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Encrypting Editor Notepad replacement

, 18 Apr 2013
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Source code for an encrypting editor Notepad replacement.
This is an old version of the currently published tip/trick.

Introduction

I love Windows Notepad! It is my favorite editing tool. It is fast and simple. So, why would I write a replacement program?

The primary purpose of the CryptPad program is to provide optional file encryption. This is valuable for files which contain sensitive information. Unlike many other encryption solutions, this one only encrypts and decrypts one file at save and open. There is never a decrypted version of the file stored unless the operator (I am a little uncomfortable with the word "user") specifies to remove the encryption. The file can be stored multiple places and moved freely, but always in encrypted form. Anyone who knows the encryption string can read the file with this program.

Because of the importance of maintaining multiple passwords for better security, I have a file with all the passwords in it that I use. This is also a security risk unless the file is encrypted. I have examined many encryption solutions and none does exactly what I need. I need to be able to transport and store an encrypted file anywhere I want. Encrypted drives are not what I need. The file must never exist in decrypted form. Therefore I need a simple editor which opens, decrypts, edits, encrypts, and saves a file.

Notice that I do not at any point describe CryptPad as a Notepad clone. A clone is an exact copy. Notepad has some very specific functionality, which I have seen nobody duplicate completely. For example, the Undo function of Notepad has not been fully implemented in most "clones". I have also not seen a "clone" which properly implements UTF-8 and Unicode conversions or reads files with ANSI characters as Notepad and CryptPad do.

CryptPad is intended to be nearly the same as Windows 7 Notepad. I have chosen not to include some functions which I do not consider useful or important such as printing. I almost never use paper or printing! CryptPad is not a "clone" but is close enough to be a useful replacement. Now that I have the source code for a replacement for Notepad, I have been adding functions useful in my daily editing.

I hope you find the CryptPad program useful. I am interested in any problems you may find in the program and in particular any incompatibility as a Notepad replacement. I am also interested in your ideas about improving this simple program. I intend to keep the program as small and simple as practical.

You may refer to the original website for additional details about the CryptPad program:

http://www.frank-t-clark.com/Professional/Papers/CryptPad/CryptPad.html[^]

UTF-8

As you read about the program, you might like to ask me a question. What in the world is all this UTF-8 and Unicode nonsense!? In the old days of microcomputers (about 1980) it was simple. (It wasn't really, but we will pretend it was.) All text files were 7 bit ASCII, characters. There are many people in the world, with many different languages and characters, and they need to be represented in daily computer use.

If you are up for a heavy read, you can start here:

http://en.wikipedia.org/wiki/UTF-8

I will try to make it short and simple. When you are using typical ASCII characters, strict UTF-8 (without BOM) is exactly the same thing. Most of your editing will be simple ASCII. In most cases, you can just stop here.

The exception is if you ever use characters such as Microsoft Word smart quotes. These are the "curly" typographical equivalents of the simple ASCII quote. They have a different curve for beginning and ending a quote. There are many other types of special characters.

There are two ways to represent these types of non-ASCII characters. The older way is with 8 bit characters. This is when you see "Windows-1252" or other non-Unicode encodings. These encodings can be very complex. Notepad refers to this as "ANSI" encodings. Unicode makes the process simpler (but not simple) to support everybody's characters. UTF-8 was invented to support ASCII with no changes and optionally extend to Unicode characters.

If this short explanation made you curious to know more, then you are back to the heavy reading I mentioned earlier.

Installing the Program

Program installation is recommended for a CryptPad directory under the Documents directory for an individual user. The Program files directory can be used for an administrator install for all users. "Open With" can be set to default to CryptPad for the .SAFE encrypted files created by CryptPad. The program is completely stand-alone so a simple copy is all that is needed to install. You can carry it on a USB stick and use anywhere.

I do not provide an install program because I want you to know for absolute certain exactly what is required to use the program. Uninstall is very simple. Erase the program! Setup programs mysteriously make unknown changes to your computer. I won't even change the registry for you. I provide the complete source so you can know for certain exactly what the program does. Compile it for yourself, if you are able. Examining the code is not easy but it is available, if it is a concern to you. By these methods, you can trust the software. There is so much out there that is not trustworthy. You don't have to trust me. Full disclosure is the best trust there is.

You might choose to set the default "Open With" to CryptPad for .TXT also to take advantage of the additional editing functions. A REG file is provided which contains all kinds of settings I use to make CryptPad the default editor. These have been used and tested on Windows 7. I now use CryptPad to edit everything where I would have used Notepad. I used the "Default Programs Editor" freeware download, which works great. It is highly recommended.

The program is compiled with the .NET framework version 3.5, which is included automatically with the Windows 7 OS. The program has only been well used and thoroughly tested with the Windows 7 OS.

The program has only been used a little with the Windows 8 OS (Yuck!).

The program has not been used or tested with Windows Vista or XP. Unfortunately, the .NET framework version 3.5 is not installed in Windows Vista or XP so you will need to install it to use the program in Windows XP. There are likely to be issues with the program. I don't use XP anymore so I won't be able to help you.

Using the Code

I have provided the complete VS2010 C# project zip file with the executable and the complete source code for CryptPad, the encrypting editor Notepad replacement program for those who enjoy software code. You might be interested in adding your own special functionality.

I hope you find the source code instructive for picking up some ideas. I have learned a lot by examining the code of others. I hope examining my code will be useful to you.

Points of interest

The novel aspects of the program source code are the encryption. The program uses a quick and simple scrambling algorithm of addition/subtraction based on a secret encryption string provided by the operator. The program encrypts only ASCII so that I have a contiguous arithmetic range. The intent is to continue to use text rather than binary processing.

These example excerpts are not identical to the supplied source.

private string Encrypt (string str)
{
    StringBuilder st = new StringBuilder (str);
    for (int i = 0; i < st.Length; ++i)
    {
        int chr = st[i];
        if (isASCII ((char) chr))
        {
            chr = ' ' + ((E (i) + (chr - ' ')) % 95);
            st[i] = (char) chr;
        }
    }
    return st.ToString ();
}

private string Decrypt (string str)
{
    StringBuilder st = new StringBuilder (str);
    for (int i = 0; i < st.Length; ++i)
    {
        int chr = st[i];
        if (isASCII ((char) chr))
        {
            chr = ' ' + ((chr - 32) - E (i) + 95) % 95;
            st[i] = (char) chr;
        }
    }
    return st.ToString ();
}

The encryption string is scrambled with a pseudo-random number seeded with a checksum of the encryption string

private int E (int i)
{
return (encryption_string[i % encryption_string.Length]
 + i + i * random_seed) % 95;
}

// plus checksum for random_seed
private int Checksum2 (string str)
{
    int checksum = 0;
    for (int i = 0; i < str.Length; ++i)
    {
        checksum += str[i];
    }
    return checksum;
}

The program uses an additional XOR checksum placed in the file to catch typos in the encryption string. This is critical to verify input since the encryption string is password masked. I protect short encryption strings by extending it to at least 32 characters.

// xor checksum for in the file
private uint ChecksumXOR (string str)
{
    uint checksum = 0;
    int j = 32;
    if (32 < str.Length)
        j = str.Length;
    for (int i = 0; i < j; ++i)
    {
        uint t = 0;
        if (0 < (0x80000000 & checksum))
            t = 1;
        checksum <<= 1;
        checksum |= t;
        checksum ^= str[i % str.Length];
    }
    return checksum;
}

I would not claim the encryption used by this program is CIA quality but I think you will find it is highly effective. The strength of the encryption is highly dependent on the length of the encryption string. A strong string of ten characters or more is not likely to be broken by anyone except a skilled cryptologist. I am not a skilled cryptologist but I am familiar with some aspects of cryptology. The primary attacks against this encryption have been anticipated.

I have thought about offering a challenge to see if a clever hacker or skilled cryptologist would take an interest and break it. I would be interested to know how long it took, what type of equipment was needed, and what attack vector succeeded.

The most likely attack would be against the XOR checksum used to verify the encryption string against typographical error. This type of attack depends on the strength of the encryption string you choose.

History

  • Version 1.9 released 2013-04-18:
    • Major code review and revise.
    • Improved graphics and icon modified from Notepad.
    • Fixed find direction up.
    • Fixed some missing Verdana 12pt settings.
    • Discard previous file completely at Open of a new file.
    • Replace All was too slow and would not undo all so changed to match Notepad.
    • Improved all Undo function to match Notepad.
  • Version 1.8.0.0 released 2013-04-10:
    • Improved layout of popup windows to center and to avoid going off the edge of the screen.
    • Fixed find and replace non-modal dialogs to not conflict or duplicate and other action changes.
    • I also made the find and replace dialogs smaller again but sizable.
  • Version 1.7.0.0 released 2013-04-05:
    • Window Position does not remember maximized or minimized.
    • Moved some new functions to a new Tools menu.
    • Added a search to find non-ASCII characters.
    • Added a search for the longest line.
    • Do not allow changes to a file opened read-only.
  • Version 1.6.0.0 released 2013-03-31:
    • Added User Setting persistence for the current directory.
    • Added version upgrade for User Settings.
    • Adjusted the handling of file encoding on save to use Unicode BOM where specified or appropriate.
    • Added an option to force ANSI encoding before the file is written.
    • The Status Bar shows the current file encoding.
    • The visibility of display items on the Status Bar can be individually selected.
    • The program will still warn and require confirmation for a file over about 2MB but will allow any file size no matter how slow it becomes.
    • Set the textbox MaxLength to 0, use all available memory, which allows the program to crawl and/or crash, if the operator specifies a file which is just too big.
    • Fixed the problem with a creeping Window Position.
  • Version 1.5.0.1 released 2013-03-27:
    • Corrected an exception which occurred when a blank encryption string is entered.
    • Improved the wording of the prompt requesting the encryption string.
    • Expanded the information displayed on the status line.
  • Version 1.5.0.0 released 2013-03-25:
    • Added C-type escape character processing to the find and replace functions for some common characters.
      • \n New line
      • \r Carriage return
      • \t Horizontal tab
      • \\ Backslash
      I also made the find and replace input textboxes wider. The Paste, Copy, and Cut functions support the new escape characters.
    • I modified the XOR algorithm to recognize encryption strings longer than 32 characters and be more accurate as a checksum to identify typos in the encryption string.

      If you have used CryptPad to make important encrypted files in an earlier version, you will need to convert the encrypted file because the file header is incompatible with version 1.4 and earlier encryption.

      The typical conversion process requires you to copy and paste the plaintext of existing encrypted files from the version 1.4 or earlier program to the version 1.5 or later program and save with the new encryption.

  • Version 1.4.0.0 released 2013-03-22:
    • Added View, Status Bar.
    • Added User Setting persistence for Word Wrap, Font, Window Position, and Status Bar.
  • Version 1.3.0.0 released 2013-03-17:
    • Handle ANSI, UNICODE, and UTF-8 files. Provides conversions.
  • Version 1.2.0.0 released 2013-03-15:
    • Changed the program icon from a generic icon to a custom design.
    • Added the "Edit" option "Transpose" to switch the character to the left and right of the cursor. I don't know how often you have a problem with transposing characters as you type but it happens to me a lot.
    • Added registry file to automatically use CryptPad for selected file types.
  • Version 1.1.0.0 released 2013-03-08:
    • Added the QuickCrypt function.
    • Required the encryption string to be at least four characters. Strengthened the checksum and encryption header. Corrected loss of the '~' character. Scrambled the encryption string. Incompatible with version 1.0 encryption. You must copy and paste the plaintext of existing encrypted files from the version 1.0 program to the version 1.1 program and save with new encryption.
    • Corrected some confusion with the initial directory on a "Save As" after a command line open.
    • Finished the Replace function, corrected dialog inconsistencies, and improved Notepad similarity.
    • Changed Edit menu option "Capital&ize" to "&Initial Capital"
    • Increased textbox.MaxLength from 32KB to 15MB. Generate an error and fail the open if the file size is greater than 10MB. Generate a warning if the size is greater than 5MB.
  • Version 1.0.0.0 released 2013-03-01:
    • These are the new and changed features compared to Notepad.
    • Only ASCII is supported in the encryption functions. Non-ASCII characters will not be encrypted. The initial encryption algorithm is not particularly sophisticated but it is completely effective to block the curious and prying. This is not intended to be a high security solution!
    • Automatic random password generation for websites. The sophisticated password would be stored in the encrypted file so you don't have to remember it. A typical line or sequence of lines in the file would have the website address, the email address/username, and the password for a quick and simple copy and paste to login.
    • The file is held open to reduce accidental multiple change problems. Read share only. Therefore, a read-only option is allowed on open.
    • The secondary purpose is to provide some enhanced functionality for general file editing:
    • Uppercase, lowercase, capitalize selection conversion.
    • Word wrap toggle remembers cursor location. Unlike Notepad it does not jump you to the beginning of the document.
    • Replace All leaves the last changed selection highlighted instead of jump to the beginning.
    • Go To works with word wrap on though the meaning is changed to wrapped line numbers.
    • The default directory for "Open" and "Save as" is initially the documents directory and becomes the directory of the last opened or saved file in the current session.
    • The Verdana font at 12 point is used in all program controls. This provides higher visibility for easier readability.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Frank T. Clark
Systems Engineer Three Angels Broadcasting Network
United States United States
I am a Software Systems Design Engineer experienced with IEEE standards and the entire IEEE software development life cycle. Concept Exploration, Requirements, Design, Implementation, Test, Installation and Checkout, Operation and Maintenance. I enjoy working with people and solving customer problems.
 
I am currently employed as Information Technology Staff in the religious satellite broadcasting industry.

Comments and Discussions


Discussions posted for the Published version of this article. Posting a message here will take you to the publicly available article in order to continue your conversation in public.
 
QuestionGPG Pinmembercspitzer29-Jul-14 10:37 
AnswerRe: GPG PinprofessionalFrank T. Clark29-Jul-14 10:49 
GeneralRe: GPG Pinmembercspitzer29-Jul-14 10:52 
GeneralRe: GPG PinprofessionalFrank T. Clark29-Jul-14 10:54 
QuestionMultiple mapping Pinmemberfeanorgem29-Jul-14 6:43 
AnswerRe: Multiple mapping PinprofessionalFrank T. Clark29-Jul-14 10:43 
GeneralRe: Multiple mapping Pinmemberfeanorgem29-Jul-14 12:55 
GeneralRe: Multiple mapping PinprofessionalFrank T. Clark1-Aug-14 11:07 
GeneralRe: Multiple mapping Pinmemberfeanorgem1-Aug-14 15:49 
QuestionClarifying what you mean... PinmemberMember 873926921-Jul-14 9:17 
AnswerRe: Clarifying what you mean... PinprofessionalFrank T. Clark21-Jul-14 11:33 
GeneralRe: Clarifying what you mean... PinmemberMember 873926927-Jul-14 1:57 
SuggestionRe: Clarifying what you mean... PinprofessionalFrank T. Clark27-Jul-14 2:28 
GeneralRe: Clarifying what you mean... PinprofessionalFrank T. Clark28-Jul-14 4:36 
GeneralRe: Clarifying what you mean... PinmemberMember 87392693-Aug-14 2:02 
GeneralRe: Clarifying what you mean... PinprofessionalFrank T. Clark3-Aug-14 10:54 
GeneralRe: Clarifying what you mean... PinmemberMember 87392694-Aug-14 9:42 
QuestionApparently a file path cannot be relative? PinmemberMember 873926920-Jul-14 2:40 
AnswerRe: Apparently a file path cannot be relative? PinprofessionalFrank T. Clark20-Jul-14 4:26 
AnswerRe: Apparently a file path cannot be relative? PinprofessionalFrank T. Clark20-Jul-14 5:24 
AnswerRe: Apparently a file path cannot be relative? PinprofessionalFrank T. Clark21-Jul-14 8:54 
BugAbout window Pinmembermavru3-Jun-14 0:18 
GeneralRe: About window PinprofessionalFrank T. Clark3-Jun-14 3:09 
QuestionGreat article and very interesting! PinprofessionalVolynsky Alex6-Apr-14 12:51 
AnswerRe: Great article and very interesting! PinprofessionalFrank T. Clark7-Apr-14 2:39 
GeneralRe: Great article and very interesting! PinprofessionalVolynsky Alex7-Apr-14 8:05 
GeneralMy vote of 3 Pinmemberwebmaster4426-Apr-14 9:48 
GeneralRe: My vote of 3 PinprofessionalFrank T. Clark6-Apr-14 9:52 
GeneralRe: My vote of 3 PinmemberDave Cross7-Apr-14 2:15 
QuestionNo other editor with ANSI, UTF8 and Unicode support PinmemberAndreas Falco11-Feb-14 7:32 
AnswerRe: No other editor with ANSI, UTF8 and Unicode support PinprofessionalFrank T. Clark11-Feb-14 7:56 
GeneralRe: No other editor with ANSI, UTF8 and Unicode support PinmemberAndreas Falco11-Feb-14 8:48 
GeneralRe: No other editor with ANSI, UTF8 and Unicode support PinprofessionalFrank T. Clark11-Feb-14 9:45 
AnswerRe: No other editor with ANSI, UTF8 and Unicode support Pinmemberahagel7-Apr-14 8:46 
AnswerRe: No other editor with ANSI, UTF8 and Unicode support PinmemberOscar030-Jul-14 9:17 
QuestionAbsence of printing capability.. Pinmembermungball9911-Dec-13 5:26 
AnswerRe: Absence of printing capability.. [modified] PinprofessionalFrank T. Clark11-Dec-13 11:10 
GeneralRe: Absence of printing capability.. Pinmembermungball9916-Dec-13 8:55 
GeneralRe: Absence of printing capability.. PinprofessionalFrank T. Clark16-Dec-13 10:38 
QuestionI vote you 5 PinmemberWuRunZhe9-Dec-13 14:21 
AnswerRe: I vote you 5 PinprofessionalFrank T. Clark10-Dec-13 1:55 
GeneralMy vote of 5 PinprofessionalPrasad Khandekar23-Sep-13 21:36 
GeneralRe: My vote of 5 PinprofessionalFrank T. Clark24-Sep-13 2:10 
GeneralRe: My vote of 5 Pinmembermatrixcd20-Nov-13 20:41 
GeneralRe: My vote of 5 PinprofessionalFrank T. Clark21-Nov-13 3:27 
BugException when trying to save a file as safe without a key [modified] Pinmember_Nizar23-Sep-13 21:05 
GeneralRe: Exception when trying to save a file as safe without a key [modified] PinprofessionalFrank T. Clark24-Sep-13 2:09 
QuestionEncryption/Decryption Algorithm PinprofessionalMuhammad_Shoaib23-Sep-13 18:56 
AnswerRe: Encryption/Decryption Algorithm PinprofessionalFrank T. Clark24-Sep-13 2:08 
GeneralRe: Encryption/Decryption Algorithm PinmemberRick Bassham7-Oct-13 11:26 

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