How to read Brave Browser cookie database encrypted values in C# (.NET Core)?

Question

I am attempting to read the encrypted values of cookies using a C# console app.

My cookie reader class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;
using Microsoft.EntityFrameworkCore;

namespace ConsoleApp1.Models
{
    public class ChromeCookieReader
    {
        public IEnumerable<Tuple<string, string>> ReadCookies(string hostName)
        {
            if (hostName == null) throw new ArgumentNullException("hostName");

            using var context = new ChromeCookieDbContext();

            var cookies = context
                .Cookies
                .Where(c => c.HostKey.Equals("localhost"))
                .AsNoTracking();

            foreach (var cookie in cookies)
            {
                var decodedData = ProtectedData
                    .Unprotect(cookie.EncryptedValue,
                        null, 
                        DataProtectionScope.CurrentUser);

                var decodedValue = Encoding.UTF8.GetString(decodedData);

                yield return Tuple.Create(cookie.Name, decodedValue);
            }
        }
    }
}

My EF DbContext

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
using System.Text;
using Microsoft.EntityFrameworkCore;

namespace ConsoleApp1.Models
{
    public class Cookie
    {
        [Column("host_key")]
        public string HostKey { get; set; }

        [Column("name")] 
        public string Name { get; set; }

        [Column("encrypted_value")]
        public byte[] EncryptedValue { get; set; }
    }

    public class ChromeCookieDbContext : DbContext
    {
        public DbSet<Cookie> Cookies { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            // var dbPath = Environment.GetFolderPath(
            //    Environment.SpecialFolder.LocalApplicationData) 
            //             + @"\Google\Chrome\User Data\Default\Cookies";

            var dbPath = Environment.GetFolderPath(
                             Environment.SpecialFolder.LocalApplicationData)
                         + @"\BraveSoftware\Brave-Browser\User Data\Default\Cookies";

            if (!System.IO.File.Exists(dbPath)) throw new System.IO.FileNotFoundException("Cant find cookie store", dbPath); // race condition, but i'll risk it

            var connectionString = "Data Source=" + dbPath + ";Mode=ReadOnly;";

            optionsBuilder
                .UseSqlite(connectionString);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Cookie>().ToTable("cookies").HasNoKey();
        }
    }
}

My attempted solution was inspired by Encrypted cookies in Chrome however it doesn't look like it'll work the same despite Brave Browser being based on Chromium. Instead the Windows Data Protection API throws an exception.

Internal.Cryptography.CryptoThrowHelper.WindowsCryptographicException
  HResult=0x0000000D
  Message=The data is invalid.
  Source=System.Security.Cryptography.ProtectedData
  StackTrace:
   at System.Security.Cryptography.ProtectedData.ProtectOrUnprotect(Byte[] inputData, Byte[] optionalEntropy, DataProtectionScope scope, Boolean protect)
   at System.Security.Cryptography.ProtectedData.Unprotect(Byte[] encryptedData, Byte[] optionalEntropy, DataProtectionScope scope)
   at ConsoleApp1.Models.ChromeCookieReader.<ReadCookies>d__0.MoveNext()

Other known issues: If Brave is open EF Core "freaks out" that the SQLite database is locked and won't read anything.

Thermoelectrometer

Answer 1

In Chromium version 80 and up, Google modified the way that cookies are encrypted to provide additional security to users. You cannot pass cookies to the Windows DPAPI directly for decryption anymore. Rather Chrome's Local State stores an encryption key that is decrypted with the Windows DPAI, you have to use that key to decrypt the cookies. I am giving credit where it's due as I did not find this out on my own and used information from the answer at https://mcmap.net/q/57478/-dpapi-fails-with-cryptographicexception-when-trying-to-decrypt-chrome-cookies to fix my issue.

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using System.Security.Cryptography;
using Newtonsoft.Json.Linq;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Parameters;

namespace BraveBrowserCookieReaderDemo
{
    public class BraveCookieReader
    {
        public IEnumerable<Tuple<string, string>> ReadCookies(string hostName)
        {
            if (hostName == null) throw new ArgumentNullException("hostName");

            using var context = new BraveCookieDbContext();

            var cookies = context
                .Cookies
                .Where(c => c.HostKey.Equals(hostName))
                .AsNoTracking();

            // Big thanks to https://mcmap.net/q/57478/-dpapi-fails-with-cryptographicexception-when-trying-to-decrypt-chrome-cookies for answering how Chrome 80 and up changed the way cookies are encrypted.

            string encKey = File.ReadAllText(System.Environment.GetEnvironmentVariable("LOCALAPPDATA") + @"\BraveSoftware\Brave-Browser\User Data\Local State");
            encKey = JObject.Parse(encKey)["os_crypt"]["encrypted_key"].ToString();
            var decodedKey = System.Security.Cryptography.ProtectedData.Unprotect(Convert.FromBase64String(encKey).Skip(5).ToArray(), null, System.Security.Cryptography.DataProtectionScope.LocalMachine);

            foreach (var cookie in cookies)
            {

                var data = cookie.EncryptedValue;

                var decodedValue = _decryptWithKey(data, decodedKey, 3);


                yield return Tuple.Create(cookie.Name, decodedValue);
            }
        }


        private string _decryptWithKey(byte[] message, byte[] key, int nonSecretPayloadLength)
        {
            const int KEY_BIT_SIZE = 256;
            const int MAC_BIT_SIZE = 128;
            const int NONCE_BIT_SIZE = 96;

            if (key == null || key.Length != KEY_BIT_SIZE / 8)
                throw new ArgumentException(String.Format("Key needs to be {0} bit!", KEY_BIT_SIZE), "key");
            if (message == null || message.Length == 0)
                throw new ArgumentException("Message required!", "message");

            using (var cipherStream = new MemoryStream(message))
            using (var cipherReader = new BinaryReader(cipherStream))
            {
                var nonSecretPayload = cipherReader.ReadBytes(nonSecretPayloadLength);
                var nonce = cipherReader.ReadBytes(NONCE_BIT_SIZE / 8);
                var cipher = new GcmBlockCipher(new AesEngine());
                var parameters = new AeadParameters(new KeyParameter(key), MAC_BIT_SIZE, nonce);
                cipher.Init(false, parameters);
                var cipherText = cipherReader.ReadBytes(message.Length);
                var plainText = new byte[cipher.GetOutputSize(cipherText.Length)];
                try
                {
                    var len = cipher.ProcessBytes(cipherText, 0, cipherText.Length, plainText, 0);
                    cipher.DoFinal(plainText, len);
                }
                catch (InvalidCipherTextException)
                {
                    return null;
                }
                return Encoding.Default.GetString(plainText);
            }
        }
    }
}

Thermoelectrometer