Initial upload

tx_blockchain.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28729.10
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "tx_blockchain", "tx_blockchain\tx_blockchain.csproj", "{6AACD7A7-B242-4B60-8687-A3AE6F09596F}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{6AACD7A7-B242-4B60-8687-A3AE6F09596F}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6AACD7A7-B242-4B60-8687-A3AE6F09596F}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6AACD7A7-B242-4B60-8687-A3AE6F09596F}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6AACD7A7-B242-4B60-8687-A3AE6F09596F}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {EA8AC697-9C2A-4A34-AE6D-3407B0364D85}
+	EndGlobalSection
+EndGlobal

tx_blockchain/App_Start/RouteConfig.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web;
+using System.Web.Mvc;
+using System.Web.Routing;
+
+namespace tx_blockchain
+{
+    public class RouteConfig
+    {
+        public static void RegisterRoutes(RouteCollection routes)
+        {
+            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
+
+            routes.MapRoute(
+                name: "Default",
+                url: "{controller}/{action}/{id}",
+                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
+            );
+        }
+    }
+}

tx_blockchain/App_Start/WebApiConfig.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web.Http;
+
+namespace tx_blockchain
+{
+    public static class WebApiConfig
+    {
+        public static void Register(HttpConfiguration config)
+        {
+            // Web API configuration and services
+
+            // Web API routes
+            config.MapHttpAttributeRoutes();
+
+            config.Routes.MapHttpRoute(
+                name: "DefaultApi",
+                routeTemplate: "api/{controller}/{id}",
+                defaults: new { id = RouteParameter.Optional }
+            );
+        }
+    }
+}

tx_blockchain/Blockchain/Block.cs

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+using System;
+using System.Security.Cryptography;
+using System.Text;
+
+// this class contains the structure of a single block in the
+// blockchain and stores the document MD5 hash in the data property.
+public class Block
+{
+    public int Index { get; set; }
+    public DateTime TimeStamp { get; set; }
+    public string PreviousBlockHash { get; set; }
+    public string BlockHash { get; set; }
+    public string Data { get; set; }
+    public int Nonce { get; set; } = 0;
+
+    // constructor
+    public Block (DateTime timeStamp, string previousBlockHash, string data)
+    {
+        Index = 0;
+        TimeStamp = timeStamp;
+        PreviousBlockHash = previousBlockHash;
+        Data = data;
+        BlockHash = GenerateBlockHash();
+    }
+
+    // generates a new hash for the block including the time stamp,
+    // the previous block has, the data and the nonce.
+    internal string GenerateBlockHash()
+    {
+        SHA256 sha256 = SHA256.Create();
+
+        byte[] bInput = Encoding.ASCII.GetBytes($"{TimeStamp}-{PreviousBlockHash ?? ""}-{Data}-{Nonce}");
+        byte[] bOutput = sha256.ComputeHash(bInput);
+
+        return Convert.ToBase64String(bOutput);
+    }
+
+    // this method is generating hashes until a new hash with a specific
+    // number of leading zeros is created
+    public void Mine(int difficulty)
+    {
+        string sLeadingZeros = new string('0', difficulty);
+
+        while (this.BlockHash == null || this.BlockHash.Substring(0, difficulty) != sLeadingZeros)
+        {
+            this.Nonce++;
+            this.BlockHash = this.GenerateBlockHash();
+        }
+    }
+}

tx_blockchain/Blockchain/Blockchain.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web;
+
+// this class implements the actual linked list
+public class Blockchain
+{
+    public IList<Block> Chain { set; get; }
+    public int Difficulty { set; get; } = 2;
+
+    public Blockchain()
+    {
+        InitializeChain();
+    }
+
+    public Blockchain(bool newBlockChain)
+    {
+        InitializeChain();
+        AddGenesisBlock(); // add the first block
+    }
+
+    public void InitializeChain()
+    {
+        Chain = new List<Block>();
+    }
+
+    public Block CreateGenesisBlock()
+    {
+        return new Block(DateTime.Now, null, "{}");
+    }
+
+    public void AddGenesisBlock()
+    {
+        Chain.Add(CreateGenesisBlock());
+    }
+
+    // return the last block in the list
+    public Block GetCurrentBlock()
+    {
+        return Chain[Chain.Count - 1];
+    }
+
+    // adds a new block to the chain
+    public void AddBlock(Block block)
+    {
+        // check blockchain consistency first
+        if (this.IsValid() == true) 
+        {
+            Block latestBlock = GetCurrentBlock();
+            block.Index = latestBlock.Index + 1;
+            block.PreviousBlockHash = latestBlock.BlockHash;
+
+            // mine for a valid hash
+            block.Mine(this.Difficulty);
+
+            // add the block to the chain
+            Chain.Add(block);
+        }
+    }
+
+    // checks, if the blockchain is consistent by
+    // re-generating and comparing the hashes in each block
+    public bool IsValid()
+    {
+        for (int i = 1; i < Chain.Count; i++)
+        {
+            Block currentBlock = Chain[i];
+            Block previousBlock = Chain[i - 1];
+
+            if (currentBlock.BlockHash != currentBlock.GenerateBlockHash())
+            {
+                return false;
+            }
+
+            if (currentBlock.PreviousBlockHash != previousBlock.BlockHash)
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}

tx_blockchain/CSS/site.css

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+.viewer {
+    height: calc(100vh - 56px);
+}
+
+.verified::before {
+    font-size: 100px;
+    font-family: "Font Awesome 5 Free";
+    font-weight: 900;
+    content: "\f058";
+}
+
+.notverified::before {
+    font-size: 100px;
+    font-family: "Font Awesome 5 Free";
+    font-weight: 900;
+    content: "\f057";
+}
+
+.result {
+    display: block;
+}
+
+.verified {
+    color: green; 
+}
+
+.notverified {
+    color: red;
+}
+
+.result-text-notverified::before {
+    content: "The document could not be validated with the last block on the blockchain.";
+}
+
+.result-text-verified::before {
+    content: "The document has been validated with the last block on the blockchain.";
+}
+
+#tx-documentViewer {
+    top: 56px !important;
+    height: calc(100vH - 56px) !important;
+}

tx_blockchain/ClassDiagram1.cd

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+<?xml version="1.0" encoding="utf-8"?>
+<ClassDiagram /> 

tx_blockchain/Controllers/DocumentController.cs

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+using Newtonsoft.Json;
+using System;
+using System.Web.Http;
+using System.Web.Mvc;
+using tx_blockchain.Helpers;
+using tx_blockchain.Models;
+
+namespace tx_blockchain.Controllers
+{
+    public class DocumentController : Controller
+    {
+        // this method stores the document hash in the blockchain
+        [System.Web.Http.HttpPost]
+        public ActionResult StoreDocument(
+            [FromBody] string Document,
+            [FromBody] string UniqueId,
+            [FromBody] string SignerName)
+        {
+            byte[] bPDF;
+
+            // create temporary ServerTextControl
+            using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
+            {
+                tx.Create();
+
+                // load the document
+                tx.Load(Convert.FromBase64String(Document),
+                    TXTextControl.BinaryStreamType.InternalUnicodeFormat);
+
+                TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings()
+                {
+                    CreatorApplication = "TX Text Control Sample Application",
+                };
+
+                // save the document as PDF
+                tx.Save(out bPDF, TXTextControl.BinaryStreamType.AdobePDF, saveSettings);
+            }
+
+            // calculate the MD5 checksum of the binary data
+            // and store in SignedDocument object
+            SignedDocument document = new SignedDocument()
+            {
+                Checksum = Checksum.CalculateMD5(bPDF)
+            };
+
+            // define a Blockchain object
+            Blockchain bcDocument;
+
+            // if the blockchain exists, load it
+            if (System.IO.File.Exists(
+                Server.MapPath("~/App_Data/Blockchains/" + UniqueId + ".bc")))
+            {
+                string bc = System.IO.File.ReadAllText(
+                    Server.MapPath("~/App_Data/Blockchains/" + UniqueId + ".bc"));
+
+                bcDocument = JsonConvert.DeserializeObject<Blockchain>(bc);
+            }
+            else
+                bcDocument = new Blockchain(true); // otherwise create a new blockchain
+
+            // add a new block to the blockchain and store the SignedDocument object
+            bcDocument.AddBlock(new Block(DateTime.Now, null, JsonConvert.SerializeObject(document)));
+
+            // store the blockchain as a file
+            System.IO.File.WriteAllText(
+                Server.MapPath("~/App_Data/Blockchains/" + UniqueId + ".bc"),
+                JsonConvert.SerializeObject(bcDocument));
+
+            // create and return a view model with the PDF and the unique document ID
+            StoredDocument storedDocument = new StoredDocument()
+            {
+                PDF = Convert.ToBase64String(bPDF),
+                DocumentId = UniqueId
+            };
+
+            return new JsonResult() { Data = storedDocument,
+                JsonRequestBehavior = JsonRequestBehavior.AllowGet };
+        }
+
+        // this method validates a document with the last block on the blockchain
+        [System.Web.Http.HttpPost]
+        public bool ValidateDocument([FromBody] string Document, [FromBody] string UniqueId)
+        {
+            if (Document == null || UniqueId == null)
+                return false;
+
+            // calculate the MD5 of the uploaded document
+            string sChecksum = Checksum.CalculateMD5(Convert.FromBase64String(Document));
+
+            Blockchain newDocument;
+
+            // load the associated blockchain
+            if (System.IO.File.Exists(
+                Server.MapPath("~/App_Data/Blockchains/" + UniqueId + ".bc")))
+            {
+                string bc = System.IO.File.ReadAllText(
+                    Server.MapPath("~/App_Data/Blockchains/" + UniqueId + ".bc"));
+
+                newDocument = JsonConvert.DeserializeObject<Blockchain>(bc);
+
+                // get the SignedDocument object from the block
+                SignedDocument signedDocument = 
+                    JsonConvert.DeserializeObject<SignedDocument>(newDocument.GetCurrentBlock().Data);
+
+                // compare the checksum in the stored block
+                // with the checksum of the uploaded document
+                if (signedDocument.Checksum == sChecksum)
+                    return true; // document valid
+                else
+                    return false; // not valid
+            }
+            else
+                return false; // blockchain doesn't exist
+        }
+    }
+}