Table of Contents
182 Executive Summary ..................................................................................................... iv
183 1 Introduction ............................................................................................................ 9
184 1.1 Background and History.................................................................................. 9
185 1.2 Purpose and Scope ...................................................................................... 10
186 1.3 Notes on Terms ............................................................................................ 10
187 1.4 Document Structure...................................................................................... 10
188 2 Blockchain Architecture...................................................................................... 12
189 2.1 Hashes.......................................................................................................... 12
190 2.2 Transactions ................................................................................................. 13
191 2.3 Asymmetric-Key Cryptography ..................................................................... 13
192 2.4 Addresses and Address Derivation............................................................... 14
193 2.4.1 Private Key Storage............................................................................ 14
194 2.5 Ledgers......................................................................................................... 15
195 2.6 Blocks ........................................................................................................... 19
196 2.7 Chaining Blocks ............................................................................................ 23
197 3 Blockchains in Operation.................................................................................... 23
198 4 Consensus............................................................................................................ 26
199 4.1 Proof of Work Consensus Model .................................................................. 26
200 4.2 Proof of Stake Consensus Model ................................................................. 29
201 4.3 Round Robin Consensus Model ................................................................... 30
202 4.4 Ledger Conflicts and Resolutions ................................................................. 30
203 5 Forking.................................................................................................................. 33
204 5.1 Soft Forks ..................................................................................................... 33
205 5.2 Hard Forks .................................................................................................... 33
206 5.3 Cryptographic Changes and Forks ............................................................... 34
207 6 Smart Contracts ................................................................................................... 35
208 7 Blockchain Categorization .................................................................................. 36
209 7.1 Permissioned ................................................................................................ 36
210 7.1.1 Application Considerations for Permissioned Blockchains ................. 36
211 7.1.2 Use Case Examples........................................................................... 37
212 7.2 Permissionless.............................................................................................. 38
213 7.2.1 Application Considerations for Permissionless Blockchains............... 38
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214 7.2.2 Use Case Examples........................................................................... 38
215 8 Blockchain Platforms .......................................................................................... 40
216 8.1 Cryptocurrencies........................................................................................... 40
217 8.1.1 Bitcoin (BTC) ...................................................................................... 40
218 8.1.2 Bitcoin Cash (BCC) ............................................................................ 41
219 8.1.3 Litecoin (LTC)..................................................................................... 41
220 8.1.4 Ethereum (ETH) ................................................................................. 41
221 8.1.5 Ethereum Classic (ETC)..................................................................... 41
222 8.1.6 Dash (DASH)...................................................................................... 42
223 8.1.7 Ripple (XRP) ...................................................................................... 42
224 8.2 Hyperledger .................................................................................................. 42
225 8.2.1 Hyperledger Fabric............................................................................. 42
226 8.2.2 Hyperledger Sawtooth........................................................................ 43
227 8.2.3 Hyperledger Iroha............................................................................... 43
228 8.2.4 Hyperledger Burrow............................................................................ 43
229 8.2.5 Hyperledger Indy ................................................................................ 43
230 8.3 MultiChain..................................................................................................... 43
231 9 Blockchain Limitations and Misconceptions..................................................... 44
232 9.1 Blockchain Control ........................................................................................ 44
233 9.2 Malicious Users............................................................................................. 44
234 9.3 No Trust ........................................................................................................ 45
235 9.4 Resource Usage ........................................................................................... 45
236 9.5 Transfer of Burden of Credential Storage to Users....................................... 46
237 9.6 Private/Public Key Infrastructure and Identity ............................................... 46
238 10 Conclusions.......................................................................................................... 47
239
240 List of Appendices
241 Appendix A— Acronyms ............................................................................................ 48
242 Appendix B— Glossary .............................................................................................. 50
243 Appendix C— References .......................................................................................... 55
244
245 List of Tables and Figures
246 Table 1: Examples of Inputs and SHA-256 Digest Values ............................................ 12
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247 Table 2: Example Transaction....................................................................................... 13
248 Figure 1 - A simple network maintaining a copy of a ledger across nodes.................... 16
249 Figure 2 - Submitting a Transaction to a Node, waiting in the Pending Transaction List
250 ............................................................................................................................... 17
251 Figure 3 - Transaction 4 information transmitted from node to node............................. 18
252 Figure 4 - Transaction 4 has been included into a block, nodes are transmitting the
253 information; the final node has not yet received the latest information................... 19
254 Figure 5: Example of a Merkle Tree .............................................................................. 21
255 Figure 6: Blockchain with Merkle Tree .......................................................................... 22
256 Figure 7: Generic Chain of Blocks................................................................................. 23
257 Figure 8: Transaction Being Added to Unspent Transaction Pool................................. 24
258 Figure 9: Finalized Block (Generalized) ........................................................................ 25
259 Figure 10: Distributed Network in Conflict ..................................................................... 31
260 Figure 11: Blockchains in Conflict ................................................................................. 31
261 Figure 12: Chain B Adds the Next Block ....................................................................... 32
262 Table 3: Impact of Quantum Computing on Common Cryptographic Algorithms .......... 34
263