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How To: Hash Data with Salt (C#/VB.NET) The code below demonstrates how to hash data and verify hashes. It supports MD5, SHA-1, SHA-256, SHA-384, and SHA-512 hashing algorithms. To help reduce the risk of dictionary attacks, the code appends random bytes (so-called "salt") to the original plain text before generating hashes. Please keep in mind that salt can only help against prebuilt dictionaries. If an intruder gets access to your system and uses a brute force attack, salt will not provide much value. Code samples are provided in C# and Visual Basic.NET. IMPORTANT: DATA HASHES CANNOT BE "DECRYPTED" BACK TO PLAIN TEXT. Notes
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C# code [printer-friendly version] [code output]/////////////////////////////////////////////////////////////////////////////// // SAMPLE: Hashing data with salt using MD5 and several SHA algorithms. // // To run this sample, create a new Visual C# project using the Console // Application template and replace the contents of the Class1.cs file with // the code below. // // THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, // EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED // WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE. // // Copyright (C) 2002 Obviex(TM). All rights reserved. // using System; using System.Text; using System.Security.Cryptography; /// <summary> /// This class generates and compares hashes using MD5, SHA1, SHA256, SHA384, /// and SHA512 hashing algorithms. Before computing a hash, it appends a /// randomly generated salt to the plain text, and stores this salt appended /// to the result. To verify another plain text value against the given hash, /// this class will retrieve the salt value from the hash string and use it /// when computing a new hash of the plain text. Appending a salt value to /// the hash may not be the most efficient approach, so when using hashes in /// a real-life application, you may choose to store them separately. You may /// also opt to keep results as byte arrays instead of converting them into /// base64-encoded strings. /// </summary> public class SimpleHash { /// <summary> /// Generates a hash for the given plain text value and returns a /// base64-encoded result. Before the hash is computed, a random salt /// is generated and appended to the plain text. This salt is stored at /// the end of the hash value, so it can be used later for hash /// verification. /// </summary> /// <param name="plainText"> /// Plaintext value to be hashed. The function does not check whether /// this parameter is null. /// </param> /// <param name="hashAlgorithm"> /// Name of the hash algorithm. Allowed values are: "MD5", "SHA1", /// "SHA256", "SHA384", and "SHA512" (if any other value is specified /// MD5 hashing algorithm will be used). This value is case-insensitive. /// </param> /// <param name="saltBytes"> /// Salt bytes. This parameter can be null, in which case a random salt /// value will be generated. /// </param> /// <returns> /// Hash value formatted as a base64-encoded string. /// </returns> public static string ComputeHash(string plainText, string hashAlgorithm, byte[] saltBytes) { // If salt is not specified, generate it on the fly. if (saltBytes == null) { // Define min and max salt sizes. int minSaltSize = 4; int maxSaltSize = 8; // Generate a random number for the size of the salt. Random random = new Random(); int saltSize = random.Next(minSaltSize, maxSaltSize); // Allocate a byte array, which will hold the salt. saltBytes = new byte[saltSize]; // Initialize a random number generator. RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); // Fill the salt with cryptographically strong byte values. rng.GetNonZeroBytes(saltBytes); } // Convert plain text into a byte array. byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText); // Allocate array, which will hold plain text and salt. byte[] plainTextWithSaltBytes = new byte[plainTextBytes.Length + saltBytes.Length]; // Copy plain text bytes into resulting array. for (int i=0; i < plainTextBytes.Length; i++) plainTextWithSaltBytes[i] = plainTextBytes[i]; // Append salt bytes to the resulting array. for (int i=0; i < saltBytes.Length; i++) plainTextWithSaltBytes[plainTextBytes.Length + i] = saltBytes[i]; // Because we support multiple hashing algorithms, we must define // hash object as a common (abstract) base class. We will specify the // actual hashing algorithm class later during object creation. HashAlgorithm hash; // Make sure hashing algorithm name is specified. if (hashAlgorithm == null) hashAlgorithm = ""; // Initialize appropriate hashing algorithm class. switch (hashAlgorithm.ToUpper()) { case "SHA1": hash = new SHA1Managed(); break; case "SHA256": hash = new SHA256Managed(); break; case "SHA384": hash = new SHA384Managed(); break; case "SHA512": hash = new SHA512Managed(); break; default: hash = new MD5CryptoServiceProvider(); break; } // Compute hash value of our plain text with appended salt. byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes); // Create array which will hold hash and original salt bytes. byte[] hashWithSaltBytes = new byte[hashBytes.Length + saltBytes.Length]; // Copy hash bytes into resulting array. for (int i=0; i < hashBytes.Length; i++) hashWithSaltBytes[i] = hashBytes[i]; // Append salt bytes to the result. for (int i=0; i < saltBytes.Length; i++) hashWithSaltBytes[hashBytes.Length + i] = saltBytes[i]; // Convert result into a base64-encoded string. string hashValue = Convert.ToBase64String(hashWithSaltBytes); // Return the result. return hashValue; } /// <summary> /// Compares a hash of the specified plain text value to a given hash /// value. Plain text is hashed with the same salt value as the original /// hash. /// </summary> /// <param name="plainText"> /// Plain text to be verified against the specified hash. The function /// does not check whether this parameter is null. /// </param> /// <param name="hashAlgorithm"> /// Name of the hash algorithm. Allowed values are: "MD5", "SHA1", /// "SHA256", "SHA384", and "SHA512" (if any other value is specified, /// MD5 hashing algorithm will be used). This value is case-insensitive. /// </param> /// <param name="hashValue"> /// Base64-encoded hash value produced by ComputeHash function. This value /// includes the original salt appended to it. /// </param> /// <returns> /// If computed hash mathes the specified hash the function the return /// value is true; otherwise, the function returns false. /// </returns> public static bool VerifyHash(string plainText, string hashAlgorithm, string hashValue) { // Convert base64-encoded hash value into a byte array. byte[] hashWithSaltBytes = Convert.FromBase64String(hashValue); // We must know size of hash (without salt). int hashSizeInBits, hashSizeInBytes; // Make sure that hashing algorithm name is specified. if (hashAlgorithm == null) hashAlgorithm = ""; // Size of hash is based on the specified algorithm. switch (hashAlgorithm.ToUpper()) { case "SHA1": hashSizeInBits = 160; break; case "SHA256": hashSizeInBits = 256; break; case "SHA384": hashSizeInBits = 384; break; case "SHA512": hashSizeInBits = 512; break; default: // Must be MD5 hashSizeInBits = 128; break; } // Convert size of hash from bits to bytes. hashSizeInBytes = hashSizeInBits / 8; // Make sure that the specified hash value is long enough. if (hashWithSaltBytes.Length < hashSizeInBytes) return false; // Allocate array to hold original salt bytes retrieved from hash. byte[] saltBytes = new byte[hashWithSaltBytes.Length - hashSizeInBytes]; // Copy salt from the end of the hash to the new array. for (int i=0; i < saltBytes.Length; i++) saltBytes[i] = hashWithSaltBytes[hashSizeInBytes + i]; // Compute a new hash string. string expectedHashString = ComputeHash(plainText, hashAlgorithm, saltBytes); // If the computed hash matches the specified hash, // the plain text value must be correct. return (hashValue == expectedHashString); } } /// <summary> /// Illustrates the use of the SimpleHash class. /// </summary> public class SimpleHashTest { /// <summary> /// The main entry point for the application. /// </summary> [STAThread] static void Main(string[] args) { string password = "myP@5sw0rd"; // original password string wrongPassword = "password"; // wrong password string passwordHashMD5 = SimpleHash.ComputeHash(password, "MD5", null); string passwordHashSha1 = SimpleHash.ComputeHash(password, "SHA1", null); string passwordHashSha256 = SimpleHash.ComputeHash(password, "SHA256", null); string passwordHashSha384 = SimpleHash.ComputeHash(password, "SHA384", null); string passwordHashSha512 = SimpleHash.ComputeHash(password, "SHA512", null); Console.WriteLine("COMPUTING HASH VALUES\r\n"); Console.WriteLine("MD5 : {0}", passwordHashMD5); Console.WriteLine("SHA1 : {0}", passwordHashSha1); Console.WriteLine("SHA256: {0}", passwordHashSha256); Console.WriteLine("SHA384: {0}", passwordHashSha384); Console.WriteLine("SHA512: {0}", passwordHashSha512); Console.WriteLine(""); Console.WriteLine("COMPARING PASSWORD HASHES\r\n"); Console.WriteLine("MD5 (good): {0}", SimpleHash.VerifyHash( password, "MD5", passwordHashMD5).ToString()); Console.WriteLine("MD5 (bad) : {0}", SimpleHash.VerifyHash( wrongPassword, "MD5", passwordHashMD5).ToString()); Console.WriteLine("SHA1 (good): {0}", SimpleHash.VerifyHash( password, "SHA1", passwordHashSha1).ToString()); Console.WriteLine("SHA1 (bad) : {0}", SimpleHash.VerifyHash( wrongPassword, "SHA1", passwordHashSha1).ToString()); Console.WriteLine("SHA256 (good): {0}", SimpleHash.VerifyHash( password, "SHA256", passwordHashSha256).ToString()); Console.WriteLine("SHA256 (bad) : {0}", SimpleHash.VerifyHash( wrongPassword, "SHA256", passwordHashSha256).ToString()); Console.WriteLine("SHA384 (good): {0}", SimpleHash.VerifyHash( password, "SHA384", passwordHashSha384).ToString()); Console.WriteLine("SHA384 (bad) : {0}", SimpleHash.VerifyHash( wrongPassword, "SHA384", passwordHashSha384).ToString()); Console.WriteLine("SHA512 (good): {0}", SimpleHash.VerifyHash( password, "SHA512", passwordHashSha512).ToString()); Console.WriteLine("SHA512 (bad) : {0}", SimpleHash.VerifyHash( wrongPassword, "SHA512", passwordHashSha512).ToString()); } } // // END OF FILE /////////////////////////////////////////////////////////////////////////////// VB.NET code [printer-friendly version] [code output]''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' SAMPLE: Hashing data with salt using MD5 and several SHA algorithms. ' ' To run this sample, create a new Visual Basic.NET project using the Console ' Application template and replace the contents of the Module1.vb file with ' the code below. ' ' THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, ' EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED ' WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE. ' ' Copyright (C) 2002 Obviex(TM). All rights reserved. ' Imports System Imports System.Text Imports System.Security.Cryptography Module Module1 ' <summary> ' This class generates and compares hashes using MD5, SHA1, SHA256, SHA384, ' and SHA512 hashing algorithms. Before computing a hash, it appends a ' randomly generated salt to the plain text, and stores this salt appended ' to the result. To verify another plain text value against the given hash, ' this class will retrieve the salt value from the hash string and use it ' when computing a new hash of the plain text. Appending a salt value to ' the hash may not be the most efficient approach, so when using hashes in ' a real-life application, you may choose to store them separately. You may ' also opt to keep results as byte arrays instead of converting them into ' base64-encoded strings. ' </summary> Public Class SimpleHash ' <summary> ' Generates a hash for the given plain text value and returns a ' base64-encoded result. Before the hash is computed, a random salt ' is generated and appended to the plain text. This salt is stored at ' the end of the hash value, so it can be used later for hash ' verification. ' </summary> ' <param name="plainText"> ' Plaintext value to be hashed. The function does not check whether ' this parameter is null. ' </param> ' < name="hashAlgorithm"> ' Name of the hash algorithm. Allowed values are: "MD5", "SHA1", ' "SHA256", "SHA384", and "SHA512" (if any other value is specified ' MD5 hashing algorithm will be used). This value is case-insensitive. ' </param> ' < name="saltBytes"> ' Salt bytes. This parameter can be null, in which case a random salt ' value will be generated. ' </param> ' <returns> ' Hash value formatted as a base64-encoded string. ' </returns> Public Shared Function ComputeHash(ByVal plainText As String, _ ByVal hashAlgorithm As String, _ ByVal saltBytes() As Byte) _ As String ' If salt is not specified, generate it on the fly. If (saltBytes Is Nothing) Then ' Define min and max salt sizes. Dim minSaltSize As Integer Dim maxSaltSize As Integer minSaltSize = 4 maxSaltSize = 8 ' Generate a random number for the size of the salt. Dim random As Random random = New Random() Dim saltSize As Integer saltSize = random.Next(minSaltSize, maxSaltSize) ' Allocate a byte array, which will hold the salt. saltBytes = New Byte(saltSize - 1){} ' Initialize a random number generator. Dim rng As RNGCryptoServiceProvider rng = New RNGCryptoServiceProvider() ' Fill the salt with cryptographically strong byte values. rng.GetNonZeroBytes(saltBytes) End If ' Convert plain text into a byte array. Dim plainTextBytes As Byte() plainTextBytes = Encoding.UTF8.GetBytes(plainText) ' Allocate array, which will hold plain text and salt. Dim plainTextWithSaltBytes() As Byte = _ New Byte(plainTextBytes.Length + saltBytes.Length - 1){} ' Copy plain text bytes into resulting array. Dim I As Integer For I = 0 To plainTextBytes.Length - 1 plainTextWithSaltBytes(I) = plainTextBytes(I) Next I ' Append salt bytes to the resulting array. For I = 0 To saltBytes.Length - 1 plainTextWithSaltBytes(plainTextBytes.Length + I) = saltBytes(I) Next I ' Because we support multiple hashing algorithms, we must define ' hash object as a common (abstract) base class. We will specify the ' actual hashing algorithm class later during object creation. Dim hash As HashAlgorithm ' Make sure hashing algorithm name is specified. If (hashAlgorithm Is Nothing) Then hashAlgorithm = "" End If ' Initialize appropriate hashing algorithm class. Select hashAlgorithm.ToUpper() Case "SHA1" hash = New SHA1Managed() Case "SHA256" hash = New SHA256Managed() Case "SHA384" hash = New SHA384Managed() Case "SHA512" hash = New SHA512Managed() Case Else hash = New MD5CryptoServiceProvider() End Select ' Compute hash value of our plain text with appended salt. Dim hashBytes As Byte() hashBytes = hash.ComputeHash(plainTextWithSaltBytes) ' Create array which will hold hash and original salt bytes. Dim hashWithSaltBytes() As Byte = _ New Byte(hashBytes.Length + _ saltBytes.Length - 1) {} ' Copy hash bytes into resulting array. For I = 0 To hashBytes.Length - 1 hashWithSaltBytes(I) = hashBytes(I) Next I ' Append salt bytes to the result. For I = 0 To saltBytes.Length - 1 hashWithSaltBytes(hashBytes.Length + I) = saltBytes(I) Next I ' Convert result into a base64-encoded string. Dim hashValue As String hashValue = Convert.ToBase64String(hashWithSaltBytes) ' Return the result. ComputeHash = hashValue End Function ' <summary> ' Compares a hash of the specified plain text value to a given hash ' value. Plain text is hashed with the same salt value as the original ' hash. ' </summary> ' <param name="plainText"> ' Plain text to be verified against the specified hash. The function ' does not check whether this parameter is null. ' </param> ' < name="hashAlgorithm"> ' Name of the hash algorithm. Allowed values are: "MD5", "SHA1", ' "SHA256", "SHA384", and "SHA512" (if any other value is specified ' MD5 hashing algorithm will be used). This value is case-insensitive. ' </param> ' < name="hashValue"> ' Base64-encoded hash value produced by ComputeHash function. This value ' includes the original salt appended to it. ' </param> ' <returns> ' If computed hash mathes the specified hash the function the return ' value is true; otherwise, the function returns false. ' </returns> Public Shared Function VerifyHash(ByVal plainText As String, _ ByVal hashAlgorithm As String, _ ByVal hashValue As String) _ As Boolean ' Convert base64-encoded hash value into a byte array. Dim hashWithSaltBytes As Byte() hashWithSaltBytes = Convert.FromBase64String(hashValue) ' We must know size of hash (without salt). Dim hashSizeInBits As Integer Dim hashSizeInBytes As Integer ' Make sure that hashing algorithm name is specified. If (hashAlgorithm Is Nothing) Then hashAlgorithm = "" End If ' Size of hash is based on the specified algorithm. Select hashAlgorithm.ToUpper() Case "SHA1" hashSizeInBits = 160 Case "SHA256" hashSizeInBits = 256 Case "SHA384" hashSizeInBits = 384 Case "SHA512" hashSizeInBits = 512 Case Else ' Must be MD5 hashSizeInBits = 128 End Select ' Convert size of hash from bits to bytes. hashSizeInBytes = hashSizeInBits / 8 ' Make sure that the specified hash value is long enough. If (hashWithSaltBytes.Length < hashSizeInBytes) Then VerifyHash = False End If ' Allocate array to hold original salt bytes retrieved from hash. Dim saltBytes() As Byte = New Byte(hashWithSaltBytes.Length - _ hashSizeInBytes - 1) {} ' Copy salt from the end of the hash to the new array. Dim I As Integer For I = 0 To saltBytes.Length - 1 saltBytes(I) = hashWithSaltBytes(hashSizeInBytes + I) Next I ' Compute a new hash string. Dim expectedHashString As String expectedHashString = ComputeHash(plainText, hashAlgorithm, saltBytes) ' If the computed hash matches the specified hash, ' the plain text value must be correct. VerifyHash = (hashValue = expectedHashString) End Function End Class ' <summary> ' The main entry point for the application. ' </summary> Sub Main() Dim password As String ' original password Dim wrongPassword As String ' wrong password password = "myP@5sw0rd" wrongPassword = "password" Dim passwordHashMD5 As String Dim passwordHashSha1 As String Dim passwordHashSha256 As String Dim passwordHashSha384 As String Dim passwordHashSha512 As String passwordHashMD5 = _ SimpleHash.ComputeHash(password, "MD5", Nothing) passwordHashSha1 = _ SimpleHash.ComputeHash(password, "SHA1", Nothing) passwordHashSha256 = _ SimpleHash.ComputeHash(password, "SHA256", Nothing) passwordHashSha384 = _ SimpleHash.ComputeHash(password, "SHA384", Nothing) passwordHashSha512 = _ SimpleHash.ComputeHash(password, "SHA512", Nothing) Console.WriteLine("COMPUTING HASH VALUES") Console.WriteLine("") Console.WriteLine("MD5 : {0}", passwordHashMD5) Console.WriteLine("SHA1 : {0}", passwordHashSha1) Console.WriteLine("SHA256: {0}", passwordHashSha256) Console.WriteLine("SHA384: {0}", passwordHashSha384) Console.WriteLine("SHA512: {0}", passwordHashSha512) Console.WriteLine("") Console.WriteLine("COMPARING PASSWORD HASHES") Console.WriteLine("") Console.WriteLine("MD5 (good): {0}", _ SimpleHash.VerifyHash( _ password, "MD5", _ passwordHashMD5).ToString()) Console.WriteLine("MD5 (bad) : {0}", _ SimpleHash.VerifyHash( _ wrongPassword, "MD5", _ passwordHashMD5).ToString()) Console.WriteLine("SHA1 (good): {0}", _ SimpleHash.VerifyHash( _ password, "SHA1", _ passwordHashSha1).ToString()) Console.WriteLine("SHA1 (bad) : {0}", _ SimpleHash.VerifyHash( _ wrongPassword, "SHA1", _ passwordHashSha1).ToString()) Console.WriteLine("SHA256 (good): {0}", _ SimpleHash.VerifyHash( _ password, "SHA256", _ passwordHashSha256).ToString()) Console.WriteLine("SHA256 (bad) : {0}", _ SimpleHash.VerifyHash( _ wrongPassword, "SHA256", _ passwordHashSha256).ToString()) Console.WriteLine("SHA384 (good): {0}", _ SimpleHash.VerifyHash( _ password, "SHA384", _ passwordHashSha384).ToString()) Console.WriteLine("SHA384 (bad) : {0}", _ SimpleHash.VerifyHash( _ wrongPassword, "SHA384", _ passwordHashSha384).ToString()) Console.WriteLine("SHA512 (good): {0}", _ SimpleHash.VerifyHash( _ password, "SHA512", _ passwordHashSha512).ToString()) Console.WriteLine("SHA512 (bad) : {0}", _ SimpleHash.VerifyHash( _ wrongPassword, "SHA512", _ passwordHashSha512).ToString()) End Sub End Module ' ' END OF FILE ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' Code Output COMPUTING HASH VALUES MD5 : SC4LSYSAkKILp2rPW1ZVpOP1WK7g SHA1 : E0CfoAleTy9lDL8PmqLlY76jg3k/as3G5DPe SHA256: p4OqMcDW33DzkGR7+UskcFv75yq/Jb7K49mRwRYHLdw0+HTwq3sS SHA384: Tq6F1p1Hhan+tGPLOS+T6ltPh7wvTtPqgvgd4BKCTPEGnXCOEQpcrm0IELEjnobkWKY9... SHA512: UjtzgRAx4BWpMKYb1Qnrhn3Nlj84MrKNX1zJbNW33saM9IEtRmpzn4Ny6Y5oITg3TkSZ... COMPARING PASSWORD HASHES MD5 (good): True MD5 (bad) : False SHA1 (good): True SHA1 (bad) : False SHA256 (good): True SHA256 (bad) : False SHA384 (good): True SHA384 (bad) : False SHA512 (good): True SHA512 (bad) : False |