CCrypt 2.61
(GPL Free Software)

© 1999-2003 Michael J. McCollister

E-Mail: Ccrypt@MikeMcCollister.com
Web Page: MikeMcCollister.com/palm/

© 1997-2000 James Aspnes

E-Mail: aspnes@cs.yale.edu
Web Page: www.cs.yale.edu/~aspnes/pilot/

Forward

CCrypt is a simple encryption program for a Palm OS device.

Contents of This Document

  1. Warning
  2. Installation
  3. System Requirements
  4. Usage
  5. Encryption Method
  6. Error Messages
  7. Weaknesses
  8. Backwards Compatibility
  9. Bugs
  10. Version History
  11. Copying
  12. Disclaimers

I. Warning

II. Installation

Installation of CCrypt is just like any other Palm program.

IMPORTANT: Be sure to see section on backwards compatibility.

III. System Requirements

Requires Palm OS 2.0 or greater. 17 Kbytes of free memory on the Palm is required.

IV. Usage

Encryption

To encrypt, enter a pass phrase (up to 64 characters) in the field marked "Key" and the plain-text in the large unmarked field. Selecting the "Mask" checkbox will hide the current key. Selecting "ASCII Armor" will ASCII armor the clipboard data (see ASCII Armoring below). The menu option "Encrypt to Clipboard" and the "Encrypt" button will encrypt the plain-text using the key and leave the ciphertext in the clipboard. The ciphertext can then be pasted into memos, address book entries, etc.

Decryption

To decrypt, copy a ciphertext to the clipboard, start CCrypt, enter the pass phrase in the key field, and execute the menu option "Decrypt Clipboard" or the "Decrypt" button. The decrypted string will be displayed in the main field. You can scroll up or down with the hardware scroll buttons.

Note: Starting with version 2.0.0, it is OK for the ciphertext to be embedded in other text; CCrypt will ignore the extraneous stuff when decrypting. This feature can be handy if you want to be able to use "Select All" and "Copy" to fetch a memo with encrypted content but an unencrypted title. This feature only works with unarmored data.

ASCII Armoring

The ASCII armor command will replace the data you just encrypted with an "ASCII armored" version. This consists of one or more words starting with "arQx". The advantage of ASCII armoring is that it may be easier to mail to people, copy into programs not on your Palm, use in Palm programs that filter out non-ASCII values, and so forth. The Decrypt command will assume that any string starting with "arQx" is ASCII armored, and will unarmor it before decrypting.

Clear Key & Data

All data is cleared on exit and from CCrypt, when the power is turned off or when the "Clear Key & data" menu option is chosen. The user is also asked whether the clipboard should be cleared as well. The clipboard is not cleared when the user exits the program or when the device is turned off.

V. Encryption Method

Data is encrypted using IDEA, a strong 128-bit encryption algorithm.

Encryption proceeds in several steps:

  1. The 4-byte return value of TimGetSeconds() is prepended to the plain-text. This keeps the same plain-text from encrypting to the same ciphertext twice.
  2. The resulting text is padded with nulls to a multiple of 8 bytes.
  3. This padded text is encrypted using IDEA in cipher block chaining mode.
  4. The ciphertext is bounded by a 2-byte header and footer, escaped to eliminate nulls, and copied to the clipboard.

Decryption reverses these steps.

VI. Error Messages

Encryption can fail if escaping and padding results in a ciphertext too big for the clipboard limit. Encrypting generally expands text by about 0.7%.

Armoring can fail if the resulting text is too big for the clipboard. Armoring expands text by about 35%.

Decryption can fail if the ciphertext is corrupt or the key is wrong. A failed decryption is detected if the ciphertext footer is missing, the unescaped ciphertext is not a reasonable length, or when it leads to nulls in the plain-text. Some failed decryptions may not be detected (but they are usually pretty obvious).

VII. Weaknesses

The hash algorithm for converting the pass phrase to a key is not very good. Pass phrases of 16 characters or less are taken directly as a key. Longer pass phrases are converted to 16-byte keys in a rather ham-fisted way. Most encryption program instructions would at this point lecture you on the importance of choosing a very long pass phrase that contains a lot of randomness and is difficult to guess. I know that you have to Graffiti the pass phrase in every time you run the program, and will probably pick something short. That's ok, but you will suffer a corresponding loss of security.

VIII. Backwards Compatibility

CCrypt version 2.x.x will decrypt data encrypted using CCrypt version 1, which used a different algorithm (Wheeler and Needham's Tiny Encryption Algorithm). It assumes that any ciphertext that doesn't contain a header block was encrypted with version 1. Data encrypted using version 2 cannot be decrypted by version 1.

In the unlikely event that your version 1 encrypted text starts with "arQx", CCrypt versions 2.1 and up will assume it's ASCII armored and garble it. The chances of this happening are very low.

CCrypt version 2.1.0 was incapable of decrypting strings encrypted at times for which TimGetSeconds() returned a time field containing a null character. CCrypt version 2.1.1 fixes this problem (and will in fact decrypt such strings even if encrypted with version 2.1.0).

IX. Bugs

The IDEA and TEA code in algs.c is not very machine-independent. It's also exceptionally ugly, being patched together out of scraps of code that fell off the back of a truck somewhere.

X. Version History

XI. Copying

GNU GENERAL PUBLIC LICENSE <www.gnu.org/copyleft/gpl.html>

Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA   Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

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The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

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1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

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NO WARRANTY

11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

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XII. Disclaimers

This program is provided "as is". The authors accept no responsibility for damage resulting from the use of this program and disclaims all warrantees (including implied warranties of merchantability or fitness) to the fullest extent allowed by law. On the whole, the authors would be a lot happier if this program were not used to do anything seriously illegal.