Restore SEBPatch
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SafeExamBrowser.Configuration/Cryptography/PasswordEncryption.cs
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223
SafeExamBrowser.Configuration/Cryptography/PasswordEncryption.cs
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/*
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* Copyright (c) 2024 ETH Zürich, IT Services
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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using System.IO;
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using System.Linq;
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using System.Security.Cryptography;
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using SafeExamBrowser.Configuration.Contracts;
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using SafeExamBrowser.Configuration.Contracts.Cryptography;
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using SafeExamBrowser.Logging.Contracts;
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namespace SafeExamBrowser.Configuration.Cryptography
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{
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public class PasswordEncryption : IPasswordEncryption
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{
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private const int BLOCK_SIZE = 16;
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private const int HEADER_SIZE = 2;
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private const int ITERATIONS = 10000;
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private const int KEY_SIZE = 32;
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private const int OPTIONS = 0x1;
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private const int SALT_SIZE = 8;
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private const int VERSION = 0x2;
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private ILogger logger;
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public PasswordEncryption(ILogger logger)
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{
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this.logger = logger;
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}
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public LoadStatus Decrypt(Stream data, string password, out Stream decrypted)
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{
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decrypted = default(Stream);
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if (password == null)
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{
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return LoadStatus.PasswordNeeded;
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}
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var (version, options) = ParseHeader(data);
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var (authenticationKey, encryptionKey) = GenerateKeysForDecryption(data, password);
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var (originalHmac, computedHmac) = GenerateHmacForDecryption(authenticationKey, data);
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if (!computedHmac.SequenceEqual(originalHmac))
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{
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return FailForInvalidHmac();
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}
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decrypted = Decrypt(data, encryptionKey, originalHmac.Length);
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return LoadStatus.Success;
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}
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public SaveStatus Encrypt(Stream data, string password, out Stream encrypted)
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{
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var (authKey, authSalt, encrKey, encrSalt) = GenerateKeysForEncryption(password);
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encrypted = Encrypt(data, encrKey, out var initVector);
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encrypted = WriteEncryptionParameters(authKey, authSalt, encrSalt, initVector, encrypted);
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return SaveStatus.Success;
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}
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private (int version, int options) ParseHeader(Stream data)
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{
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data.Seek(0, SeekOrigin.Begin);
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logger.Debug("Parsing encryption header...");
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var version = data.ReadByte();
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var options = data.ReadByte();
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if (version != VERSION || options != OPTIONS)
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{
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logger.Debug($"Unknown encryption header! Expected: [{VERSION},{OPTIONS},...] - Actual: [{version},{options},...]");
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}
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return (version, options);
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}
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private (byte[] authenticationKey, byte[] encryptionKey) GenerateKeysForDecryption(Stream data, string password)
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{
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var authenticationSalt = new byte[SALT_SIZE];
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var encryptionSalt = new byte[SALT_SIZE];
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logger.Debug("Generating keys for authentication and decryption...");
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data.Seek(HEADER_SIZE, SeekOrigin.Begin);
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data.Read(encryptionSalt, 0, SALT_SIZE);
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data.Read(authenticationSalt, 0, SALT_SIZE);
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using (var authenticationGenerator = new Rfc2898DeriveBytes(password, authenticationSalt, ITERATIONS))
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using (var encryptionGenerator = new Rfc2898DeriveBytes(password, encryptionSalt, ITERATIONS))
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{
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var authenticationKey = authenticationGenerator.GetBytes(KEY_SIZE);
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var encryptionKey = encryptionGenerator.GetBytes(KEY_SIZE);
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return (authenticationKey, encryptionKey);
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}
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}
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private (byte[] authKey, byte[] authSalt, byte[] encrKey, byte[] encrSalt) GenerateKeysForEncryption(string password)
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{
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logger.Debug("Generating keys for authentication and encryption...");
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using (var authenticationGenerator = new Rfc2898DeriveBytes(password, SALT_SIZE, ITERATIONS))
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using (var encryptionGenerator = new Rfc2898DeriveBytes(password, SALT_SIZE, ITERATIONS))
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{
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var authenticationSalt = authenticationGenerator.Salt;
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var authenticationKey = authenticationGenerator.GetBytes(KEY_SIZE);
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var encryptionSalt = encryptionGenerator.Salt;
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var encryptionKey = encryptionGenerator.GetBytes(KEY_SIZE);
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return (authenticationKey, authenticationSalt, encryptionKey, encryptionSalt);
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}
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}
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private (byte[] originalHmac, byte[] computedHmac) GenerateHmacForDecryption(byte[] authenticationKey, Stream data)
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{
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logger.Debug("Generating HMACs for authentication...");
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using (var algorithm = new HMACSHA256(authenticationKey))
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{
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var originalHmac = new byte[algorithm.HashSize / 8];
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var hashStream = new SubStream(data, 0, data.Length - originalHmac.Length);
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var computedHmac = algorithm.ComputeHash(hashStream);
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data.Seek(-originalHmac.Length, SeekOrigin.End);
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data.Read(originalHmac, 0, originalHmac.Length);
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return (originalHmac, computedHmac);
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}
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}
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private byte[] GenerateHmacForEncryption(byte[] authenticationKey, Stream data)
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{
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data.Seek(0, SeekOrigin.Begin);
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logger.Debug("Generating HMAC for authentication...");
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using (var algorithm = new HMACSHA256(authenticationKey))
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{
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return algorithm.ComputeHash(data);
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}
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}
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private LoadStatus FailForInvalidHmac()
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{
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logger.Debug($"The authentication failed due to an invalid password or corrupted data!");
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return LoadStatus.PasswordNeeded;
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}
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private Stream Decrypt(Stream data, byte[] encryptionKey, int hmacLength)
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{
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var initializationVector = new byte[BLOCK_SIZE];
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data.Seek(HEADER_SIZE + 2 * SALT_SIZE, SeekOrigin.Begin);
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data.Read(initializationVector, 0, BLOCK_SIZE);
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var decryptedData = new MemoryStream();
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var encryptedData = new SubStream(data, data.Position, data.Length - data.Position - hmacLength);
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logger.Debug("Decrypting data...");
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using (var algorithm = new AesManaged { KeySize = KEY_SIZE * 8, BlockSize = BLOCK_SIZE * 8, Mode = CipherMode.CBC, Padding = PaddingMode.PKCS7 })
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using (var decryptor = algorithm.CreateDecryptor(encryptionKey, initializationVector))
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using (var cryptoStream = new CryptoStream(encryptedData, decryptor, CryptoStreamMode.Read))
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{
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cryptoStream.CopyTo(decryptedData);
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}
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return decryptedData;
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}
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private Stream Encrypt(Stream data, byte[] encryptionKey, out byte[] initializationVector)
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{
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var encryptedData = new MemoryStream();
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logger.Debug("Encrypting data...");
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using (var algorithm = new AesManaged { KeySize = KEY_SIZE * 8, BlockSize = BLOCK_SIZE * 8, Mode = CipherMode.CBC, Padding = PaddingMode.PKCS7 })
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{
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algorithm.GenerateIV();
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data.Seek(0, SeekOrigin.Begin);
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initializationVector = algorithm.IV;
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using (var encryptor = algorithm.CreateEncryptor(encryptionKey, initializationVector))
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using (var cryptoStream = new CryptoStream(data, encryptor, CryptoStreamMode.Read))
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{
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cryptoStream.CopyTo(encryptedData);
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}
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return encryptedData;
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}
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}
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private Stream WriteEncryptionParameters(byte[] authKey, byte[] authSalt, byte[] encrSalt, byte[] initVector, Stream encryptedData)
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{
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var data = new MemoryStream();
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var header = new byte[] { VERSION, OPTIONS };
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logger.Debug("Writing encryption parameters...");
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data.Write(header, 0, header.Length);
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data.Write(encrSalt, 0, encrSalt.Length);
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data.Write(authSalt, 0, authSalt.Length);
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data.Write(initVector, 0, initVector.Length);
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encryptedData.Seek(0, SeekOrigin.Begin);
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encryptedData.CopyTo(data);
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var hmac = GenerateHmacForEncryption(authKey, data);
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data.Seek(0, SeekOrigin.End);
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data.Write(hmac, 0, hmac.Length);
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return data;
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}
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}
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}
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