├── .gitignore ├── LICENSE ├── README.md ├── blockchain.go └── blockchain_test.go /.gitignore: -------------------------------------------------------------------------------- 1 | # Binaries for programs and plugins 2 | *.exe 3 | *.dll 4 | *.so 5 | *.dylib 6 | 7 | # Test binary, build with `go test -c` 8 | *.test 9 | 10 | # Output of the go coverage tool, specifically when used with LiteIDE 11 | *.out 12 | 13 | # Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736 14 | .glide/ 15 | 16 | .*.swp 17 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. Definitions. 8 | 9 | "License" shall mean the terms and conditions for use, reproduction, 10 | and distribution as defined by Sections 1 through 9 of this document. 11 | 12 | "Licensor" shall mean the copyright owner or entity authorized by 13 | the copyright owner that is granting the License. 14 | 15 | "Legal Entity" shall mean the union of the acting entity and all 16 | other entities that control, are controlled by, or are under common 17 | control with that entity. For the purposes of this definition, 18 | "control" means (i) the power, direct or indirect, to cause the 19 | direction or management of such entity, whether by contract or 20 | otherwise, or (ii) ownership of fifty percent (50%) or more of the 21 | outstanding shares, or (iii) beneficial ownership of such entity. 22 | 23 | "You" (or "Your") shall mean an individual or Legal Entity 24 | exercising permissions granted by this License. 25 | 26 | "Source" form shall mean the preferred form for making modifications, 27 | including but not limited to software source code, documentation 28 | source, and configuration files. 29 | 30 | "Object" form shall mean any form resulting from mechanical 31 | transformation or translation of a Source form, including but 32 | not limited to compiled object code, generated documentation, 33 | and conversions to other media types. 34 | 35 | "Work" shall mean the work of authorship, whether in Source or 36 | Object form, made available under the License, as indicated by a 37 | copyright notice that is included in or attached to the work 38 | (an example is provided in the Appendix below). 39 | 40 | "Derivative Works" shall mean any work, whether in Source or Object 41 | form, that is based on (or derived from) the Work and for which the 42 | editorial revisions, annotations, elaborations, or other modifications 43 | represent, as a whole, an original work of authorship. For the purposes 44 | of this License, Derivative Works shall not include works that remain 45 | separable from, or merely link (or bind by name) to the interfaces of, 46 | the Work and Derivative Works thereof. 47 | 48 | "Contribution" shall mean any work of authorship, including 49 | the original version of the Work and any modifications or additions 50 | to that Work or Derivative Works thereof, that is intentionally 51 | submitted to Licensor for inclusion in the Work by the copyright owner 52 | or by an individual or Legal Entity authorized to submit on behalf of 53 | the copyright owner. For the purposes of this definition, "submitted" 54 | means any form of electronic, verbal, or written communication sent 55 | to the Licensor or its representatives, including but not limited to 56 | communication on electronic mailing lists, source code control systems, 57 | and issue tracking systems that are managed by, or on behalf of, the 58 | Licensor for the purpose of discussing and improving the Work, but 59 | excluding communication that is conspicuously marked or otherwise 60 | designated in writing by the copyright owner as "Not a Contribution." 61 | 62 | "Contributor" shall mean Licensor and any individual or Legal Entity 63 | on behalf of whom a Contribution has been received by Licensor and 64 | subsequently incorporated within the Work. 65 | 66 | 2. Grant of Copyright License. Subject to the terms and conditions of 67 | this License, each Contributor hereby grants to You a perpetual, 68 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 69 | copyright license to reproduce, prepare Derivative Works of, 70 | publicly display, publicly perform, sublicense, and distribute the 71 | Work and such Derivative Works in Source or Object form. 72 | 73 | 3. Grant of Patent License. Subject to the terms and conditions of 74 | this License, each Contributor hereby grants to You a perpetual, 75 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 76 | (except as stated in this section) patent license to make, have made, 77 | use, offer to sell, sell, import, and otherwise transfer the Work, 78 | where such license applies only to those patent claims licensable 79 | by such Contributor that are necessarily infringed by their 80 | Contribution(s) alone or by combination of their Contribution(s) 81 | with the Work to which such Contribution(s) was submitted. If You 82 | institute patent litigation against any entity (including a 83 | cross-claim or counterclaim in a lawsuit) alleging that the Work 84 | or a Contribution incorporated within the Work constitutes direct 85 | or contributory patent infringement, then any patent licenses 86 | granted to You under this License for that Work shall terminate 87 | as of the date such litigation is filed. 88 | 89 | 4. Redistribution. You may reproduce and distribute copies of the 90 | Work or Derivative Works thereof in any medium, with or without 91 | modifications, and in Source or Object form, provided that You 92 | meet the following conditions: 93 | 94 | (a) You must give any other recipients of the Work or 95 | Derivative Works a copy of this License; and 96 | 97 | (b) You must cause any modified files to carry prominent notices 98 | stating that You changed the files; and 99 | 100 | (c) You must retain, in the Source form of any Derivative Works 101 | that You distribute, all copyright, patent, trademark, and 102 | attribution notices from the Source form of the Work, 103 | excluding those notices that do not pertain to any part of 104 | the Derivative Works; and 105 | 106 | (d) If the Work includes a "NOTICE" text file as part of its 107 | distribution, then any Derivative Works that You distribute must 108 | include a readable copy of the attribution notices contained 109 | within such NOTICE file, excluding those notices that do not 110 | pertain to any part of the Derivative Works, in at least one 111 | of the following places: within a NOTICE text file distributed 112 | as part of the Derivative Works; within the Source form or 113 | documentation, if provided along with the Derivative Works; or, 114 | within a display generated by the Derivative Works, if and 115 | wherever such third-party notices normally appear. The contents 116 | of the NOTICE file are for informational purposes only and 117 | do not modify the License. You may add Your own attribution 118 | notices within Derivative Works that You distribute, alongside 119 | or as an addendum to the NOTICE text from the Work, provided 120 | that such additional attribution notices cannot be construed 121 | as modifying the License. 122 | 123 | You may add Your own copyright statement to Your modifications and 124 | may provide additional or different license terms and conditions 125 | for use, reproduction, or distribution of Your modifications, or 126 | for any such Derivative Works as a whole, provided Your use, 127 | reproduction, and distribution of the Work otherwise complies with 128 | the conditions stated in this License. 129 | 130 | 5. Submission of Contributions. Unless You explicitly state otherwise, 131 | any Contribution intentionally submitted for inclusion in the Work 132 | by You to the Licensor shall be under the terms and conditions of 133 | this License, without any additional terms or conditions. 134 | Notwithstanding the above, nothing herein shall supersede or modify 135 | the terms of any separate license agreement you may have executed 136 | with Licensor regarding such Contributions. 137 | 138 | 6. Trademarks. This License does not grant permission to use the trade 139 | names, trademarks, service marks, or product names of the Licensor, 140 | except as required for reasonable and customary use in describing the 141 | origin of the Work and reproducing the content of the NOTICE file. 142 | 143 | 7. Disclaimer of Warranty. Unless required by applicable law or 144 | agreed to in writing, Licensor provides the Work (and each 145 | Contributor provides its Contributions) on an "AS IS" BASIS, 146 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 147 | implied, including, without limitation, any warranties or conditions 148 | of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A 149 | PARTICULAR PURPOSE. You are solely responsible for determining the 150 | appropriateness of using or redistributing the Work and assume any 151 | risks associated with Your exercise of permissions under this License. 152 | 153 | 8. Limitation of Liability. In no event and under no legal theory, 154 | whether in tort (including negligence), contract, or otherwise, 155 | unless required by applicable law (such as deliberate and grossly 156 | negligent acts) or agreed to in writing, shall any Contributor be 157 | liable to You for damages, including any direct, indirect, special, 158 | incidental, or consequential damages of any character arising as a 159 | result of this License or out of the use or inability to use the 160 | Work (including but not limited to damages for loss of goodwill, 161 | work stoppage, computer failure or malfunction, or any and all 162 | other commercial damages or losses), even if such Contributor 163 | has been advised of the possibility of such damages. 164 | 165 | 9. Accepting Warranty or Additional Liability. While redistributing 166 | the Work or Derivative Works thereof, You may choose to offer, 167 | and charge a fee for, acceptance of support, warranty, indemnity, 168 | or other liability obligations and/or rights consistent with this 169 | License. However, in accepting such obligations, You may act only 170 | on Your own behalf and on Your sole responsibility, not on behalf 171 | of any other Contributor, and only if You agree to indemnify, 172 | defend, and hold each Contributor harmless for any liability 173 | incurred by, or claims asserted against, such Contributor by reason 174 | of your accepting any such warranty or additional liability. 175 | 176 | END OF TERMS AND CONDITIONS 177 | 178 | APPENDIX: How to apply the Apache License to your work. 179 | 180 | To apply the Apache License to your work, attach the following 181 | boilerplate notice, with the fields enclosed by brackets "[]" 182 | replaced with your own identifying information. (Don't include 183 | the brackets!) The text should be enclosed in the appropriate 184 | comment syntax for the file format. We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright [yyyy] [name of copyright owner] 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Blockchain 2 | 3 | This repository implements a very simple Blockchain, loosely based off of this 4 | post and its sequel: https://medium.com/programmers-blockchain/create-simple-blockchain-java-tutorial-from-scratch-6eeed3cb03fa 5 | 6 | See the test file for basic usage. 7 | -------------------------------------------------------------------------------- /blockchain.go: -------------------------------------------------------------------------------- 1 | // Package blockchain implements a simple blockchain. 2 | package blockchain 3 | 4 | import ( 5 | "bytes" 6 | "container/list" 7 | "crypto/ecdsa" 8 | "crypto/elliptic" 9 | "crypto/rand" 10 | "crypto/sha256" 11 | "crypto/x509" 12 | "encoding/binary" 13 | "encoding/hex" 14 | "errors" 15 | "math/big" 16 | "strings" 17 | "time" 18 | ) 19 | 20 | // Blockchain represents the blockchain. 21 | type Blockchain struct { 22 | l *list.List 23 | difficulty int 24 | proofPrefix string 25 | } 26 | 27 | // New constructs a new Blockchain with the provided mining difficulty. 28 | func New(difficulty int) Blockchain { 29 | return Blockchain{ 30 | l: list.New(), 31 | difficulty: difficulty, 32 | proofPrefix: strings.Repeat("0", difficulty), 33 | } 34 | } 35 | 36 | // Add adds a new block to the chain, returning a reference to it. 37 | func (c Blockchain) NewBlock() *Block { 38 | const initialNonce = 0 39 | 40 | var prevHash []byte 41 | if prevBlock := c.l.Back(); prevBlock != nil { 42 | prevHash = prevBlock.Value.(*Block).Hash() 43 | } 44 | block := &Block{ 45 | prevHash: prevHash, 46 | timestamp: time.Now(), 47 | nonce: initialNonce, 48 | difficulty: c.difficulty, 49 | proofPrefix: c.proofPrefix, 50 | } 51 | c.l.PushBack(block) 52 | return block 53 | } 54 | 55 | // Len returns the length of the blockchain. 56 | func (c Blockchain) Len() int { 57 | return c.l.Len() 58 | } 59 | 60 | // WorkProven returns true if the provided hex-encoded hash counts as valid 61 | // proof-of-work. 62 | func (c Blockchain) WorkProven(hash string) bool { 63 | return strings.HasPrefix(hash, c.proofPrefix) 64 | } 65 | 66 | // Valid checks if this blockchain is valid. For a blockchain to be valid, 67 | // each block must have valid proof-of-work, and each previous hash reference 68 | // must match that of the previous block. 69 | func (c Blockchain) Valid() bool { 70 | for e := c.l.Front(); e != nil; e = e.Next() { 71 | currBlock := e.Value.(*Block) 72 | if !c.WorkProven(currBlock.HashString()) { 73 | return false 74 | } 75 | 76 | if prev := e.Prev(); prev != nil { 77 | prevBlock := prev.Value.(*Block) 78 | 79 | if !bytes.Equal(prevBlock.Hash(), currBlock.prevHash) { 80 | return false 81 | } 82 | } 83 | } 84 | 85 | return true 86 | } 87 | 88 | // ForEach calls f once with each block on the chain. 89 | func (c Blockchain) ForEach(f func(*Block)) { 90 | for e := c.l.Front(); e != nil; e = e.Next() { 91 | block := e.Value.(*Block) 92 | f(block) 93 | } 94 | } 95 | 96 | // Block represents a single piece of data in the blockchain. 97 | type Block struct { 98 | prevHash []byte 99 | timestamp time.Time 100 | nonce uint32 101 | transactions []Transaction 102 | difficulty int 103 | proofPrefix string 104 | } 105 | 106 | // String returns a readable version of this block, including all of its 107 | // transactions. 108 | func (b Block) String() string { 109 | const idSize = 6 110 | 111 | hashString := b.HashString() 112 | var buf bytes.Buffer 113 | buf.WriteString("block " + hashString + "\n") 114 | buf.WriteString(strings.Repeat("=", len("block "+hashString)) + "\n") 115 | for _, transaction := range b.transactions { 116 | from, to := transaction.Sender(), transaction.Receiver() 117 | shortFrom := from[:idSize] + "..." + from[len(from)-idSize:] 118 | shortTo := to[:idSize] + "..." + to[len(to)-idSize:] 119 | buf.WriteString(shortFrom + " -> " + shortTo + ": ") 120 | buf.Write(transaction.data) 121 | buf.WriteString("\n") 122 | } 123 | buf.WriteString("\n") 124 | return buf.String() 125 | } 126 | 127 | // SendTransaction sends a transaction from the identity "from" to the public 128 | // key "to". The transaction is automatically signed, returning an error if 129 | // signing fails. 130 | func (b *Block) SendTransaction(from Identity, to *ecdsa.PublicKey, data []byte) error { 131 | random := make([]byte, 4) 132 | if _, err := rand.Read(random); err != nil { 133 | return err 134 | } 135 | t := Transaction{ 136 | sender: &from.signer.PublicKey, 137 | receiver: to, 138 | data: data, 139 | random: random, 140 | } 141 | if err := t.Sign(from); err != nil { 142 | return errors.New("blockchain.SendTransaction: failed to sign transaction: " + err.Error()) 143 | } 144 | b.transactions = append(b.transactions, t) 145 | return nil 146 | } 147 | 148 | // Hash calculates the block's hash. It uses the previous block's hash along 149 | // with this block's timestamp, nonce, and data. 150 | func (b Block) Hash() []byte { 151 | v := make([]byte, 4) 152 | binary.LittleEndian.PutUint32(v, b.nonce) 153 | 154 | hasher := sha256.New() 155 | hasher.Write(b.prevHash) 156 | hasher.Write(mustBinary(b.timestamp.MarshalBinary())) 157 | hasher.Write(v) 158 | // NOTE: this part may need to be reworked, e.g. to use a merkle tree 159 | for _, t := range b.transactions { 160 | hasher.Write(t.Hash()) 161 | } 162 | return hasher.Sum(nil) 163 | } 164 | 165 | // HashString returns the hex-encoded result of Hash(). 166 | func (b Block) HashString() string { 167 | return hex.EncodeToString(b.Hash()) 168 | } 169 | 170 | // Timestamp returns the block's timestamp. 171 | func (b Block) Timestamp() time.Time { 172 | return b.timestamp 173 | } 174 | 175 | // Data returns the block's transactions. 176 | func (b Block) Transactions() []Transaction { 177 | return b.transactions 178 | } 179 | 180 | // Mine attempts to make this block valid by searching for a nonce value that 181 | // will qualify as proof-of-work. Once it succeeds, it returns the resulting 182 | // hex-encoded hash. 183 | func (b *Block) Mine() string { 184 | for !strings.HasPrefix(b.HashString(), b.proofPrefix) { 185 | b.nonce++ 186 | } 187 | return b.HashString() 188 | } 189 | 190 | // Identity represents a user of the blockchain. It's analogous to bitcoin's 191 | // wallet in that it is used to sign messages. 192 | type Identity struct { 193 | signer *ecdsa.PrivateKey 194 | } 195 | 196 | // NewIdentity constructs a new identity. In doing so it generates a new 197 | // private/public key pair. 198 | func NewIdentity() (Identity, error) { 199 | // No idea which elliptic curve is best here. 200 | privateKey, err := ecdsa.GenerateKey(elliptic.P224(), rand.Reader) 201 | if err != nil { 202 | return Identity{}, errors.New("blockchain.NewIdentity: " + err.Error()) 203 | } 204 | 205 | return Identity{ 206 | signer: privateKey, 207 | }, nil 208 | } 209 | 210 | // PublicKey returns the public key associated with this identity. 211 | func (i Identity) PublicKey() *ecdsa.PublicKey { 212 | return &i.signer.PublicKey 213 | } 214 | 215 | // Transaction represents a signed message on the blockchain. 216 | type Transaction struct { 217 | sender, receiver *ecdsa.PublicKey 218 | // random is a random sequence of bytes intended to reduce the chances of hash collisions 219 | data, random []byte 220 | sig1, sig2 *big.Int 221 | } 222 | 223 | // Hash returns this transaction's hash, which serves as an identifier. 224 | func (t Transaction) Hash() []byte { 225 | hasher := sha256.New() 226 | hasher.Write(mustBinary(x509.MarshalPKIXPublicKey(t.sender))) 227 | hasher.Write(mustBinary(x509.MarshalPKIXPublicKey(t.receiver))) 228 | hasher.Write(t.data) 229 | hasher.Write(t.random) 230 | return hasher.Sum(nil) 231 | } 232 | 233 | // Data returns the underlying data of this transaction. 234 | func (t Transaction) Data() []byte { 235 | return t.data 236 | } 237 | 238 | // Sender returns a hex-encoded version of the sender's public key. 239 | func (t Transaction) Sender() string { 240 | return hex.EncodeToString(mustBinary(x509.MarshalPKIXPublicKey(t.sender))) 241 | } 242 | 243 | // Receiver returns a hex-encoded version of the receiver's public key. 244 | func (t Transaction) Receiver() string { 245 | return hex.EncodeToString(mustBinary(x509.MarshalPKIXPublicKey(t.receiver))) 246 | } 247 | 248 | // Sign signs the transaction using the given identity. It must be equal to the 249 | // sender of the message, but for security reasons we don't want to save the 250 | // private key within the transaction itself. 251 | func (t *Transaction) Sign(identity Identity) error { 252 | if !bytes.Equal(mustBinary(x509.MarshalPKIXPublicKey(identity.PublicKey())), mustBinary(x509.MarshalPKIXPublicKey(t.sender))) { 253 | return errors.New("can't sign transaction unless you're the sender") 254 | } 255 | 256 | r, s, err := ecdsa.Sign(rand.Reader, identity.signer, t.Hash()) 257 | if err != nil { 258 | return errors.New("blockchain.Transaction.Sign: " + err.Error()) 259 | } 260 | t.sig1, t.sig2 = r, s 261 | return nil 262 | } 263 | 264 | // Signed returns true if the transaction was signed and could be verified, 265 | // otherwise false. 266 | func (t *Transaction) Signed() bool { 267 | if t.sig1 == nil || t.sig2 == nil { 268 | return false 269 | } 270 | return ecdsa.Verify(t.sender, t.Hash(), t.sig1, t.sig2) 271 | } 272 | 273 | func mustBinary(b []byte, err error) []byte { 274 | if err != nil { 275 | panic(err) 276 | } 277 | return b 278 | } 279 | -------------------------------------------------------------------------------- /blockchain_test.go: -------------------------------------------------------------------------------- 1 | package blockchain_test 2 | 3 | import ( 4 | "testing" 5 | 6 | blockchain "github.com/dradtke/go-blockchain" 7 | ) 8 | 9 | func TestBlockchain(t *testing.T) { 10 | const difficulty = 2 11 | 12 | chain := blockchain.New(difficulty) 13 | me, you := mustIdentity(blockchain.NewIdentity()), mustIdentity(blockchain.NewIdentity()) 14 | 15 | block := chain.NewBlock() 16 | if err := block.SendTransaction(me, you.PublicKey(), []byte("why hello there!")); err != nil { 17 | t.Fatalf("failed to send transaction: %s", err) 18 | } 19 | block.Mine() 20 | 21 | block = chain.NewBlock() 22 | if err := block.SendTransaction(you, me.PublicKey(), []byte("and hello to you too!")); err != nil { 23 | t.Fatalf("failed to send transaction: %s", err) 24 | } 25 | block.Mine() 26 | 27 | if !chain.Valid() { 28 | t.Error("blockchain is not valid") 29 | } 30 | 31 | chain.ForEach(func(block *blockchain.Block) { 32 | t.Log(block) 33 | }) 34 | } 35 | 36 | func TestEmptyBlockchain(t *testing.T) { 37 | const difficulty = 1 38 | chain := blockchain.New(difficulty) 39 | 40 | if !chain.Valid() { 41 | t.Error("an empty blockchain must be valid") 42 | } 43 | } 44 | 45 | func mustIdentity(identity blockchain.Identity, err error) blockchain.Identity { 46 | if err != nil { 47 | panic(err) 48 | } 49 | return identity 50 | } 51 | --------------------------------------------------------------------------------