Metadata in the Blockchain: The OP_RETURN Explosion
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With the addition of OP_RETURN outputs in version 0.9, it became possible to attach arbitrary pieces of information to bitcoin transactions. This turns bitcoin into a low-level communications protocol, just like TCP/IP, on which many new applications can be built. Despite its powerful features, bitcoin is also limited, costly and inefficient compared to TCP/IP. After discussing which sorts of applications make this trade-off worthwhile, we talk about CoinSpark, a new open source protocol for enhancing bitcoin transactions, which makes extensive use of OP_RETURNs.
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Metadata in the Blockchain: The OP_RETURN Explosion
- 1. Metadata in the Blockchain: The OP_RETURN Explosion Coin Sciences Ltd http://coinspark.org/
- 2. If Bitcoin = Gold 2.0 then … What is the intrinsic value of a bitcoin? Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 3. What has gone wrong? (1) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 4. Early Internet growth Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ http://homes.cs.washington.edu/~lazowska/faculty.lecture/ innovation/hpcc/internet/hosts.html
- 5. What has gone wrong? (2) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 6. Gartner hype cycle Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 7. What has gone wrong? (3) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 3% (PayPal)
- 8. What is bitcoin for? Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 10. Bitcoin as communication Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 11. What can we send? Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ An expensive way to encode information
- 12. Fake addresses Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Permanent burden on unspent output list
- 13. Multisig addresses (1 of …) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Temporary burden on unspent output list
- 14. The OP_RETURN decision Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ https://bitcoinfoundation.org/2013/10/core-development-update-5/
- 15. OP_RETURNs Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Provably prunable, no unspent output
- 16. OP_RETURN size limit Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 17. OP_RETURNs vs TCP/IP OP_RETURNs TCP/IP Ratio Address space 2160 (collisions) 232 → 2128 1× Latency 5 seconds 1 second 5× Packet size 40 bytes 1.5 KB 36× Bandwidth ~100 bytes/s (50% of network!) 5 MB/s (50% of 100 Mbps) 50,000× Cost $850,000/GB (at $315/BTC) $0.10/GB 10,000,000× Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 18. So why use bitcoin?
- 19. Asynchronicity? Bitcoin TCP/IP Email Asynchronous Synchronous Asynchronous Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 20. Notarization Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Bitcoin TCP/IP Blockchain None
- 21. Message chaining Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Bitcoin TCP/IP Directed acyclic graph Request-response only
- 22. Privacy Bitcoin TCP/IP Addresses Pseudonymous but transaction chain analysis IP geolocation, traceable to individual via ISP Payloads Naked in public Private but seen by ISPs, switches Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 23. Payment model Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Bitcoin TCP/IP Per message, with message Subscription or pay- per-use, separate
- 24. So bitcoin is suitable for… • Tiny payload • High value – Hashes in general • Public broadcast • Permanently recorded • Non-instant • Pay-as-you-go Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 25. Financial transactions Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 26. Document notarization Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Bitproof, BlockSign, La Preuve, ProveBit, Proof of Existence, Stampd, Stampery
- 27. Historical records • Blog post about stuff in blockchain Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Lots more: http://www.righto.com/2014/02/ ascii-bernanke-wikileaks-photographs.html
- 28. Email with scarcity? Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 29. Universal family tree? • Show a family tree (DAG) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ http://recursivediscursion.blogspot.com/2011/04/gentle-introduction-to-graph-theory.html
- 30. 0 5 10 15 20 25xxxx 26xxxx 27xxxx 28xxxx 29xxxx 30xxxx 31xxxx 32xxxx 33xxxx 34xxxx 35xxxx 36xxxx 37xxxx Bitcoin block numbers (each column ~70 days) OP_RETURNs per block Bitcoin 0.9 released 19th March 2014 More at: coinsecrets.org Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 31. OP_RETURNs to block 375000 Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 27% 17% 9% 3%2% 2% 40% Open%Assets% Blockchain%ID% CoinSpark% Ascribe% Proof%of%Existence% Factom% Other%
- 32. CoinSpark
- 33. CoinSpark • Rich OP_RETURN protocol – Multiple metadata per OP_RETURN • Version 1.0 — September 2014 – Assets = lightweight scalable colored coins – Payment references • Version 2.0 — February 2015 – Transaction attachments / messaging • Version 3.0: simpler addressing, … Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 34. CoinSpark assets • Assets via OP_RETURN metadata – Not connected to bitcoin quantity • Genesis metadata: – Quantity, issuer transaction fees – Compressed web page URL – Hash of contract and key params • Transfer metadata: – Reference to genesis, quantity, outputs Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 35. CoinSpark assets for users • Lightweight wallet • Asset web page – View in browser – Hidden metadata – Domain authenticates issuer • Asset contract – Ready US + UK templates – Customizable Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 36. SparkBit wallet Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 37. Asset web page Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 38. Asset contract Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 39. Bitcoin transaction model Signed by Alice Alice 10.000 Bob 2.000 Alice 7.999 Miner 0.001 Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 40. CoinSpark asset model • Multiple assets per output – Low burden on network – No accidental loss • Default: all assets to last output • Metadata sends to other outputs – 40 bytes: up to 3 assets, unlimited outputs • Asset independence ⇒ scalability – Issuer provides tracking server for SPV Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 41. Example asset transaction Signed by Alice Alice 0.007 Bob 0.001 Alice 0.005 OP_RETURN Miner 0.001 A B C B A C B Output 1 Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 150 60 60 90
- 42. CoinSpark messages • Attach text and/or files to a bitcoin or CoinSpark asset transaction • Message discovery via OP_RETURN – Compressed URL / IP of delivery server – Outputs for which message intended – Hash of message + salt • Open source delivery server – Federated, non-centralized model Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 43. CoinSpark messages vs email • Hash proves message authenticity • Notarization of message on blockchain – Contracts, invoices, digital delivery • Also: public messages – Broadcast content + proof of existence • Future: message encryption – Requires public key, not just bitcoin address • Challenge: identity (Openname?) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 44. CoinSpark OP_RETURN format Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 53 50 4B CoinSpark marker (“SPK”) 61 FF — Last metadata opcode ···· Last metadata (until end of script) 01 60 Length of this metadata section— 61 FF — Metadata opcode ···· Metadata (up to 95 bytes) ＊
- 45. Metadata opcodes Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 61 7F — 67 72 74 80 EF — Reserved for CoinSpark Asset genesis (“g”) Payment reference (“r”) Asset transfer (“t”) Your application? 6D Message pointer (“m”)
- 46. Every byte is sacred Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 47. Every byte is sacred Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 48. Only encode surprises 000 = omit fields. If this is the first color transfer, assume input and output indices of 0. Otherwise take the indices from the previous color transfer. 001 = omit fields. If this is the first color transfer, assume input index 0 and output index 1. Otherwise take the indices from the previous color transfer and increment the output index only. 010 = omit fields. If this is the first color transfer, assume input index 1 and output index 0. Otherwise take the indices from the previous color transfer and increment the input index only. 011 = omit input index and use 1 byte for output index. If this is the first color transfer, assume input index 0. Otherwise use the same input index as the previous color transfer. 100 = omit output index and use 1 byte for input index. If this is the first color transfer, assume output index 0. Otherwise use the same output index as the previous color transfer. 101 = use 1 byte for input index, 1 byte for output index. 110 = use 1 byte for input index, 2 bytes for output index. 111 = use 2 bytes for input index, 2 bytes for output index. Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 49. Mantissa and exponent Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 625 trillion = 625×1012 ??11001001110001
- 50. Common domain strings www. .at .au .be .biz .br .ca .ch .cn .co.jp .co.kr .co.uk .co.za .co .com.ar .com.au .com.br .com.cn .com.mx .com.tr .com.tw .com.ua .com .cz .de .dk .edu .es .eu .fr .gov .gr .hk .hu .il .in .info .ir .it .jp .kr .me .mx .net .nl .no .org .pl .ps .ro .ru .se .sg .tr .tv .tw .ua .uk .us .vn Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 51. More domain name compression • 38 valid characters – 0 to 9, a to z, -‐ . • Two terminator characters ⇒ 40 – http:// vs https:// • 403 = 64000 < 65536 = 216 – So 3 characters per byte pair • Special case: IPv4 address – Obvious encoding in 4 bytes Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 52. Variable hash length ≥ 96 bits Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ 350,000,000 × 109 × 86400 × 365 × 7178 = 296
- 53. CoinSpark for Developers • Fully open source (MIT/AGPL) • Multilingual libraries – C/C++, Go, Java, JS, PHP, Python, Ruby • Fully decentralized – Server-side elements federated • Let’s do for bitcoin what the web did for TCP/IP Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 54. Back to the start… What is the intrinsic value of a bitcoin? Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 55. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 2011 2012 2013 2014 2015 2016 2017 2018 2019 Average block size (MB) Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ Current limit: 1 MB Economic prehistory Economic reality
- 56. What happens then? • Transactions compete for confirmation – Bidding via miner fee, paid only in bitcoin • Real price discovery – Econ 101: until supply = demand • If enough transactions (notarization?) are worth $10 to sender, all will cost that – No more cups of coffee! • Increasing block size limit just delays this Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 57. So: bitcoin = global bidding power for embedding data in the blockchain. Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 58. More from Coin Sciences
- 59. MultiChain • Private blockchain platform – Targeted at financial sector – Drop-in replacement for Bitcoin Core • Easy and quick deployment – Custom network parameters • Permission management • Native asset support • Stable alpha now available Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 60. Coin Secrets – coinsecrets.org Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/
- 61. php|python-OP_RETURN Coin Sciences Ltd Metadata in the Blockchain http://coinspark.org/ • Send OP_RETURN using Bitcoin Core – Doing it yourself is hard work! • Store and retrieve any data in blockchain – Uses OP_RETURNs in chained transactions – Returns reference like 356115-052075 for easy and fast retrieval • Use on command line or library – PHP and Python now, Ruby to come
- 62. Questions?