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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Diagnostics;
using System.Text;
using Microsoft.AspNetCore.Cryptography.Cng;
using Microsoft.AspNetCore.Cryptography.SafeHandles;
namespace Microsoft.AspNetCore.Cryptography.KeyDerivation.PBKDF2;
/// <summary>
/// A PBKDF2 provider which utilizes the Win7 API BCryptDeriveKeyPBKDF2.
/// </summary>
internal sealed unsafe class Win7Pbkdf2Provider : IPbkdf2Provider
{
public byte[] DeriveKey(string password, byte[] salt, KeyDerivationPrf prf, int iterationCount, int numBytesRequested)
{
Debug.Assert(password != null);
Debug.Assert(salt != null);
Debug.Assert(iterationCount > 0);
Debug.Assert(numBytesRequested > 0);
byte dummy; // CLR doesn't like pinning zero-length buffers, so this provides a valid memory address when working with zero-length buffers
// Don't dispose of this algorithm instance; it is cached and reused!
var algHandle = PrfToCachedCngAlgorithmInstance(prf);
// Convert password string to bytes.
// Allocate on the stack whenever we can to save allocations.
int cbPasswordBuffer = Encoding.UTF8.GetMaxByteCount(password.Length);
fixed (byte* pbHeapAllocatedPasswordBuffer = (cbPasswordBuffer > Constants.MAX_STACKALLOC_BYTES) ? new byte[cbPasswordBuffer] : null)
{
byte* pbPasswordBuffer = pbHeapAllocatedPasswordBuffer;
if (pbPasswordBuffer == null)
{
if (cbPasswordBuffer == 0)
{
pbPasswordBuffer = &dummy;
}
else
{
byte* pbStackAllocPasswordBuffer = stackalloc byte[cbPasswordBuffer]; // will be released when the frame unwinds
pbPasswordBuffer = pbStackAllocPasswordBuffer;
}
}
try
{
int cbPasswordBufferUsed; // we're not filling the entire buffer, just a partial buffer
fixed (char* pszPassword = password)
{
cbPasswordBufferUsed = Encoding.UTF8.GetBytes(pszPassword, password.Length, pbPasswordBuffer, cbPasswordBuffer);
}
fixed (byte* pbHeapAllocatedSalt = salt)
{
byte* pbSalt = (pbHeapAllocatedSalt != null) ? pbHeapAllocatedSalt : &dummy;
byte[] retVal = new byte[numBytesRequested];
fixed (byte* pbRetVal = retVal)
{
int ntstatus = UnsafeNativeMethods.BCryptDeriveKeyPBKDF2(
hPrf: algHandle,
pbPassword: pbPasswordBuffer,
cbPassword: (uint)cbPasswordBufferUsed,
pbSalt: pbSalt,
cbSalt: (uint)salt.Length,
cIterations: (ulong)iterationCount,
pbDerivedKey: pbRetVal,
cbDerivedKey: (uint)retVal.Length,
dwFlags: 0);
UnsafeNativeMethods.ThrowExceptionForBCryptStatus(ntstatus);
}
return retVal;
}
}
finally
{
UnsafeBufferUtil.SecureZeroMemory(pbPasswordBuffer, cbPasswordBuffer);
}
}
}
private static BCryptAlgorithmHandle PrfToCachedCngAlgorithmInstance(KeyDerivationPrf prf)
{
switch (prf)
{
case KeyDerivationPrf.HMACSHA1:
return CachedAlgorithmHandles.HMAC_SHA1;
case KeyDerivationPrf.HMACSHA256:
return CachedAlgorithmHandles.HMAC_SHA256;
case KeyDerivationPrf.HMACSHA512:
return CachedAlgorithmHandles.HMAC_SHA512;
default:
throw CryptoUtil.Fail("Unrecognized PRF.");
}
}
}
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