CryptoBola, About

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Bemerkungen:

Eine Erklärung der Begriffe, Abkürzungen und Akronyme befinden sich auf der Seite Digitale Geheimnisse.
The dialog (the entire process of imbedding and extracting) can be done in much fewer steps than the tutorial shows. The goal of this description is to present all the options, not to optimize the time spent working with CryptoBola JPEG.
Red frames in the dialog window captures mark spots of particular interest in the specific context.
File specifications have to be complete with drive and path name, except if the file is in the working folder of the CryptoBola JPEG application (the working folder is specified in the shortcut of the application).
Following Help functions are offered:
- clicking on the HELP button presents the complete description of all details,
- right-clicking on any enabled button or on most input fields, a small help text pops up, explaining the function of that button or the meaning of the input data,
- pressing F1 displays a small pop-up help related to the button or input field, which actually has the focus (the focus can be placed on an enabled button or input field by pressing tab). This works even on input fields, which don't show any help text when right-clicked (file names, passphrases).

How to imbed data into an image

Select the imbedding function on the initial window

Specify and validate the JPEG file to be used as the basis (to be modified by the source data) in the JPEG basis file area of the window by entering the file name, or selecting it in a browse dialog

The Validate button became enabled. The validation consists of the formal verification and evaluation of the image's imbedding capacity.

The text appearing after validation shows the maximum amount of data can be imbedded in the JPEG image at what "cost in picture quality", i.e. maximum distortion of the picture when imbedding that amount of data. This calculation assumes, that every bit involved in the imbedding process will actually be changed, while in fact statistically only about half of the involved bits undergo a change. The actually imbedded amount of data should not come close to this limit, since it would make the distortion effect easily noticable.

maximum 36696 bytes can be imbedded in this JPEG image; the maximal picture distortion would be 43.72% when imbedding that amount of data

The data to imbed has to be specified; use the Source of data to imbed group of controls

The data to be imbedded can be entered and/or pasted in the edit dialog, if the Edit button will be clicked on (see the edit/view dialog).

Alternatively, by clicking on the File button, the Browse button and the box for the file name will be enabled and a file can be selected as the source of data.

The source file can be specified directly by entering its name, or a browse dialog can be started for the file selection

When Validateing the source against the basis, the file will be read and it's length compared to the capacity of the JPEG basis

The response contains the distortion, which can be caused by imbedding this data in the image data. In this example the maximum distortion is 13.19%, caused by imbedding 25009 bytes

At this point the data may be edited and validated again. The original source file will not be effected by the changes made while editing. The finalized (or unchanged) data can now be imbedded in the basis by clicking on the Imbed button; this will start a subdialog for entering the passphrase:

The same passphrase has to be entered in two fields to verify that no typo has been made.

Initially an asterisk appears for each character. The copy/paste functions do not work on these fields in this state

By selecting Show typing, the entered characters become visible; the passphrases can be verified visually.

In this state the copy/paste functions can be used. However, it is a very bad practice to enter a passphrase in one of the fields and copy/paste it in the other field, for it defeats the purpose of the repetition (any typo made in the first field will be repeated in the second one)

By clicking on OK the passphrase (no matter if actually shown or not) will be verified and if it is correct, the actual imbedding takes place:

The amount of imbedded data and the actual distortion it caused in the image is shown (here 6.59%). This is usually close to the half of the maximum distortion indicated before imbedding (in this example it was 13.19%).

The modified image can be saved into a file; use the JPEG target file group of controls.

The target file can be specified directly by entering its name, or a browse dialog can be started for the file selection.
By clicking on the Save button the file will be saved

Note, that the resulting file is smaller (153933 bytes) than the original was (158641 bytes). This is not always so, and it has nothing to do with the quality of the image

Now the resulting image can be verified by a JPEG viewer in order to determine if the distortion is acceptable. By clicking on the RESTART button the dialog can be restarted. Note that the imbedded data remains in storage, it can be further edited and imbedded in another image.

How to extract imbedded data

Select the extracting function on the initial window

Specify and validate the JPEG file, which contains the imbedded data in the JPEG basis file area of the window by entering the file name, or selecting it in a browse dialog

As soon as a file name has been selected or entered, the Extract button becomes enabled

By clicking on the Extract button, the extraction process begins by asking for the passphrase:

Enter the password exactly as it has been given when imbedding

Initially an asterisk appears for each character. The copy/paste functions do not work on this field in this state

By selecting Show typing, the entered characters become visible; the passphrases can be verified visually.

By clicking on OK the passphrase will be verified and if it is formally correct, the extraction takes place:

The response shows the amount of extracted data, here 25009 bytes

If a wrong passphrase was entered, RESTART the processing or change any character in the JPEG basis file name and change it back; the Extract button becomes enabled again. This can happen already directly after Extract, when the length of extraction indicates, that the passphrase can't be correct (or when displaying the extracted data shows something unexpected).

If the following passphrase will be entered (note that "the" is missing between "for" and "online"),

then already the length of extracted data shows, that the extraction was not really successful

However, the person extracting the data does not always know the length of the imbedded data. Let's take a look at the extracted data in the Edit window by clicking on the Display button:

This does not look like text, what we have expected. The correct passphrase can be specified by restarting the extraction process

The extracted data can be viewed and changed in the Edit dialog, see the edit/view dialog, and/or it can be saved in a file with or without having viewed or changed it before.

Clicking on File enables the Browse button and the file name field

The file can be specified directly by entering its name, or a browse dialog can be started for the file selection

By clicking on the Save button, the file will be saved

The extraction process is now finished. By clicking on the RESTART button, the dialog will be restarted. Note that the extracted data can still be viewed; it can be edited and used as source data in the next imbedding process.

The edit/view dialog

The edit/view dialog can be started at any point during the imbedding or extraction dialog. This dialog facilitates

entering text data before imbedding,
viewing and changing the data from the source file before the imbedding will be carried out,
viewing the extracted data before or instead of saving it in a file,
changing the extracted data before saving it, or before imbedding it again.

Entering/changing data occurs in a temporary storage. When leaving the edit dialog with clicking on OK, the data from this storage will be kept; by clicking on CANCEL or pressing Escape the temporary data will be discarded.

The so-called Rich Text Editor will be used for entering/viewing/changing the data. It has some formatting capabilities, comparable to word processors but in limited extent. Microsoft's Word for Windows as well as WordPad support the rich text format; the default file name extention for such file is "rtf".

This edit dialog does not aim at substituting full-fledged word processing. If sophisticated text formatting is required, it should be done before imbedding respectively after extraction. However, the edit dialog provides a simple way to enter and view data.

The editing window is resizable: it can be stretched or shrunk in any direction by dragging a side or a corner of the window; it can be minimized, maximized and restored to the previous size.

Changing between rich edit format and text format

When starting out with the edit/view dialog, the check box Rich Edit Format is not checked. The meaning of this is, that any data, which has been extracted or read from a source file will be displayed without looking for rich text formatting information. This setting is suitable for viewing plain text or anything else, what is not in rich text format.

It is appearant, that a JPEG image in JFIF format has been imbedded (or is about being imbedded) into the basis image

When displaying this content in rich text mode, which is not conform with rich text format, an empty edit box would appear.

Now let's take a look at the appearance of some rich text:

The character string {\rtf1\ansi at the very beginning indicates, that the content is in rich text format

Checking the box Rich Edit Format lets the editor interpret the formatting information

Switching back to non-rich edit format eliminates the formatting information; now only the plain text will be displayed

Care has to be exercised not to inadvertantly save the data, which has been changed by switching back and forth between rich text and plain text format. (The program will ask for confirmation before storing the changed data.)

When pasting rich text from somewhere in the edit box, it will be displayed in formatted mode independently on the current setting. However, when changing the mode from rich text to plain text, the formatting information will be eliminated.

Due to limitations of this rich edit format support, when loading a file or extracted data or pasting a rich text in the exit box, some changes may be carried out. When saving the data, these unintended changes will become permanent. This can be avoided by clicking on CANCEL instead of OK.

Font selection

A rich text usually contains font specifications as well. Even several different fonts (different type-faces, styles and sizes, etc.) may be used in the text; there is no point in changing font. However, in plain-text mode one can choose between a proportional font (actually "MS Sans Serif") and a fixed-pitch font (actually "Courier New"). In plain-text mode the font size can be chosen as well. Note, that the font type and size chosen this way does not become part of the data; it changes only the view, as opposed to the font characteristics of rich text.

Anfang Geändert: 2004-09-01