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The answer is: not necessarily. For example, in mathematics there is a class of proofs called "existence proofs" that show an answer exists, but don't give the answer.
Prime factorization comes to mind. We can answer "yes" to the question of whether a large number can be expressed as a product of primes. Computing those primes, however, can be extremely difficult.
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Alan Balkany wrote: Computing those primes, however, can be extremely difficult.
Thankfully, this is very difficult. Our current encryption algorithms depend on it. 
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See also the subset-sum problem...
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Hi guys...I am from Bangladesh and my knowledge is very limited.I have developed an algorithm using which any data can be hidden in a text file.After hiding the data in the text file,the size of the text file remains absolutely unchanged and there is no change whatsoever in the file's content as far as reading the file is concerned.I know there r lots of data hiding techniques.Guys can you plse tell me if this techniq has already been implemented the way i have done it...I mean hiding the data in a text file without changing the file size even by a single byte and you wont see a single replacement/change/distortion in any of the letters of the file.As far as reading the file is concerned...the file will remain 100% unchanged even after hiding the data in it.
modified on Tuesday, March 18, 2008 8:42 PM
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Let me get this right. Your algorithm hides data in a file but doesn't alter the file in any way?
Does it look anything like this?
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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Hiding information in text, isn't that what documentation is about?
Luc Pattyn [Forum Guidelines] [My Articles]
This month's tips:
- before you ask a question here, search CodeProject, then Google;
- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
- use PRE tags to preserve formatting when showing multi-line code snippets.
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It hides the data in a file and it does not change the file size and no visible change whatsoever in the file.
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Your original post states 'the file will remain 100% unchanged'. If you're not changing the file, how can you be hiding data in it? What you're saying just doesn't make sense.
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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I said 100% unchanged as far ar reading the file is concerned.
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Pallab_GT wrote: I said 100% unchanged as far ar reading the file is concerned.
How can you make this claim? In order to hide the data, you are going to have to modify some characters in the file. If I use a diff tool to compare the old and new versions of the file, it's going to flag up some differences. If you make changes to a file, they're going to be noticed.
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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pmarfleet wrote: How can you make this claim? In order to hide the data, you are going to have to modify some characters in the file. If I use a diff tool to compare the old and new versions of the file, it's going to flag up some differences. If you make changes to a file, they're going to be noticed.
You're wrong.
You wrote all the above because you're not aware of occultism superanatural powers.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
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You read it wrong.I said AS FAR AS READING THE FILE IS CONCERNED,the file remains 100% unmodified.Ofcourse i have to make some modification but that does not affect the size of the file or for that matter the readability of the file even by a bit.
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Do you know a text file contains just character codes?
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
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I know that a text file contains only character codes.And knowing that i am claiming that i can hide data in the text file without replacing/changing/distorting any of the readable letters.
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Pallab_GT wrote: i am claiming that i can hide data in the text file without replacing/changing/distorting any of the readable letters
Then your claim is obviously false. Common sense dictates that data cannot be hidden in a file without requiring the file to be modified. If the file is modified, a diff tool will pick up the changes. If you still believe your claim is true, you are more deluded than I first thought. If you want to perform miracles, maybe you should consider changing careers and become a magician instead of a software developer.
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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You are missing one point again and again...i am insisting upon the fact that i am not going to change/replace/distort any of the READBLE CHARACTERS.
Before u pass comment u should know that it is not necessary that you will know each and every trick of software development.There might be things beyond ur knowing.One more thing...No body in this world knows everything.
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Pallab_GT wrote: i am not going to change/replace/distort any of the READBLE CHARACTERS
All characters in a text file are readable. That's the whole point; data is stored in text files so it can be read by humans as well as computers. Have a look at the ASCII table[^]. Notice anything? That's right, all the characters are human-readable. Now ask yourself this: if all ASCII characters are readable, what changes can your algorithm make that won't be easily noticed?
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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Sir,my knowledge of software development is very limted.I am a novice in comparison with u.I know u know a lot more than me.
Can you plse tell me will it be something new if i can do what i am claiming to do?
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Pallab_GT wrote: Can you plse tell me will it be something new if i can do what i am claiming to do?
Not only will it be new, it will be a miracle 
Haven't you learned anything from this discussion? You want to hide data in a text file without making noticeable changes. I have demonstrated to you that any change you make to the file is noticeable. Therefore your objective is impossible.
Paul Marfleet
"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush
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Well Sir,if you comapare the text files(prior and post hiding data versions) bit by bit...there will be obviously some chages.But that change will have no impact whatsoever in any of the readable/printable letters of the file.Not even a single readable/printable letter will be changed/replaced or distorted.Plse note my emphasise on readable/printable letters.There will be some changes in the file in binary level.But,i say again that change in binary level will have no impact whatsoever in the readable/printable letters of the text file,the readable/printable letters will remain absolutely the same as they were before hiding the data.And the size of the file will also remain absolutely unchanged.The size will not change even by a single byte.
Will you still consider it a miracle?
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What do yo mean with. The file will change on a binary level.?
And how wouldn't that have an impact on the readable Text portion of the file?
codito ergo sum
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Sir...can i ask you something?
If a character is not readable/invisible in MS-WORD/WORDPAD/NOTEPAD using all the english (cause i have tried it only using english fonts) font,will you consider that character readable/printable?
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Pallab_GT wrote: If a character is not readable/invisible in MS-WORD/WORDPAD/NOTEPAD using all the english (cause i have tried it only using english fonts) font,will you consider that character readable/printable?
what he is saying is that he, or I, or anyone desiring to see unprintable characters can look at them at a moments notice anytime we choose to. All characters, all ASCII codes from 0 to 255 are readable to a person who knows what they are doing. You may change the space to a hex 00 or higher order hex, but if I know what I am doing I will see it. More to the point "diff" works at both the character and binary level, so it will see that a change has been made and highlight every single change.
I miss out on all the fun discussions....  I missed this until now....
_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
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Sir,if u check other data hiding softwares i think you will the difference between my technic and the conventional technics that r in use.
The whole point is obscuring the data in a text file so that even if the file is intercepted during transfering the file over a network,it should not be noticeable easily that some data is hidden inside the file.
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Pallab_GT wrote: Sir,if u check other data hiding softwares i think you will the difference between my technic and the conventional technics that r in use.
The whole point is obscuring the data in a text file so that even if the file is intercepted during transfering the file over a network,it should not be noticeable easily that some data is hidden inside the file.
I am fully aware of the other programs, and as I understand the issue at hand, you are misleading yourself. If you change any white space to a character other than the original white space, you are instantly obvious about the change. You may not see it in notepad, but upon review of the text, it is immediately obvious. If you qualify your algorithm as hiding only from a computer illiterate, I would understand that it would work perfectly, so would many messages. But upon any change to a so-called "non-printable character" can be and is very visible to most of us here.
_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
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