Using C#, I want to create an MD5 hash of a text file. How can I accomplish this?
Update: Thanks to everyone for their help. I've finally settled upon the following code -
// Create an MD5 hash digest of a file public string MD5HashFile(string fn) { byte[] hash = MD5.Create().ComputeHash(File.ReadAllBytes(fn)); return BitConverter.ToString(hash).Replace("-", ""); } Here's the routine I'm currently using.
using System.Security.Cryptography; public string HashFile(string filePath) { using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read)) { return HashFile(fs); } } public string HashFile( FileStream stream ) { StringBuilder sb = new StringBuilder(); if( stream != null ) { stream.Seek( 0, SeekOrigin.Begin ); MD5 md5 = MD5CryptoServiceProvider.Create(); byte[] hash = md5.ComputeHash( stream ); foreach( byte b in hash ) sb.Append( b.ToString( "x2" ) ); stream.Seek( 0, SeekOrigin.Begin ); } return sb.ToString(); } 
Short and to the point. filename is your text file's name:
using (var md5 = MD5.Create()) { return BitConverter.ToString(md5.ComputeHash(File.ReadAllBytes(filename))).Replace("-", ""); } This can be achieved by GetHashCode with overloads, allowing to pass either a filePath, a StreamReader or a Stream:
private static string GetHashCode(string filePath, HashAlgorithm cryptoService = null) => GetHashCode(fStream: new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite), cryptoService); private static string GetHashCode(StreamReader fileStreamReader, HashAlgorithm cryptoService = null) => GetHashCode(fileStreamReader.BaseStream, cryptoService); /// <summary> /// Compute hash code for file. /// </summary> /// <param name="fStream"></param> /// <param name="cryptoService">This can be either MD5, SHA1, SHA256, SHA384 or SHA512</param> /// <returns>Hash string</returns> private static string GetHashCode(Stream fStream, HashAlgorithm cryptoService = null) { // create or use the instance of the crypto service provider // this can be either MD5, SHA1, SHA256, SHA384 or SHA512 using (cryptoService ??= System.Security.Cryptography.SHA512.Create()) { using var tmpStream = fStream; var hash = cryptoService.ComputeHash(tmpStream); var hashString = Convert.ToBase64String(hash); return hashString.TrimEnd('='); } } // method Usage:
WriteLine("Default Sha512 Hash Code : {0}", GetHashCode(FilePath)); Or:
WriteLine("MD5 Hash Code : {0}", GetHashCode(FilePath, new MD5CryptoServiceProvider())); WriteLine("SHA1 Hash Code : {0}", GetHashCode(FilePath, new SHA1CryptoServiceProvider())); WriteLine("SHA256 Hash Code: {0}", GetHashCode(FilePath, new SHA256CryptoServiceProvider())); WriteLine("SHA384 Hash Code: {0}", GetHashCode(FilePath, new SHA384CryptoServiceProvider())); WriteLine("SHA512 Hash Code: {0}", GetHashCode(FilePath, new SHA512CryptoServiceProvider())); 
HashAlgorithm cryptoService = null and then add a default provider like so: using (cryptoService ??= System.Security.Cryptography.SHA512.Create()) - or if you prefer, you can use MD5 too (but I would not recommend it). This will simplify usage while keeping maximum flexibility (you are still able to add the provider of your choice).using var fileStream = fileStreamReader.BaseStream;.Here is a .NET Standard version that doesn't require reading the entire file into memory:
private byte[] CalculateMD5OfFile(FileInfo targetFile) { byte[] hashBytes = null; using (var hashcalc = System.Security.Cryptography.MD5.Create()) { using (FileStream inf = targetFile.OpenRead()) hashcalc.ComputeHash(inf); hashBytes = hashcalc.Hash; } return hashBytes; } You can convert the byte[] array into a string using the methods shown above. Also: You can change "MD5" in the third line to SHA1, SHA256, etc. to calculate other hashes.
