Hash and salt passwords in C

Question

I was just going through one of DavidHayden s articles on Hashing User Passwords   Really I can t get what he is trying to achieve   Here is his code   private static string CreateSalt int size          Generate a cryptographic random number      RNGCryptoServiceProvider rng   new RNGCryptoServiceProvider        byte   buff   new byte size       rng GetBytes buff           Return a Base64 string representation of the random number      return Convert ToBase64String buff      private static string CreatePasswordHash string pwd  string salt        string saltAndPwd   String Concat pwd  salt       string hashedPwd           FormsAuthentication HashPasswordForStoringInConfigFile          saltAndPwd   sha1        return hashedPwd      Is there any other C  method for hashing passwords and adding salt to it

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In answer to this part of the original question  Is there any other C  method for hashing passwords  You can achieve this using ASP NET Identity v3 0 https   www nuget org packages Microsoft AspNet Identity EntityFramework 3 0 0-rc1-final  using System  using System Collections Generic  using System Linq  using System Text  using System Threading Tasks  using Microsoft AspNet Identity  using System Security Principal   namespace HashTest        class Program               static void Main string   args                         WindowsIdentity wi   WindowsIdentity GetCurrent                 var ph   new PasswordHasher lt WindowsIdentity gt                  Console WriteLine ph HashPassword wi  test                  Console WriteLine ph VerifyHashedPassword wi  AQAAAAEAACcQAAAAEA5S5X7dmbx NzTk6ixCX bi8zbKqBUjBhID3Dg1teh TRZMkAy3CZC5yIfbLqwk2A     test

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Use the System Web Helpers Crypto NuGet package from Microsoft  It automatically adds salt to the hash   You hash a password like this  var hash   Crypto HashPassword  foo     You verify a password like this  var verified   Crypto VerifyHashedPassword hash   foo

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Salt is used to add an extra level of complexity to the hash  to make it harder to brute-force crack   From an article on Sitepoint      A hacker can still perform   what s called a dictionary attack    Malicious parties may make a   dictionary attack by taking  for   instance  100 000 passwords that they   know people use frequently  e g  city   names  sports teams  etc    hash them    and then compare each entry in the   dictionary against each row in the   database table  If the hackers find a   match  bingo  They have your password    To solve this problem  however  we   need only salt the hash       To salt a hash  we simply come up with   a random-looking string of text    concatenate it with the password   supplied by the user  then hash both   the randomly generated string and   password together as one value  We   then save both the hash and the salt   as separate fields within the Users   table       In this scenario  not only would a   hacker need to guess the password    they d have to guess the salt as well    Adding salt to the clear text improves   security  now  if a hacker tries a   dictionary attack  he must hash his   100 000 entries with the salt of every   user row  Although it s still   possible  the chances of hacking   success diminish radically    There is no method automatically doing this in  NET  so you ll have go with the solution above

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I ve been reading that hashing functions like SHA256 weren t really intended for use with storing passwords  https   patrickmn com security storing-passwords-securely  notpasswordhashes  Instead adaptive key derivation functions like PBKDF2  bcrypt or scrypt were  Here is a PBKDF2 based one that Microsoft wrote for PasswordHasher in their Microsoft AspNet Identity library                                 HASHED PASSWORD FORMATS                                   Version 3     PBKDF2 with HMAC-SHA256  128-bit salt  256-bit subkey  10000 iterations     Format    0x01  prf  UInt32   iter count  UInt32   salt length  UInt32   salt  subkey       All UInt32s are stored big-endian        public string HashPassword string password        var prf   KeyDerivationPrf HMACSHA256      var rng   RandomNumberGenerator Create        const int iterCount   10000      const int saltSize   128   8      const int numBytesRequested   256   8          Produce a version 3  see comment above  text hash      var salt   new byte saltSize       rng GetBytes salt       var subkey   KeyDerivation Pbkdf2 password  salt  prf  iterCount  numBytesRequested        var outputBytes   new byte 13   salt Length   subkey Length       outputBytes 0    0x01     format marker     WriteNetworkByteOrder outputBytes  1   uint prf       WriteNetworkByteOrder outputBytes  5  iterCount       WriteNetworkByteOrder outputBytes  9  saltSize       Buffer BlockCopy salt  0  outputBytes  13  salt Length       Buffer BlockCopy subkey  0  outputBytes  13   saltSize  subkey Length       return Convert ToBase64String outputBytes      public bool VerifyHashedPassword string hashedPassword  string providedPassword        var decodedHashedPassword   Convert FromBase64String hashedPassword           Wrong version     if  decodedHashedPassword 0     0x01          return false          Read header information     var prf    KeyDerivationPrf ReadNetworkByteOrder decodedHashedPassword  1       var iterCount    int ReadNetworkByteOrder decodedHashedPassword  5       var saltLength    int ReadNetworkByteOrder decodedHashedPassword  9           Read the salt  must be  gt   128 bits     if  saltLength  lt  128   8                return false            var salt   new byte saltLength       Buffer BlockCopy decodedHashedPassword  13  salt  0  salt Length           Read the subkey  the rest of the payload   must be  gt   128 bits     var subkeyLength   decodedHashedPassword Length - 13 - salt Length      if  subkeyLength  lt  128   8                return false            var expectedSubkey   new byte subkeyLength       Buffer BlockCopy decodedHashedPassword  13   salt Length  expectedSubkey  0  expectedSubkey Length           Hash the incoming password and verify it     var actualSubkey   KeyDerivation Pbkdf2 providedPassword  salt  prf  iterCount  subkeyLength       return actualSubkey SequenceEqual expectedSubkey      private static void WriteNetworkByteOrder byte   buffer  int offset  uint value        buffer offset   0     byte  value  gt  gt  24       buffer offset   1     byte  value  gt  gt  16       buffer offset   2     byte  value  gt  gt  8       buffer offset   3     byte  value  gt  gt  0      private static uint ReadNetworkByteOrder byte   buffer  int offset        return   uint  buffer offset   0    lt  lt  24              uint  buffer offset   1    lt  lt  16              uint  buffer offset   2    lt  lt  8              uint  buffer offset   3         Note this requires Microsoft AspNetCore Cryptography KeyDerivation nuget package installed which requires  NET Standard 2 0   NET 4 6 1 or higher   For earlier versions of  NET see the Crypto class from Microsoft s System Web Helpers library   Update Nov 2015 Updated answer to use an implementation from a different Microsoft library which uses PBKDF2-HMAC-SHA256 hashing instead of PBKDF2-HMAC-SHA1  note PBKDF2-HMAC-SHA1 is still secure if iterCount is high enough   You can check out the source the simplified code was copied from as it actually handles validating and upgrading hashes implemented from previous answer  useful if you need to increase iterCount in the future

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I read all answers and I think those enough  specially  Michael articles with slow hashing and  CodesInChaos good comments  but I decided to share my code snippet for hashing validating that may be useful and it does not require  Microsoft AspNet Cryptography KeyDerivation        private static bool SlowEquals byte   a  byte   b                                uint diff    uint a Length    uint b Length                  for  int i   0  i  lt  a Length  amp  amp  i  lt  b Length  i                        diff     uint  a i    b i                    return diff    0                     private static byte   PBKDF2 string password  byte   salt  int iterations  int outputBytes                                Rfc2898DeriveBytes pbkdf2   new Rfc2898DeriveBytes password  salt                   pbkdf2 IterationCount   iterations                  return pbkdf2 GetBytes outputBytes                      private static string CreateHash string value  int salt bytes  int hash bytes  int pbkdf2 iterations                                   Generate a random salt                 RNGCryptoServiceProvider csprng   new RNGCryptoServiceProvider                    byte   salt   new byte salt bytes                   csprng GetBytes salt                       Hash the value and encode the parameters                 byte   hash   PBKDF2 value  salt  pbkdf2 iterations  hash bytes                      You need to return the salt value too for the validation process                 return Convert ToBase64String hash                                  Convert ToBase64String hash                      private static bool ValidateHash string pureVal  string saltVal  string hashVal  int pbkdf2 iterations                                try                                       byte   salt   Convert FromBase64String saltVal                       byte   hash   Convert FromBase64String hashVal                        byte   testHash   PBKDF2 pureVal  salt  pbkdf2 iterations  hash Length                       return SlowEquals hash  testHash                                     catch  Exception ex                                        return false                                    Please pay attention SlowEquals function that is so important  Finally  I hope this help and Please don t hesitate to advise me about better approaches

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protected void m GenerateSHA256 Button1 Click objectSender  EventArgs e    string salt  createSalt 10   string hashedPassword GenerateSHA256Hash m UserInput TextBox Text Salt   m SaltHash TextBox Text Salt   m SaltSHA256Hash TextBox Text hashedPassword      public string createSalt int size     var rng  new System Security Cyptography RNGCyptoServiceProvider     var buff  new byte size   rng GetBytes buff    return Convert ToBase64String buff        public string GenerateSHA256Hash string input string salt     byte  bytes System Text Encoding UTF8 GetBytes input salt    new System Security Cyptography SHA256Managed     byte  hash sha256hashString ComputedHash bytes    return bytesArrayToHexString hash

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This is how I do it   I create the hash and store it using the ProtectedData api       public static string GenerateKeyHash string Password                if  string IsNullOrEmpty Password   return null          if  Password Length  lt  1  return null           byte   salt   new byte 20           byte   key   new byte 20           byte   ret   new byte 40            try                       using  RNGCryptoServiceProvider randomBytes   new RNGCryptoServiceProvider                                  randomBytes GetBytes salt                    using  var hashBytes   new Rfc2898DeriveBytes Password  salt  10000                                         key   hashBytes GetBytes 20                       Buffer BlockCopy salt  0  ret  0  20                       Buffer BlockCopy key  0  ret  20  20                                                  returns salt key pair             return Convert ToBase64String ret                     finally                       if  salt    null                  Array Clear salt  0  salt Length               if  key    null                  Array Clear key  0  key Length               if  ret    null                  Array Clear ret  0  ret Length                         public static bool ComparePasswords string PasswordHash  string Password                if  string IsNullOrEmpty PasswordHash     string IsNullOrEmpty Password   return false          if  PasswordHash Length  lt  40    Password Length  lt  1  return false           byte   salt   new byte 20           byte   key   new byte 20           byte   hash   Convert FromBase64String PasswordHash            try                       Buffer BlockCopy hash  0  salt  0  20               Buffer BlockCopy hash  20  key  0  20                using  var hashBytes   new Rfc2898DeriveBytes Password  salt  10000                                 byte   newKey   hashBytes GetBytes 20                    if  newKey    null                      if  newKey SequenceEqual key                           return true                            return false                    finally                       if  salt    null                  Array Clear salt  0  salt Length               if  key    null                  Array Clear key  0  key Length               if  hash    null                  Array Clear hash  0  hash Length                        public static byte   DecryptData string Data  byte   Salt                if  string IsNullOrEmpty Data   return null           byte   btData   Convert FromBase64String Data            try                       return ProtectedData Unprotect btData  Salt  DataProtectionScope CurrentUser                     finally                       if  btData    null                  Array Clear btData  0  btData Length                        public static string EncryptData byte   Data  byte   Salt                if  Data    null  return null          if  Data Length  lt  1  return null           byte   buffer   new byte Data Length            try                       Buffer BlockCopy Data  0  buffer  0  Data Length               return System Convert ToBase64String ProtectedData Protect buffer  Salt  DataProtectionScope CurrentUser                      finally                       if  buffer    null                  Array Clear buffer  0  buffer Length

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I created a class that  has the following method   Create Salt  Hash Input  Validate input public class CryptographyProcessor       public string CreateSalt int size                  Generate a cryptographic random number          RNGCryptoServiceProvider rng   new RNGCryptoServiceProvider            byte   buff   new byte size           rng GetBytes buff           return Convert ToBase64String buff              public string GenerateHash string input  string salt                 byte   bytes   Encoding UTF8 GetBytes input   salt           SHA256Managed sHA256ManagedString   new SHA256Managed            byte   hash   sHA256ManagedString ComputeHash bytes           return Convert ToBase64String hash              public bool AreEqual string plainTextInput  string hashedInput  string salt                string newHashedPin   GenerateHash plainTextInput  salt           return newHashedPin Equals hashedInput

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Bah  this is better  http   sourceforge net projects pwdtknet  and it is better because       it performs Key Stretching AND uses HMACSHA512

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If you dont use asp net or  net core there is also an easy way in     Net Standard 2 0 projects   First you can set the desired size of the hash  salt and iteration number which is related to the duration of the hash generation   private const int SaltSize   32  private const int HashSize   32  private const int IterationCount   10000    To generare the password hash and salt you can use something like this   public static string GeneratePasswordHash string password  out string salt        using  Rfc2898DeriveBytes rfc2898DeriveBytes   new Rfc2898DeriveBytes password  SaltSize                 rfc2898DeriveBytes IterationCount   IterationCount          byte   hashData   rfc2898DeriveBytes GetBytes HashSize           byte   saltData   rfc2898DeriveBytes Salt          salt   Convert ToBase64String saltData           return Convert ToBase64String hashData             To verify if the password which the user entered is valid you can check with the values in your database   public static bool VerifyPassword string password  string passwordHash  string salt        using  Rfc2898DeriveBytes rfc2898DeriveBytes   new Rfc2898DeriveBytes password  SaltSize                 rfc2898DeriveBytes IterationCount   IterationCount          rfc2898DeriveBytes Salt   Convert FromBase64String salt           byte   hashData   rfc2898DeriveBytes GetBytes HashSize           return Convert ToBase64String hashData     passwordHash            The following unit test shows the usage   string password    MySecret    string passwordHash   PasswordHasher GeneratePasswordHash password  out string salt    Assert True PasswordHasher VerifyPassword password  passwordHash  salt    Assert False PasswordHasher VerifyPassword password ToUpper    passwordHash  salt      Microsoft Rfc2898DeriveBytes Source

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Actually this is kind of strange  with the string conversions - which the membership provider does to put them into config files  Hashes and salts are binary blobs  you don t need to convert them to strings unless you want to put them into text files    In my book  Beginning ASP NET Security   oh finally  an excuse to pimp the book  I do the following  static byte   GenerateSaltedHash byte   plainText  byte   salt      HashAlgorithm algorithm   new SHA256Managed       byte   plainTextWithSaltBytes        new byte plainText Length   salt Length      for  int i   0  i  lt  plainText Length  i            plainTextWithSaltBytes i    plainText i         for  int i   0  i  lt  salt Length  i            plainTextWithSaltBytes plainText Length   i    salt i          return algorithm ComputeHash plainTextWithSaltBytes                   The salt generation is as the example in the question  You can convert text to byte arrays using Encoding UTF8 GetBytes string   If you must convert a hash to its string representation you can use Convert ToBase64String and Convert FromBase64String to convert it back   You should note that you cannot use the equality operator on byte arrays  it checks references and so you should simply loop through both arrays checking each byte thus  public static bool CompareByteArrays byte   array1  byte   array2      if  array1 Length    array2 Length          return false         for  int i   0  i  lt  array1 Length  i            if  array1 i     array2 i               return false               return true      Always use a new salt per password  Salts do not have to be kept secret and can be stored alongside the hash itself

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What blowdart said  but with a little less code  Use Linq or CopyTo to concatenate arrays  public static byte   Hash string value  byte   salt        return Hash Encoding UTF8 GetBytes value   salt      public static byte   Hash byte   value  byte   salt        byte   saltedValue   value Concat salt  ToArray           Alternatively use CopyTo        var saltedValue   new byte value Length   salt Length         value CopyTo saltedValue  0         salt CopyTo saltedValue  value Length        return new SHA256Managed   ComputeHash saltedValue      Linq has an easy way to compare your byte arrays too  public bool ConfirmPassword string password        byte   passwordHash   Hash password   passwordSalt        return  passwordHash SequenceEqual passwordHash      Before implementing any of this however  check out this post  For password hashing you may want a slow hash algorithm  not a fast one  To that end there is the Rfc2898DeriveBytes class which is slow  and can be made slower   and may answer the second part of the original question in that it can take a password and salt and return a hash  See this question for more information  Note  Stack Exchange is using Rfc2898DeriveBytes for password hashing  source code here

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I have made a library SimpleHashing Net to make the process of hashing easy with basic classes provided by Microsoft  Ordinary SHA is not really enough to have passwords stored securely anymore   The library use the idea of hash format from Bcrypt  but since there is no official MS implementation I prefer to use what s available in the framework  i e  PBKDF2   but it s a bit too hard out of the box   This is a quick example how to use the library   ISimpleHash simpleHash   new SimpleHash        Creating a user hash  hashedPassword can be stored in a database    hashedPassword contains the number of iterations and salt inside it similar to bcrypt format string hashedPassword   simpleHash Compute  Password123        Validating user s password by first loading it from database by username string storedHash    repository GetUserPasswordHash username   isPasswordValid   simpleHash Verify  Password123   storedHash

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create proc  dbo   hash pass   family nvarchar 50    username nvarchar 50    pass nvarchar Max       semat nvarchar 50    tell nvarchar 50   as insert into tbl karbar values   family  username  select HASHBYTES  SHA1    pass    semat  tell

[c#] Hash and salt passwords in C#

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