imagine applications for that? Blockchain : What For? — 2020-06-25 – p.9/28
NBUDIUIFEJHFTU DPNQVUFEGSPNUIFQMBJOUFYU %FDSZQUXQSJWBUFLFZ BTJGJU`TBOFODSZQUFEEBUB 3FDFJWFS 4FOEFS QMBJOUFYU QMBJOUFYU TJHOBUVSF TJHOBUVSF %JTUSJCVUFQVCMJDLFZTJOBEWBODF LFZQBJS EJHFTU QVCMJDLFZ QSJWBUFLFZ EJHFTU Can prove that it was sent by the very person and has not been altered This illustration shows how it works with RSA (RSA : Rivest, Shamir, Adleman) Instead, ECDSA is used in Bitcoin, etc. (Elliptic Curve DSA : Digital Signature Algorithm) Blockchain : What For? — 2020-06-25 – p.12/28
Output : signature Verifying Input : <plain text, signature, public key> Output : OK or NG Whether the signature meets certain mathematical properties that can be tested using plain text and public key Private key cannot be inferred in the verification process Blockchain : What For? — 2020-06-25 – p.13/28
nobody stop anyone from spending their own money (no denial of transactions) → (Payment) records can be proven (that they have not been altered) Proven = independent from authority = no trust on the center ⇒ rather, the center should be automated Fuss over what are really “features of the Internet itself” Which are not unique to blockchains, and blockchains cannot really provide them by themselves “Decentralization”, “consensus”, “zero downtime”, “secure”, “low-cost sharing”, . . . , etc. The worst is perhaps “consensus” Confusion between a casual everyday word and a computer science (CS) term What it really means is automatic replication of the same set of states (consensus in CS) “Matching intentions” can be represented by multi-signatures (consensus is expressed on the data after achieving an agreement elsewhere) Blockchain : What For? — 2020-06-25 – p.15/28
to people is like “explaining how vacuum tubes work to would-be YouTubers” Name of Technology Tele-vision Ledger Real Goal To transmit images to remote places To prove that records have not been altered (in order to freely spend money) First Technology Cathode-Ray Tube Blockchain First Model TV Bitcoin Evolved Into YouTube, Zoom, etc. ??? (Real applications) The first technology and first model become obsolete. . . Evolve so that the real goal (true value) can be pursued more freely Blockchain : What For? — 2020-06-25 – p.16/28
block_no : n block_no : n+1 block_no : n+2 block_no : n+3 block_no : n+1 block_no : n+2 block_no : n+3 block_no : n+4 Histroy with the largest cost to record or modify (history the most difficult to alter) is chosen Cryptographic digest of the previous block Transactions are digitally signed To create a block, its cryptographic digest needs to be below some certain number (Proof of Work) or one needs to win by voting weighted by the stakes in cryptocurrency (Proof of Stake) [both costly] Creator of a block can record the reward in cryptocurrency in the block, which is effective only when the block is included in the chosen history Means are provided to confirm existence of transactions validity existence uniqueness In proof of work, cast cost of electricity balances with market price of the cryptocurrency Proof is achieved by everyone following the recording system protected by cost of cryptocurrency Blockchain : What For? — 2020-06-25 – p.17/28
. . . (blockchain) Quorum, Hyperledger Besu, . . . (private blockchain) Hyperledger Fabric, Hyperledger Iroha, . . . (general-purpose private ledger) Hyperledger Indy, . . . (identifier management) Polkadot, . . . (second-layer and multiple-ledger interconnection) Corda, Hedera Hashgraph, BBc-1, . . . (some more alternatives) There are plenty But I believe that they should all be tested with “The Last Will Test” “Can you record a digital last will and testament in your blockchain?” After the death of the person, the private key used for the digital signature may no longer be a secret Can’t believe a notary saying ,“it is as signed before the death” (possible collusion with malicious heir) Blockchain : What For? — 2020-06-25 – p.18/28
SFUVSOMBOE 1VSDIBTF$POUSBDU -BOE"TTFU MBOE EFQPTJU USBOTGFSMBOESJHIUTUPCVZFS USBOTGFSQBZNFOUUPTFMMFS QBZNFOU EFQPTJU %JHJUBM5PLFO DSFBUFBOEpYJOUIFBJS FJUIFSDBOEPUIJT DSFBUFBOEpYJOUIFBJS DBOGSFFMZKPJOBOEMFBWF DBOGSFFMZKPJOBOEMFBWF 4FMMFS #VZFS JOUFSOBM TUBUF SFUVSONPOFZ TFUUMF USBOTGFS JOUFSOBM TUBUF USBOTGFS JOUFSOBM TUBUF 1. Purchase contract is fixed in the air to prevent taking away of land or money (both parties can verify the contract) 2. Deposit land rights and purchase money in the contract (if they change their minds, they can take them back) 3. When settled (anyone can do it if both right and money are deposited), the rights and money for the property are transferred simultaneously in one transaction Blockchain : What For? — 2020-06-25 – p.20/28
clone https://github.com/ks91/sample-smart-contracts.git Follow README 1. Setup a sample token project with brownie 2. Copy the content of contracts, scripts and tests directories of this sample project into the corresponding directories of the token project 3. Compile 4. Test I can demonstrate manually the test for automated escrow I wouldn’t today though Blockchain : What For? — 2020-06-25 – p.21/28
: //eg.beyond − blockchain.org/metauniv/? query string (important!) certificate = %3Cc%3E%3Cid . . . URL-encoded certificate (XML) & subtree = r − 7aa6334a311b357ed6 . . . Merkle subtree SAMPLE Since the URL is very long, we have shortened it to QR code, but . . . Expanded URL must be save for later proof (URL-shortening service may discontinue) Format of the graduation certificate is described later UTF-8/URL-encoded names and other information are listed as they are, but kept secret by HTTPS ⇒ Accessing to the above URL shows “Certificate is Verified!” and “The existence and the content of the following certificate is verified by matching the calculated Merkle root with the one stored in the Ethereum smart contract below.” What does it mean? BTW the certificate is real, but concealing the identity of the graduate (also the URL uses general verifier instead of one dedicated for Meta Univ.) Blockchain : What For? — 2020-06-25 – p.23/28
_digests; constructor () public { } function getStored(uint256 digest) public view returns (uint block_no) { return (_digests[digest]); } function isStored(uint256 digest) public view returns (bool isStored) { return (_digests[digest] > 0); } function store(uint256 digest) public returns (bool isAlreadyStored) { bool isRes = _digests[digest] > 0; if (!isRes) { _digests[digest] = block.number; } return (isRes); } } Save the block number at the time for the registered digest Blockchain : What For? — 2020-06-25 – p.24/28
stop or discontinue? ⇒ Even if it is stopped or discontinued, as long as there is a copy of the Ethereum blockchain somewhere in the world, you can read from it Can we renew or cancel a certificate? ⇒ BBc-1 library (bbc1-lib-registry) being used has a mechanism to update certificates Don’t you need a digital signature? ⇒ Good question! This time, handling key pairs would be cumbersome, so we omitted it, but BBc-1 allows “a signature by someone in a specific role” (in this case, president or university), or “verification of the signature by someone with the role at some point in the past” · Past digital signatures are generally difficult to verify, given possible leakage of private keys and obsolescence of technology, but BBc-1 presents a design that addresses and solves these challenges If it’s not digitally signed, can’t anyone forge it using the same mechanism? ⇒ Good question again! So we have published the Merkle root for Meta Univ. 2019 graduation : 93565db44ffeeb2945e97695265c0578ad2c9e75b958344cb5b8dfa9615d2bc6 (hexadecimal) Blockchain : What For? — 2020-06-25 – p.27/28
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