Rfc2898 / PBKDF2 with SHA256 as digest in c#
.NET Core has a new implementation of Rfc2898DeriveBytes
.
The CoreFX version no longer has the the hashing algorithm hard-coded
The code is available on Github. It was merged to master on March 2017 and has been shipped with .NET Core 2.0.
See Bruno Garcia's answer.
Carsten: Please accept that answer rather than this one.
At the time I started this answer, Rfc2898DeriveBytes was not configurable to use a different hash function. In the meantime, though, it has been improved; see Bruno Garcia's answer. The following function can be used to generate a hashed version of a user-provided password to store in a database for authentication purposes.
For users of older .NET frameworks, this is still useful:
// NOTE: The iteration count should
// be as high as possible without causing
// unreasonable delay. Note also that the password
// and salt are byte arrays, not strings. After use,
// the password and salt should be cleared (with Array.Clear)
public static byte[] PBKDF2Sha256GetBytes(int dklen, byte[] password, byte[] salt, int iterationCount){
using(var hmac=new System.Security.Cryptography.HMACSHA256(password)){
int hashLength=hmac.HashSize/8;
if((hmac.HashSize&7)!=0)
hashLength++;
int keyLength=dklen/hashLength;
if((long)dklen>(0xFFFFFFFFL*hashLength) || dklen<0)
throw new ArgumentOutOfRangeException("dklen");
if(dklen%hashLength!=0)
keyLength++;
byte[] extendedkey=new byte[salt.Length+4];
Buffer.BlockCopy(salt,0,extendedkey,0,salt.Length);
using(var ms=new System.IO.MemoryStream()){
for(int i=0;i<keyLength;i++){
extendedkey[salt.Length]=(byte)(((i+1)>>24)&0xFF);
extendedkey[salt.Length+1]=(byte)(((i+1)>>16)&0xFF);
extendedkey[salt.Length+2]=(byte)(((i+1)>>8)&0xFF);
extendedkey[salt.Length+3]=(byte)(((i+1))&0xFF);
byte[] u=hmac.ComputeHash(extendedkey);
Array.Clear(extendedkey,salt.Length,4);
byte[] f=u;
for(int j=1;j<iterationCount;j++){
u=hmac.ComputeHash(u);
for(int k=0;k<f.Length;k++){
f[k]^=u[k];
}
}
ms.Write(f,0,f.Length);
Array.Clear(u,0,u.Length);
Array.Clear(f,0,f.Length);
}
byte[] dk=new byte[dklen];
ms.Position=0;
ms.Read(dk,0,dklen);
ms.Position=0;
for(long i=0;i<ms.Length;i++){
ms.WriteByte(0);
}
Array.Clear(extendedkey,0,extendedkey.Length);
return dk;
}
}
For those who need it, .NET Framework 4.7.2 includes an overload of Rfc2898DeriveBytes that allows the hashing algorithm to be specified:
byte[] bytes;
using (var deriveBytes = new Rfc2898DeriveBytes(password, salt, iterations, HashAlgorithmName.SHA256))
{
bytes = deriveBytes.GetBytes(PBKDF2SubkeyLength);
}
The HashAlgorithmName options at the moment are:
- MD5
- SHA1
- SHA256
- SHA384
- SHA512