From 9e0fbac6d3cb4e11efdb33c339ccf0adbca0bc6c Mon Sep 17 00:00:00 2001
From: ivarlovlie <git@ivarlovlie.no>
Date: Thu, 1 Apr 2021 22:36:59 +0200
Subject: Initial commit

---
 src/IOL.Helpers/PasswordHelpers.cs | 70 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 src/IOL.Helpers/PasswordHelpers.cs

(limited to 'src/IOL.Helpers/PasswordHelpers.cs')

diff --git a/src/IOL.Helpers/PasswordHelpers.cs b/src/IOL.Helpers/PasswordHelpers.cs
new file mode 100644
index 0000000..5b85219
--- /dev/null
+++ b/src/IOL.Helpers/PasswordHelpers.cs
@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using System.Security.Cryptography;
+using Microsoft.AspNetCore.Cryptography.KeyDerivation;
+
+namespace IOL.Helpers
+{
+	public static class PasswordHelper
+	{
+		private const int ITERATION_COUNT = 10000;
+		private const int SALT_SIZE = 128 / 8;
+		private const KeyDerivationPrf PRF = KeyDerivationPrf.HMACSHA256;
+
+		public static string HashPassword(string value) {
+			using var rng = RandomNumberGenerator.Create();
+			var salt = new byte[SALT_SIZE];
+			rng.GetBytes(salt);
+			var subkey = KeyDerivation.Pbkdf2(value, salt, PRF, ITERATION_COUNT, 256 / 8);
+			var outputBytes = new byte[13 + salt.Length + subkey.Length];
+			WriteNetworkByteOrder(outputBytes, 1, (uint) PRF);
+			WriteNetworkByteOrder(outputBytes, 5, (uint) ITERATION_COUNT);
+			WriteNetworkByteOrder(outputBytes, 9, (uint) SALT_SIZE);
+			Buffer.BlockCopy(salt, 0, outputBytes, 13, salt.Length);
+			Buffer.BlockCopy(subkey, 0, outputBytes, 13 + SALT_SIZE, subkey.Length);
+			return Convert.ToBase64String(outputBytes);
+		}
+
+		public static bool Verify(string password, string hashedPassword) {
+			var decodedHashedPassword = Convert.FromBase64String(hashedPassword);
+			if (decodedHashedPassword.Length == 0) return false;
+			try {
+				// Read header information
+				var networkByteOrder = (KeyDerivationPrf) ReadNetworkByteOrder(decodedHashedPassword, 1);
+				var saltLength = (int) ReadNetworkByteOrder(decodedHashedPassword, 9);
+
+				// Read the salt: must be >= 128 bits
+				if (saltLength < SALT_SIZE) 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 >= 128 bits
+				var subkeyLength = decodedHashedPassword.Length - 13 - salt.Length;
+				if (subkeyLength < SALT_SIZE) 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(password, salt, networkByteOrder, ITERATION_COUNT, subkeyLength);
+				return CryptographicOperations.FixedTimeEquals(actualSubkey, expectedSubkey);
+			} catch {
+				return false;
+			}
+		}
+
+		private static uint ReadNetworkByteOrder(IReadOnlyList<byte> buffer, int offset) {
+			return ((uint) buffer[offset + 0] << 24)
+			       | ((uint) buffer[offset + 1] << 16)
+			       | ((uint) buffer[offset + 2] << 8)
+			       | buffer[offset + 3];
+		}
+
+		private static void WriteNetworkByteOrder(IList<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);
+		}
+	}
+}
\ No newline at end of file
-- 
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