/// ---------------------------------------------------------------------------------------- /// <summary> /// Encrypt preferences using a password /// </summary> /// ---------------------------------------------------------------------------------------- // Encrypt preferences using a password public static byte[] EncryptDataUsingPassword(byte[] data, string password, bool passwordIsHash, SEBSettings.sebConfigPurposes configPurpose) { string prefixString; // Check if .seb file should start exam or configure client if (configPurpose == SEBSettings.sebConfigPurposes.sebConfigPurposeStartingExam) { // prefix string for starting exam: normal password will be prompted prefixString = PASSWORD_MODE; } else { // prefix string for configuring client: configuring password will either be hashed admin pw on client // or if no admin pw on client set: empty pw prefixString = PASSWORD_CONFIGURING_CLIENT_MODE; if (!String.IsNullOrEmpty(password) && !passwordIsHash) { //empty password means no admin pw on clients and should not be hashed //or we got already a hashed admin pw as settings pw, then we don't hash again password = SEBProtectionController.ComputePasswordHash(password); } } byte[] encryptedData = SEBProtectionController.EncryptDataWithPassword(data, password); // Create byte array large enough to hold prefix and data byte[] encryptedSebData = new byte[encryptedData.Length + PREFIX_LENGTH]; Buffer.BlockCopy(Encoding.UTF8.GetBytes(prefixString), 0, encryptedSebData, 0, PREFIX_LENGTH); Buffer.BlockCopy(encryptedData, 0, encryptedSebData, PREFIX_LENGTH, encryptedData.Length); return(encryptedSebData); }
/// ---------------------------------------------------------------------------------------- /// <summary> /// Ask user to enter password and compare it to the passed (hashed) password string /// Returns true if correct password was entered /// </summary> /// ---------------------------------------------------------------------------------------- private static bool askForPasswordAndCompareToHashedPassword(string sebFileHashedAdminPassword, bool forEditing) { // Check if there wasn't a hashed password (= empty password) if (sebFileHashedAdminPassword.Length == 0) { return(true); } // We have to ask for the SEB administrator password used in the settings // and allow opening settings only if the user enters the right one // Allow up to 5 attempts for entering admin password int i = 5; string password = null; string hashedPassword; string enterPasswordString = SEBUIStrings.enterAdminPasswordRequired; bool passwordsMatch; do { i--; // Prompt for password password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.loadingSettings + (String.IsNullOrEmpty(SEBClientInfo.LoadingSettingsFileName) ? "" : ": " + SEBClientInfo.LoadingSettingsFileName), enterPasswordString); // If cancel was pressed, abort if (password == null) { return(false); } if (password.Length == 0) { hashedPassword = ""; } else { hashedPassword = SEBProtectionController.ComputePasswordHash(password); } passwordsMatch = (String.Compare(hashedPassword, sebFileHashedAdminPassword, StringComparison.OrdinalIgnoreCase) == 0); // in case we get an error we allow the user to try it again enterPasswordString = SEBUIStrings.enterAdminPasswordRequiredAgain; } while ((password == null || !passwordsMatch) && i > 0); if (!passwordsMatch) { //wrong password entered in 5th try: stop reading .seb file MessageBox.Show(SEBUIStrings.loadingSettingsFailed, SEBUIStrings.loadingSettingsFailedWrongAdminPwd, MessageBoxButtons.OK, MessageBoxIcon.Error); return(false); } // Right password entered return(passwordsMatch); }
/// ---------------------------------------------------------------------------------------- /// <summary> /// Helper method which fetches the public key hash from a byte array, /// retrieves the according cryptographic identity from the certificate store /// and returns the decrypted bytes /// </summary> /// ---------------------------------------------------------------------------------------- private static byte[] DecryptDataWithPublicKeyHashPrefix(byte[] sebData, bool usingSymmetricKey, bool forEditing, ref X509Certificate2 sebFileCertificateRef) { // Get 20 bytes public key hash prefix // and remaining data with the prefix stripped byte[] publicKeyHash = GetPrefixDataFromData(ref sebData, PUBLIC_KEY_HASH_LENGTH); X509Certificate2 certificateRef = SEBProtectionController.GetCertificateFromStore(publicKeyHash); if (certificateRef == null) { MessageBox.Show(SEBUIStrings.errorDecryptingSettings, SEBUIStrings.certificateNotFoundInStore, MessageBoxButtons.OK, MessageBoxIcon.Error); return(null); } // If these settings are being decrypted for editing, we will return the decryption certificate reference // in the variable which was passed as reference when calling this method if (forEditing) { sebFileCertificateRef = certificateRef; } // Are we using the new identity certificate decryption with a symmetric key? if (usingSymmetricKey) { // Get length of the encrypted symmetric key Int32 encryptedSymmetricKeyLength = BitConverter.ToInt32(GetPrefixDataFromData(ref sebData, sizeof(Int32)), 0); // Get encrypted symmetric key byte[] encryptedSymmetricKey = GetPrefixDataFromData(ref sebData, encryptedSymmetricKeyLength); // Decrypt symmetric key byte[] symmetricKey = SEBProtectionController.DecryptDataWithCertificate(encryptedSymmetricKey, certificateRef); if (symmetricKey == null) { return(null); } string symmetricKeyString = Convert.ToBase64String(symmetricKey); // Decrypt config file data using the symmetric key as password sebData = SEBProtectionController.DecryptDataWithPassword(sebData, symmetricKeyString); } else { sebData = SEBProtectionController.DecryptDataWithCertificate(sebData, certificateRef); } return(sebData); }
/// ---------------------------------------------------------------------------------------- /// <summary> /// Encrypt preferences using a certificate /// </summary> /// ---------------------------------------------------------------------------------------- public static byte[] EncryptDataUsingIdentity(byte[] data, X509Certificate2 certificateRef, bool useAsymmetricOnlyEncryption) { // Get public key hash from selected identity's certificate string prefixString; byte[] publicKeyHash = SEBProtectionController.GetPublicKeyHashFromCertificate(certificateRef); byte[] encryptedData; byte[] encryptedKeyLengthBytes = new byte[0]; byte[] encryptedKey = new byte[0]; byte[] encryptedSEBConfigData; if (!useAsymmetricOnlyEncryption) { prefixString = PUBLIC_SYMMETRIC_KEY_MODE; // For new asymmetric/symmetric encryption create a random symmetric key byte[] symmetricKey = AESThenHMAC.NewKey(); string symmetricKeyString = Convert.ToBase64String(symmetricKey); // Encrypt the symmetric key using the identity certificate encryptedKey = SEBProtectionController.EncryptDataWithCertificate(symmetricKey, certificateRef); // Get length of the encrypted key encryptedKeyLengthBytes = BitConverter.GetBytes(encryptedKey.Length); //encrypt data using symmetric key encryptedData = SEBProtectionController.EncryptDataWithPassword(data, symmetricKeyString); } else { prefixString = PUBLIC_KEY_HASH_MODE; //encrypt data using public key encryptedData = SEBProtectionController.EncryptDataWithCertificate(data, certificateRef); } // Create byte array large enough to hold prefix, public key hash, length of and encrypted symmetric key plus encrypted data encryptedSEBConfigData = new byte[PREFIX_LENGTH + publicKeyHash.Length + encryptedKeyLengthBytes.Length + encryptedKey.Length + encryptedData.Length]; int destinationOffset = 0; // Copy prefix indicating data has been encrypted with a public key identified by hash into out data Buffer.BlockCopy(Encoding.UTF8.GetBytes(prefixString), 0, encryptedSEBConfigData, destinationOffset, PREFIX_LENGTH); destinationOffset += PREFIX_LENGTH; // Copy public key hash to out data Buffer.BlockCopy(publicKeyHash, 0, encryptedSEBConfigData, destinationOffset, publicKeyHash.Length); destinationOffset += publicKeyHash.Length; // Copy length of encrypted symmetric key to out data Buffer.BlockCopy(encryptedKeyLengthBytes, 0, encryptedSEBConfigData, destinationOffset, encryptedKeyLengthBytes.Length); destinationOffset += encryptedKeyLengthBytes.Length; // Copy encrypted symmetric key to out data Buffer.BlockCopy(encryptedKey, 0, encryptedSEBConfigData, destinationOffset, encryptedKey.Length); destinationOffset += encryptedKey.Length; // Copy encrypted data to out data Buffer.BlockCopy(encryptedData, 0, encryptedSEBConfigData, destinationOffset, encryptedData.Length); return(encryptedSEBConfigData); }
/// ---------------------------------------------------------------------------------------- /// <summary> /// Decrypt and deserialize SEB settings /// When forEditing = true, then the decrypting password the user entered and/or /// certificate reference found in the .seb file is returned /// </summary> /// ---------------------------------------------------------------------------------------- public static DictObj DecryptSEBSettings(byte[] sebData, bool forEditing, ref string sebFilePassword, ref bool passwordIsHash, ref X509Certificate2 sebFileCertificateRef, bool suppressFileFormatError = false) { // Ungzip the .seb (according to specification >= v14) source data byte[] unzippedSebData = GZipByte.Decompress(sebData); // if unzipped data is not null, then unzipping worked, we use unzipped data // if unzipped data is null, then the source data may be an uncompressed .seb file, we proceed with it if (unzippedSebData != null) { sebData = unzippedSebData; } string prefixString; // save the data including the first 4 bytes for the case that it's acutally an unencrypted XML plist byte[] sebDataUnencrypted = sebData.Clone() as byte[]; // Get 4-char prefix prefixString = GetPrefixStringFromData(ref sebData); //// Check prefix identifying encryption modes /// Check for new Multipart and Custom headers // Multipart Config File: The first part containts the regular SEB key/value settings // following parts can contain additional resources. An updated SEB version will be // able to read and process those parts sequentially as a stream. // Therefore potentially large additional resources won't have to be loaded into memory at once if (prefixString.CompareTo(MULTIPART_MODE) == 0) { // Skip the Multipart Config File header byte[] multipartConfigLengthData = GetPrefixDataFromData(ref sebData, MULTIPART_LENGTH); long multipartConfigLength = BitConverter.ToInt64(multipartConfigLengthData, 0); Logger.AddInformation("Multipart Config File, first part (settings) length: " + multipartConfigLength); try { Logger.AddInformation("Cropping config file, as this SEB version cannot process additional parts of multipart config files."); byte[] dataFirstPart = new byte[sebData.Length - multipartConfigLength]; Buffer.BlockCopy(sebData, 0, dataFirstPart, 0, dataFirstPart.Length); sebData = dataFirstPart; } catch (Exception ex) { Logger.AddError("Error while cropping config file", null, ex, ex.Message); } } // Custom Header: Containts a 32 bit value for the length of the header // followed by the custom header information. After the header, regular // SEB config file data follows if (prefixString.CompareTo(CUSTOM_HEADER_MODE) == 0) { // Skip the Custom Header byte[] customHeaderLengthData = GetPrefixDataFromData(ref sebData, CUSTOMHEADER_LENGTH); int customHeaderLength = BitConverter.ToInt32(customHeaderLengthData, 0); Logger.AddInformation("Custom Config File Header length: " + customHeaderLength); try { Logger.AddInformation("Removing custom header from config file data. This SEB version cannot process this header type and will ignore it."); byte[] customHeaderData = GetPrefixDataFromData(ref sebData, customHeaderLength); Logger.AddInformation("Custom header data: " + customHeaderData); } catch (Exception ex) { Logger.AddError("Error while removing custom header from config file data", null, ex, ex.Message); } } // Prefix = pksh ("Public-Symmetric Key Hash") ? if (prefixString.CompareTo(PUBLIC_SYMMETRIC_KEY_MODE) == 0) { // Decrypt with cryptographic identity/private and symmetric key sebData = DecryptDataWithPublicKeyHashPrefix(sebData, true, forEditing, ref sebFileCertificateRef); if (sebData == null) { return(null); } // Get 4-char prefix again // and remaining data without prefix, which is either plain or still encoded with password prefixString = GetPrefixStringFromData(ref sebData); } // Prefix = pkhs ("Public Key Hash") ? if (prefixString.CompareTo(PUBLIC_KEY_HASH_MODE) == 0) { // Decrypt with cryptographic identity/private key sebData = DecryptDataWithPublicKeyHashPrefix(sebData, false, forEditing, ref sebFileCertificateRef); if (sebData == null) { return(null); } // Get 4-char prefix again // and remaining data without prefix, which is either plain or still encoded with password prefixString = GetPrefixStringFromData(ref sebData); } // Prefix = pswd ("Password") ? if (prefixString.CompareTo(PASSWORD_MODE) == 0) { // Decrypt with password // if the user enters the right one byte[] sebDataDecrypted = null; string password; // Allow up to 5 attempts for entering decoding password string enterPasswordString = SEBUIStrings.enterPassword; int i = 5; do { i--; // Prompt for password password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.loadingSettings, enterPasswordString); if (password == null) { return(null); } //error = nil; sebDataDecrypted = SEBProtectionController.DecryptDataWithPassword(sebData, password); enterPasswordString = SEBUIStrings.enterPasswordAgain; // in case we get an error we allow the user to try it again } while ((sebDataDecrypted == null) && i > 0); if (sebDataDecrypted == null) { //wrong password entered in 5th try: stop reading .seb file MessageBox.Show(SEBUIStrings.decryptingSettingsFailed, SEBUIStrings.decryptingSettingsFailedReason, MessageBoxButtons.OK, MessageBoxIcon.Error); return(null); } sebData = sebDataDecrypted; // If these settings are being decrypted for editing, we return the decryption password if (forEditing) { sebFilePassword = password; } } else { // Prefix = pwcc ("Password Configuring Client") ? if (prefixString.CompareTo(PASSWORD_CONFIGURING_CLIENT_MODE) == 0) { // Decrypt with password and configure local client settings // and quit afterwards, returning if reading the .seb file was successfull DictObj sebSettings = DecryptDataWithPasswordForConfiguringClient(sebData, forEditing, ref sebFilePassword, ref passwordIsHash); return(sebSettings); } else { // Prefix = plnd ("Plain Data") ? if (prefixString.CompareTo(PLAIN_DATA_MODE) != 0) { // No valid 4-char prefix was found in the .seb file // Check if .seb file is unencrypted if (prefixString.CompareTo(UNENCRYPTED_MODE) == 0) { // .seb file seems to be an unencrypted XML plist // get the original data including the first 4 bytes sebData = sebDataUnencrypted; } else { // No valid prefix and no unencrypted file with valid header // cancel reading .seb file if (!suppressFileFormatError) { MessageBox.Show(SEBUIStrings.settingsNotUsable, SEBUIStrings.settingsNotUsableReason, MessageBoxButtons.OK, MessageBoxIcon.Error); } return(null); } } } } // If we don't deal with an unencrypted seb file // ungzip the .seb (according to specification >= v14) decrypted serialized XML plist data if (prefixString.CompareTo(UNENCRYPTED_MODE) != 0) { sebData = GZipByte.Decompress(sebData); } // Get preferences dictionary from decrypted data DictObj sebPreferencesDict = GetPreferencesDictFromConfigData(sebData, forEditing); // If we didn't get a preferences dict back, we abort reading settings if (sebPreferencesDict == null) { return(null); } // We need to set the right value for the key sebConfigPurpose to know later where to store the new settings sebPreferencesDict[SEBSettings.KeySebConfigPurpose] = (int)SEBSettings.sebConfigPurposes.sebConfigPurposeStartingExam; // Reading preferences was successful! return(sebPreferencesDict); }
/// ---------------------------------------------------------------------------------------- /// <summary> /// Helper method which decrypts the byte array using an empty password, /// or the administrator password currently set in SEB /// or asks for the password used for encrypting this SEB file /// for configuring the client /// </summary> /// ---------------------------------------------------------------------------------------- private static DictObj DecryptDataWithPasswordForConfiguringClient(byte[] sebData, bool forEditing, ref string sebFilePassword, ref bool passwordIsHash) { passwordIsHash = false; string password; // First try to decrypt with the current admin password // get admin password hash string hashedAdminPassword = (string)SEBSettings.valueForDictionaryKey(SEBSettings.settingsCurrent, SEBSettings.KeyHashedAdminPassword); if (hashedAdminPassword == null) { hashedAdminPassword = ""; } // We use always uppercase letters in the base16 hashed admin password used for encrypting hashedAdminPassword = hashedAdminPassword.ToUpper(); DictObj sebPreferencesDict = null; byte[] decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, hashedAdminPassword); if (decryptedSebData == null) { // If decryption with admin password didn't work, try it with an empty password decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, ""); if (decryptedSebData == null) { // If decryption with empty and admin password didn't work, ask for the password the .seb file was encrypted with // Allow up to 5 attempts for entering decoding password int i = 5; password = null; string enterPasswordString = SEBUIStrings.enterEncryptionPassword; do { i--; // Prompt for password password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.reconfiguringLocalSettings, enterPasswordString); // If cancel was pressed, abort if (password == null) { return(null); } string hashedPassword = SEBProtectionController.ComputePasswordHash(password); // we try to decrypt with the hashed password decryptedSebData = SEBProtectionController.DecryptDataWithPassword(sebData, hashedPassword); // in case we get an error we allow the user to try it again enterPasswordString = SEBUIStrings.enterEncryptionPasswordAgain; } while (decryptedSebData == null && i > 0); if (decryptedSebData == null) { //wrong password entered in 5th try: stop reading .seb file MessageBox.Show(SEBUIStrings.reconfiguringLocalSettingsFailed, SEBUIStrings.reconfiguringLocalSettingsFailedWrongPassword, MessageBoxButtons.OK, MessageBoxIcon.Error); return(null); } else { // Decrypting with entered password worked: We save it for returning it later if (forEditing) { sebFilePassword = password; } } } } else { //decrypting with hashedAdminPassword worked: we save it for returning as decryption password sebFilePassword = hashedAdminPassword; // identify that password as hash passwordIsHash = true; } /// Decryption worked // Ungzip the .seb (according to specification >= v14) decrypted serialized XML plist data decryptedSebData = GZipByte.Decompress(decryptedSebData); // Check if the openend reconfiguring seb file has the same admin password inside like the current one try { sebPreferencesDict = (DictObj)Plist.readPlist(decryptedSebData); } catch (Exception readPlistException) { // Error when deserializing the decrypted configuration data // We abort reading the new settings here MessageBox.Show(SEBUIStrings.loadingSettingsFailed, SEBUIStrings.loadingSettingsFailedReason, MessageBoxButtons.OK, MessageBoxIcon.Error); Console.WriteLine(readPlistException.Message); return(null); } // Get the admin password set in these settings string sebFileHashedAdminPassword = (string)SEBSettings.valueForDictionaryKey(sebPreferencesDict, SEBSettings.KeyHashedAdminPassword); if (sebFileHashedAdminPassword == null) { sebFileHashedAdminPassword = ""; } // Has the SEB config file the same admin password inside as the current settings have? if (String.Compare(hashedAdminPassword, sebFileHashedAdminPassword, StringComparison.OrdinalIgnoreCase) != 0) { //No: The admin password inside the .seb file wasn't the same as the current one if (forEditing) { // If the file is openend for editing (and not to reconfigure SEB) // we have to ask the user for the admin password inside the file if (!askForPasswordAndCompareToHashedPassword(sebFileHashedAdminPassword, forEditing)) { // If the user didn't enter the right password we abort return(null); } } else { // The file was actually opened for reconfiguring the SEB client: // we have to ask for the current admin password and // allow reconfiguring only if the user enters the right one // We don't check this for the case the current admin password was used to encrypt the new settings // In this case there can be a new admin pw defined in the new settings and users don't need to enter the old one if (passwordIsHash == false && hashedAdminPassword.Length > 0) { // Allow up to 5 attempts for entering current admin password int i = 5; password = null; string hashedPassword; string enterPasswordString = SEBUIStrings.enterCurrentAdminPwdForReconfiguring; bool passwordsMatch; do { i--; // Prompt for password password = SebPasswordDialogForm.ShowPasswordDialogForm(SEBUIStrings.reconfiguringLocalSettings, enterPasswordString); // If cancel was pressed, abort if (password == null) { return(null); } if (password.Length == 0) { hashedPassword = ""; } else { hashedPassword = SEBProtectionController.ComputePasswordHash(password); } passwordsMatch = (String.Compare(hashedPassword, hashedAdminPassword, StringComparison.OrdinalIgnoreCase) == 0); // in case we get an error we allow the user to try it again enterPasswordString = SEBUIStrings.enterCurrentAdminPwdForReconfiguringAgain; } while (!passwordsMatch && i > 0); if (!passwordsMatch) { //wrong password entered in 5th try: stop reading .seb file MessageBox.Show(SEBUIStrings.reconfiguringLocalSettingsFailed, SEBUIStrings.reconfiguringLocalSettingsFailedWrongCurrentAdminPwd, MessageBoxButtons.OK, MessageBoxIcon.Error); return(null); } } } } // We need to set the right value for the key sebConfigPurpose to know later where to store the new settings sebPreferencesDict[SEBSettings.KeySebConfigPurpose] = (int)SEBSettings.sebConfigPurposes.sebConfigPurposeConfiguringClient; // Reading preferences was successful! return(sebPreferencesDict); }