Fortress Mail v2.52 User Guide
Contents
Known
Answer Test Results for Serpent and Rijndael
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Introduction
Fortress Mail is an encrypting email client program that uses your existing email program (such as Outlook, Outlook Express or Eudora) to send and receive messages. The messages and attachments are encrypted automatically using your selected encryption algorithm and then sent via your standard email program.
Fortress Mail uses a simple password based encryption / decryption system using state of the art encryption algorithms including modes compatible with the U.S. Advanced Encryption Standard (AES). Fortress Mail does not require you to have a digital certificate.
The program uses an interface called MAPI to connect to your default email program and uses it to send and receive emails. Outgoing emails are encrypted and then queued to the Outbox of your default email program. Incoming email is read from the standard Inbox of your default email program.
Fortress Mail emails are stored in their encrypted form and must be decoded with the correct password each time they are opened.
Programs that support MAPI include Outlook, Outlook express and Eudora.
Fortress Mail v2.0 will read Fortress Mail v1.xx emails but cannot authenticate either contents or sender since the earlier protocol does not contain this information
Note that for Fortress Mail to work:
(1) You must have MAPI installed on your operating system (Windows 98/Me/NT4/2000/XP should already have MAPI installed, you will probably need to install it for Windows 95).
(2) Your default email program must at least support Simple MAPI for Fortress Mail to work (Extended MAPI necessary for Sent Items View).
(3) For RC4 and HS1 encryption modes you will need to have the Microsoft Enhanced Cryptographic Provider installed (available from the Microsoft Web Site).
Fortress Mail has been tested with Outlook 97/2000, Outlook Express 4/5.5/6 and Eudora 5.1 under Windows 95/Me/NT4/2000/XP.
Fortress Mail will only work under Microsoft Windows 95/98/Me/NT4/2000/XP which must have MAPI installed.
For the Trial version only 100 characters and NO attachments may be sent although the receive capabilities of the Full version should be available.
Unlocking Fortress Mail
To unlock Fortress Mail and enable full send capability you will need to provide your Application ID number which is given in the Fortress Mail “About Box”:
To register go to www.fortressmail.net and follow the instructions.
Encryption
Fortress Mail provides a number of encryption algorithms for you to use. They are:
(1) RC4 with a 128 bit key. This is a strong stream cipher provided by the Microsoft Enhanced Cryptographic Provider.
(2) Serpent is a strong block cipher designed by Ross Anderson, Eli Biham and Lars Knudsen and recently came second out of 5 finalists for the U.S. Advanced Encryption Standard (AES). This program uses an independent implementation of the algorithm based on original code developed by Dr Brian Gladman. The modes offered by Fortress Mail are 128, 192 and 256 bit key sizes for 128 bit blocks with CBC (cipher block chaining). The use of CBC should eliminate repeated block patterns with repetitive data.
(3) Rijndael is a strong block cipher developed by Joan Daemen and Vincent Rijmen and is the chosen cipher for the U.S. Advanced Encryption Standard (AES). This program uses an independent implementation of the algorithm based on original code developed by Dr Brian Gladman. The modes offered by Fortress Mail are 128, 192 and 256 bit key sizes for 128 bit blocks with CBC. These modes are compatible with the AES.
(4) HS1 pre-encrypts the message using RC4 with a 128 bit key and then encrypts this cipher text using Rijndael with a 256 bit key. This is a stronger alternative to using CBC (or CFB) to eliminate repeated block patterns with repetitive data.
These algorithms use the same key (based on the supplied password) for encryption and decryption and are thus known as symmetric key ciphers. Symmetric key encryption is generally much stronger (for the same key size) and faster than public key encryption, which is not supported by this version of Fortress Mail.
Fortress Mail also provides a mechanism for checking that the contents of the message have not been altered or damaged after being sent, as well as tagging each email with an ID unique* to the originating installation of the program. See the Message Authentication section for more details.
* The odds of another installation of Fortress Mail having the same System Authentication ID as you are 1 in 3.4x1038 (1 in 3.4 times 10 raised to the 38th power). An installation is all copies of Fortress Mail on a single computer.
Note that Fortress Mail encrypts the text of the message
body and any files attached to the email (“attachments”), it does not encrypt
the subject field (denoted “Re:” in Fortress Mail).
Rijndael and Serpent both have a number of web pages dedicated to them. For example the Rijndael Home Page and the Serpent Home Page.
Starting Fortress Mail
To start Fortress Mail if not already running just click on the desktop shortcut or launch from the Start Menu.
If you are running Outlook you will get a profile selection screen and you should select the desired profile (this will normally be “Microsoft Outlook” but could differ depending on your setup). You may also be required to enter the password for that profile depending on your system setup. To log off use the “Logoff” command in the “File” menu, you may then log back on to the same profile or a different profile by using the “Logon” command from the “File” menu. Note that exiting the program automatically logs you off.
For Outlook Express and Eudora you will not get a profile screen although Eudora will start up if not already running.
Possible Problems:
If you see no entries in the Inbox there could be several possible explanations.
(1) All Fortress Mail emails start their subject lines with FORTRESS: and only emails with subject lines beginning this way will be displayed.
(2) Eudora is set as you default email client and is not running. Start Eudora and see if this solves the problem.
(3) You do not have a MAPI compatible email program set as the default email program. Start the Control panel Internet Options program and use the Programs tab to select a compatible email program.
If you get an Ordinal xx not found error with Eudora.
(1) If Eudora is the default Email program turn OFF the Eudora MAPI server.
Sending an Encrypted Email
Start Fortress Mail if not already running.
Select “Send Coded Mail…” from the “Mail” menu. You will see a dialog like this:
(1) In the Pw: box enter a password. This will be the password for the email. ONLY SOMEONE WHO KNOWS THE PASSWORD WILL BE ABLE TO READ THE MESSAGE OR DECRYPT ANY ATTACHMENTS SO ENSURE THAT THE RECIPIENT KNOWS THE PASSWORD.
(2) A note on passwords: Whilst the password can be any length (up to the maximum key size) you are advised to use at least 8 characters and preferably more than 12. The longer, more random and harder to guess, the better.
(3) In the To: box enter the email address of the recipient(s).
(4) In the Re: box enter the subject of the email. Note that you should not manually type FORTRESS: since this will be added automatically.
(5) If you leave “Indicate algorithm in subject line” the algorithm used to encode the message and attachments will be automatically inserted into the subject line (e.g. [Ser 128] for Serpent with a 128 bit keysize). If present this will be used by the recipients copy of Fortress Mail to automatically apply the correct algorithm to the decryption process.
(6) If you tick the “Encode files as text” box then any attachments will be encoded as hexadecimal text. This will significantly increase the file size(s) but may be useful if you are having problems transmitting attachments as binary.
(7) Enter your message in the large box at the bottom of the dialog.
(8) To attach a file press the “Attach” button and select the desired file. Repeat to select additional files.
(9) Press the “Send” button to send the email.
If you get a “Failed to acquire context (RC4)” error then there is a problem with accessing the Microsoft Enhanced Cryptographic Provider. The most likely reason for this is that it is not installed in which case you should see the Microsoft Web Site for download instructions.
Note on Eudora.
If Eudora is set as your default email program and the Fortress Mail appears to hang after you hit “Send” then Eudora is requesting the password to your email account. Click on the Eudora program to bring it into focus and enter your password in the dialog box.
Reading an Encrypted Email
To read an incoming Fortress Mail email.
(1) Select “Read Mail…” from the Mail menu.
(2) Double click on the desired message or highlight it with a mouse click and then click the Read button.
(3) You will see a Read Message Dialog like this:
To decrypt the message enter the password (case sensitive) in the Pw: box and press the Decode button. If you get a decode successful message then you may read and save the decoded message. Any attachments will automatically decrypt when saved.
It is important to note that the message is only decrypted
whilst the “Read Message” dialog is open. Messages are stored in encrypted
form and must be decrypted each time they are opened.
If you get an incorrect password message quit the dialog if you wish to retry.
If you get a “Failed to acquire context (RC4)” error then there is a problem with accessing the Microsoft Enhanced Cryptographic Provider. The most likely reason for this is that it is not installed in which case you should see the Microsoft Web Site for download instructions.
Each message starts with a validation block. If this is the only text in the message body then no text will be displayed when decoded (this may occur, for example, if an attachment has been sent with no text in the accompanying message).
Note that if the algorithm is not shown in the subject field then Fortress Mail will try to decrypt the message using the default algorithm and key size (shown on the main screen of the program). If these are incorrect then the password will not work even if correct.
Message Authentication
A Message Authentication Packet of variable length is sent as part of each email. This packet contains information about the email including the number and names of the attachments, message digests of encrypted components and data relating to the System Authentication ID of the copy of Fortress Mail used to send the message (note that the trial version of the software does not send a valid System Authentication ID - every trial version has the same ID: 3613E74A-BFF94BE4-2E75D279-A5184823 - although it will display that of incoming mail).
The Message Authentication Packet is separately encrypted
from the message body with an algorithm that may, or may not, be the same as
that of the message itself and uses a different (automatically generated)
password.
When you decrypt the email, the integrity of the original text message is checked and you are notified if the contents have changed. This includes the name(s) and number of attached file(s) although individual file integrity is checked when you save that particular attachment.
For example, if the attachment list had been changed you would get a message like the one below:
or if the message body has been corrupted:
The System Authentication ID of the originating copy of Fortress Mail is displayed at the bottom of the “Read Message” dialog, together with an “Owner of Sending System” field – which you can fill in as you build trust relationships. For example:
The System Authentication ID of your copy of Fortress Mail is shown at the bottom of the “About Fortress Mail” dialog.
Note that an Authentication Error message does not necessarily mean that the email has been deliberately tampered with.
The Authentication Database
Fortress Mail now allows you to optionally configure your own trust relationships by associating the System Authentication ID with a particular person or group. Sender details entered in the Authentication Database are stored in encrypted form.
If you wish to use the Authentication Database you can either use the default password (if you aren’t too worried about security) and database path (C:\SenderDB.fdb) in which case you can proceed to the section on “Adding or Editing Data” or you can configure your own password and path for the database file. To use your own password select “Manage Identities” from the Mail Menu to bring up the following dialog box:
Enter your own password in the “Change DB Password” field and tick the “Store Password” box if you want Fortress Mail to remember the password next time otherwise you will need to reenter the password every time you start up the software. Preferably use at least 8 characters and include numbers and/or other symbols such as $, the longer and harder to guess the password, the more secure your data will be.
To change the database file path enter your desired path in the “Database Path” field. Note that:
Fortress Mail will create the file
if necessary however the rest of the path must exist or entries will not be
written.
Although the Authentication
Database has been designed for personal use, it is possible to place the data
file on a shared drive and allow other users to access it over a network (a
common password would need to be agreed).
However, it was not designed as a multi-user database.
If you intend to store sender
password information in the database you should ensure that the database file
is suitably protected from unauthorized access, and a strong password is
applied to the database (12 or more characters, avoid real words or names and
include non-alphabetic characters such as numbers or symbols). Also note that
setting Fortress Mail to remember the database password could compromise
security if the computer were stolen or subject to unauthorized access and
suitable precautions should be taken.
Frequent backups are recommended.
Adding or Editing Data
This can be done in two ways:
1. When you have decoded an incoming email you can press the Add/Edit button at the bottom of the dialog and you will see a dialog like the one shown below:
Simply enter the details in the Sender Details box and press OK (entries limited to 256 characters). You can enter details for up to 1024 different System Authentication IDs.
2. To manually enter a System Authentication ID and associated sender details you can use the “Manage Identities” item in the “Mail” menu and type or paste in the new Authentication ID and details. You can also use this dialog to search for details associated with a given Authentication ID.
Miscellaneous
(1) To change the default algorithm select “Preferences…” from the “Mail” menu.
(2) To send an unencrypted email select “Send Normal Mail…” from the “Mail” menu and a standard mail dialog for your default email program will be displayed.
(3) The “Get Details…” item in the “Mail” menu displays a standard view onto the Address Book of the default email program.
Limits and Caveats
(1) Message text is limited to 32 Kilobytes.
(2) Attachment size may be limited by your default email program or service provider. Fortress Mail has been tested up to 875 K for a single attachment.
(3) Total email size (message + attachments) may be limited by your default email program or your service provider.
(4) For the Trial Version only 100 characters and NO attachments may be sent although full receive capabilities are available.
(5) Fortress Mail sends and receives via your default email program. Therefore messages are only sent or received when your default email program sends or receives.
(6) Eudora and Outlook Express only support the Simple MAPI interface therefore the Sent Items dialog box will not display mail sent via these applications.
(7) If the password field is left empty an algorithm dependent default password will be used.
(8) Temporary encrypted files are stored in a folder called “C:\FortressFiles” which can be deleted to release disk space when required (it will be recreated when needed by Fortress Mail).
(9) Occasionally Fortress Mail may not respond immediately. This is because it is waiting for a response from your default email program which may be busy, for example fetching or sending email.
(10) The “Sent Items” view only processes the first 500 items in your sent items folder (to prevent excessive delays possible with large numbers of sent items being checked and processed).
(11) In order to make Fortress mail as compatible as possible filenames will be reformatted so that:
1.
All filenames have an extension (.dat will be added if
no extension is present).
2.
If a filename is greater than 14 characters it will be
truncated to 10 characters+ 3 character extension
3.
A final
character of “_” will be added to the extension to avoid problems with
binary being treated as text by any program routing or storing the email.
4.
All spaces will be converted to “_”.
* Note that when saving an attachment the appended “_”
is removed from the suggested filename in the save dialog although you can, of
course, give the file a different name.
Known Answer Test Results for Serpent and Rijndael
The Fortress Mail installation includes two binary files called “Rijndael.kat” and “Serpent.kat” which contain 16 byte test blocks for checking the implementations of these two algorithms.
Rijndael.kat contains the pattern: 000102030405060708090A0B0C0D0E0F which corresponds to the test plain text pattern given in the Known Answer Test submission to the AES. The correct result for this pattern is given in the file ecb_iv.txt generated by the reference code which may be downloaded from the AES web site by clicking here. The results files produced by this code, including ecb_iv.txt, may also be downloaded from the AES web site by clicking here.
Serpent.kat contains the pattern: 0123456789ABCDEFFEDCBA9876543210 which corresponds to one of the test plain text patterns given in the Known Answer Test submission to the AES. The correct result for this pattern is given in the file ecb_iv.txt generated by the reference code which may be downloaded from the Serpent home page by clicking here. (Note the Serpent submission contains several plain text -> cipher text results).
To view the cipher text generated by Fortress from these patterns you should select the desired algorithm and key size and select “Send Coded Mail..” from the “Mail” menu. Leave the password field blank and tick “Encode files as text”. Attach the relevant file and send the mail to yourself. An encrypted file called <filename>xxxxxxxx.kat_.sly (where <filename> is either Serpent or Rijndael and xxxxxxxx corresponds to a variable number numerical digits) should be created in “C:\FortressFiles”. Open the file with notepad, ignore the first 16 characters which are a file information block (in this case 1000000000000016) and check the remaining hexadecimal text against that generated by the reference code.
Note that due to the CBC processing added to these algorithms only the first block is untouched. Subsequent blocks will be subject to the CBC process.
Copyright © 2002 Dr David J Reynolds
RC4 is a registered trademark of RSA Data Security, Inc. Other product or company names may be trademarks of their respective owners.
Last revised: March 17th, 2003