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Header with metadata

Posted: 10/20/2015 09:35:31
by vandernyt (Basic support level)
Joined: 09/16/2015
Posts: 10

I'm considering and editing the MapperAES sample.
First of all, I want to write header with metadata to the beginning of the file.

My metadata has 4096 bytes and contains below information:
- identificator, which shows that file is encrypted or not.
- info about a future algorithm(name, mode, padding, block size and etc).
- etc

[new file's content] = [metadata] + [original file's content]
[new file's size] = [4096 bytes] + [original file's size]

Note that encrypting is not applied to the files's content now. It would be the next step.

Writing is done successfully. But reading is always failed.
In case if file is read from virtual disk - metadata is skipped. All files are readable.
In other cases user can not read a file, since metadata will corrupt it.

Is it possible to do that?
I tried to create my own offset in the EncryptContext::Read and changed EndOfFile, but there was no result.
How can I skip correctly my metadata, can you give me an advice?
Posted: 10/21/2015 00:30:12
by Volodymyr Zinin (Team)

Thank you for the interesting of our product. As I understand you want that an unencrypted yet file can be readable even without use of CBFS (not via CBFS virtual diak). I.e., for example, a user can find it on a physical disk, double click on it, an the file will be opened. If so then as a variant don't place the metadata to the "body" of the file, but move them to an additional data stream (ADS). For example let a file has name "1.txt" and the metadata is in "1.txt:my_cbfs_metadata". Or don't attach the metadata with files at all, but place them separately. For example in a special directory.
Another way is to use additionally another our product CallbackFilter. By means of it you can modify file data on the fly at the time it is being read or written. So in this case the metadata can be placed in the "body" of the file.



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