Encrypting/Decrypting file holding binary data

[wayne08]

How to encrypt/decrypt a file that has binary data in it..

its a sort of database file. a number of records of fixed length stored in it. i've used fwrite to write each record (structure).

i tried reading byte by byte and adding a key value to the byte but obviously it doesnt work.

I know the the file is not human readable anyway but still..i want to put it as an "extra security feature"

Any other way?

[MK27]

Read this:
SourceForge.net: Serialization - cpwiki

It's about exactly what you are doing (serializing data). You probably don't need to change the data at all (post the struct definition here to make sure).

I wrote that article, so you can ask questions about it. The "tofile" and "fromfile" functions work pretty well as is.

[Subsonics]

It's trivial to get to the parts of the file that is readable ie plain text, either by hexdump or by reading in the file and printing only after a check like this:

if( isprint(line[i]) ){
        //print here
}

[wayne08]

my file is not readable as such anyway..

i am writing simple structures having 3 float values to the file.

and i can print the values back also

what i want is that if i enter the WRONG KEY, then it should display the contents, however, garbage contents..

hope u get what i mean..

[MK27]

my file is not readable as such anyway..

Yes. I understand EXACTLY what you are talking about and that wiki article is about EXACTLY that. Your file IS readable that way (but not the way Subsonics is on about).

i tried reading byte by byte and adding a key value to the byte but obviously it doesnt work.

You have not really explained yourself here, if this is the real issue, why don't you post the code you used so someone can understand what you are referring to? Again, I suspect you do not need to do this at all. READ THE ARTICLE. It will take 5 minutes.

[laserlight]

what i want is that if i enter the WRONG KEY, then it should display the contents, however, garbage contents..

A simple way is to use the help provided by the wiki article that MK27 linked to, except that after you are done, you encrypt the file contents. For the encryption itself, a library like mcrypt could come in handy.

[MK27]

Ahhh...that's what "key" is about, sorry . I would just use one for the entire file, as laserlight implies. Post your code wayne.

[Subsonics]

I know the the file is not human readable anyway but still..i want to put it as an "extra security feature"

Understand, that I am only responding to this line. I don't know what's in your file, since you failed to mention it. It's should be obvious, but simply writing the file in binary form, isn't giving you any kind of security from prying eyes, that's all.

(but not the way Subsonics is on about).

Yes it is.

[wayne08]

@MK27 - yes i read the article.. that is what i have done. thanks. however, it doesnt say on encrypting the file.

@laserlight - i read about mcrypt but i'm not sure what i am to do to use it. Is it a library file already present in turbo c or what? i'll look into it anyway..

@subsonics - i guess i didnt put it that well . sorry for that. nevermind.


thanks for response guys. i managed to work some other, rather trivial, ways out.

[laserlight]

i read about mcrypt but i'm not sure what i am to do to use it. Is it a library file already present in turbo c or what?

You probably need to download libmcrypt from one of the links listed, learn its API, and then use use it.