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// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Runtime.CompilerServices;
using System.Security.Cryptography;
using Microsoft.AspNetCore.Cryptography.KeyDerivation;
using Microsoft.Extensions.Identity.Core;
using Microsoft.Extensions.Options;
namespace Microsoft.AspNetCore.Identity
{
/// <summary>
/// Implements the standard Identity password hashing.
/// </summary>
/// <typeparam name="TUser">The type used to represent a user.</typeparam>
public class PasswordHasher<TUser> : IPasswordHasher<TUser> where TUser : class
{
/* =======================
* HASHED PASSWORD FORMATS
* =======================
*
* Version 2:
* PBKDF2 with HMAC-SHA1, 128-bit salt, 256-bit subkey, 1000 iterations.
* (See also: SDL crypto guidelines v5.1, Part III)
* Format: { 0x00, salt, subkey }
*
* 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.)
*/
private readonly PasswordHasherCompatibilityMode _compatibilityMode;
private readonly int _iterCount;
private readonly RandomNumberGenerator _rng;
/// <summary>
/// Creates a new instance of <see cref="PasswordHasher{TUser}"/>.
/// </summary>
/// <param name="optionsAccessor">The options for this instance.</param>
public PasswordHasher(IOptions<PasswordHasherOptions> optionsAccessor = null)
{
var options = optionsAccessor?.Value ?? new PasswordHasherOptions();
_compatibilityMode = options.CompatibilityMode;
switch (_compatibilityMode)
{
case PasswordHasherCompatibilityMode.IdentityV2:
// nothing else to do
break;
case PasswordHasherCompatibilityMode.IdentityV3:
_iterCount = options.IterationCount;
if (_iterCount < 1)
{
throw new InvalidOperationException(Resources.InvalidPasswordHasherIterationCount);
}
break;
default:
throw new InvalidOperationException(Resources.InvalidPasswordHasherCompatibilityMode);
}
_rng = options.Rng;
}
// Compares two byte arrays for equality. The method is specifically written so that the loop is not optimized.
[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]
private static bool ByteArraysEqual(byte[] a, byte[] b)
{
if (a == null && b == null)
{
return true;
}
if (a == null || b == null || a.Length != b.Length)
{
return false;
}
var areSame = true;
for (var i = 0; i < a.Length; i++)
{
areSame &= (a[i] == b[i]);
}
return areSame;
}
/// <summary>
/// Returns a hashed representation of the supplied <paramref name="password"/> for the specified <paramref name="user"/>.
/// </summary>
/// <param name="user">The user whose password is to be hashed.</param>
/// <param name="password">The password to hash.</param>
/// <returns>A hashed representation of the supplied <paramref name="password"/> for the specified <paramref name="user"/>.</returns>
public virtual string HashPassword(TUser user, string password)
{
if (password == null)
{
throw new ArgumentNullException(nameof(password));
}
if (_compatibilityMode == PasswordHasherCompatibilityMode.IdentityV2)
{
return Convert.ToBase64String(HashPasswordV2(password, _rng));
}
else
{
return Convert.ToBase64String(HashPasswordV3(password, _rng));
}
}
private static byte[] HashPasswordV2(string password, RandomNumberGenerator rng)
{
const KeyDerivationPrf Pbkdf2Prf = KeyDerivationPrf.HMACSHA1; // default for Rfc2898DeriveBytes
const int Pbkdf2IterCount = 1000; // default for Rfc2898DeriveBytes
const int Pbkdf2SubkeyLength = 256 / 8; // 256 bits
const int SaltSize = 128 / 8; // 128 bits
// Produce a version 2 (see comment above) text hash.
byte[] salt = new byte[SaltSize];
rng.GetBytes(salt);
byte[] subkey = KeyDerivation.Pbkdf2(password, salt, Pbkdf2Prf, Pbkdf2IterCount, Pbkdf2SubkeyLength);
var outputBytes = new byte[1 + SaltSize + Pbkdf2SubkeyLength];
outputBytes[0] = 0x00; // format marker
Buffer.BlockCopy(salt, 0, outputBytes, 1, SaltSize);
Buffer.BlockCopy(subkey, 0, outputBytes, 1 + SaltSize, Pbkdf2SubkeyLength);
return outputBytes;
}
private byte[] HashPasswordV3(string password, RandomNumberGenerator rng)
{
return HashPasswordV3(password, rng,
prf: KeyDerivationPrf.HMACSHA256,
iterCount: _iterCount,
saltSize: 128 / 8,
numBytesRequested: 256 / 8);
}
private static byte[] HashPasswordV3(string password, RandomNumberGenerator rng, KeyDerivationPrf prf, int iterCount, int saltSize, int numBytesRequested)
{
// Produce a version 3 (see comment above) text hash.
byte[] salt = new byte[saltSize];
rng.GetBytes(salt);
byte[] 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, (uint)iterCount);
WriteNetworkByteOrder(outputBytes, 9, (uint)saltSize);
Buffer.BlockCopy(salt, 0, outputBytes, 13, salt.Length);
Buffer.BlockCopy(subkey, 0, outputBytes, 13 + saltSize, subkey.Length);
return outputBytes;
}
private static uint ReadNetworkByteOrder(byte[] buffer, int offset)
{
return ((uint)(buffer[offset + 0]) << 24)
| ((uint)(buffer[offset + 1]) << 16)
| ((uint)(buffer[offset + 2]) << 8)
| ((uint)(buffer[offset + 3]));
}
/// <summary>
/// Returns a <see cref="PasswordVerificationResult"/> indicating the result of a password hash comparison.
/// </summary>
/// <param name="user">The user whose password should be verified.</param>
/// <param name="hashedPassword">The hash value for a user's stored password.</param>
/// <param name="providedPassword">The password supplied for comparison.</param>
/// <returns>A <see cref="PasswordVerificationResult"/> indicating the result of a password hash comparison.</returns>
/// <remarks>Implementations of this method should be time consistent.</remarks>
public virtual PasswordVerificationResult VerifyHashedPassword(TUser user, string hashedPassword, string providedPassword)
{
if (hashedPassword == null)
{
throw new ArgumentNullException(nameof(hashedPassword));
}
if (providedPassword == null)
{
throw new ArgumentNullException(nameof(providedPassword));
}
byte[] decodedHashedPassword = Convert.FromBase64String(hashedPassword);
// read the format marker from the hashed password
if (decodedHashedPassword.Length == 0)
{
return PasswordVerificationResult.Failed;
}
switch (decodedHashedPassword[0])
{
case 0x00:
if (VerifyHashedPasswordV2(decodedHashedPassword, providedPassword))
{
// This is an old password hash format - the caller needs to rehash if we're not running in an older compat mode.
return (_compatibilityMode == PasswordHasherCompatibilityMode.IdentityV3)
? PasswordVerificationResult.SuccessRehashNeeded
: PasswordVerificationResult.Success;
}
else
{
return PasswordVerificationResult.Failed;
}
case 0x01:
int embeddedIterCount;
if (VerifyHashedPasswordV3(decodedHashedPassword, providedPassword, out embeddedIterCount))
{
// If this hasher was configured with a higher iteration count, change the entry now.
return (embeddedIterCount < _iterCount)
? PasswordVerificationResult.SuccessRehashNeeded
: PasswordVerificationResult.Success;
}
else
{
return PasswordVerificationResult.Failed;
}
default:
return PasswordVerificationResult.Failed; // unknown format marker
}
}
private static bool VerifyHashedPasswordV2(byte[] hashedPassword, string password)
{
const KeyDerivationPrf Pbkdf2Prf = KeyDerivationPrf.HMACSHA1; // default for Rfc2898DeriveBytes
const int Pbkdf2IterCount = 1000; // default for Rfc2898DeriveBytes
const int Pbkdf2SubkeyLength = 256 / 8; // 256 bits
const int SaltSize = 128 / 8; // 128 bits
// We know ahead of time the exact length of a valid hashed password payload.
if (hashedPassword.Length != 1 + SaltSize + Pbkdf2SubkeyLength)
{
return false; // bad size
}
byte[] salt = new byte[SaltSize];
Buffer.BlockCopy(hashedPassword, 1, salt, 0, salt.Length);
byte[] expectedSubkey = new byte[Pbkdf2SubkeyLength];
Buffer.BlockCopy(hashedPassword, 1 + salt.Length, expectedSubkey, 0, expectedSubkey.Length);
// Hash the incoming password and verify it
byte[] actualSubkey = KeyDerivation.Pbkdf2(password, salt, Pbkdf2Prf, Pbkdf2IterCount, Pbkdf2SubkeyLength);
return ByteArraysEqual(actualSubkey, expectedSubkey);
}
private static bool VerifyHashedPasswordV3(byte[] hashedPassword, string password, out int iterCount)
{
iterCount = default(int);
try
{
// Read header information
KeyDerivationPrf prf = (KeyDerivationPrf)ReadNetworkByteOrder(hashedPassword, 1);
iterCount = (int)ReadNetworkByteOrder(hashedPassword, 5);
int saltLength = (int)ReadNetworkByteOrder(hashedPassword, 9);
// Read the salt: must be >= 128 bits
if (saltLength < 128 / 8)
{
return false;
}
byte[] salt = new byte[saltLength];
Buffer.BlockCopy(hashedPassword, 13, salt, 0, salt.Length);
// Read the subkey (the rest of the payload): must be >= 128 bits
int subkeyLength = hashedPassword.Length - 13 - salt.Length;
if (subkeyLength < 128 / 8)
{
return false;
}
byte[] expectedSubkey = new byte[subkeyLength];
Buffer.BlockCopy(hashedPassword, 13 + salt.Length, expectedSubkey, 0, expectedSubkey.Length);
// Hash the incoming password and verify it
byte[] actualSubkey = KeyDerivation.Pbkdf2(password, salt, prf, iterCount, subkeyLength);
return ByteArraysEqual(actualSubkey, expectedSubkey);
}
catch
{
// This should never occur except in the case of a malformed payload, where
// we might go off the end of the array. Regardless, a malformed payload
// implies verification failed.
return false;
}
}
private static void WriteNetworkByteOrder(byte[] buffer, int offset, uint value)
{
buffer[offset + 0] = (byte)(value >> 24);
buffer[offset + 1] = (byte)(value >> 16);
buffer[offset + 2] = (byte)(value >> 8);
buffer[offset + 3] = (byte)(value >> 0);
}
}
}
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