On Wed, 26 Feb 2014 09:39:02 +0100 Ben RUBSON <[email protected]> wrote: | 2014-02-25 1:36 GMT+01:00 Anthony Thyssen <[email protected]>: | | > On Mon, 24 Feb 2014 14:25:40 +0100 Ben RUBSON <[email protected]> | > wrote: | > | | > | To be sure that all IOs of one file will be aligned, does the encryption | > of | > | 4K of data give exactly 4K of encrypted data ? | > | | > encryption happens in 'blocks of data'. If the data encrypted in | > is less a block in size it increases to that block size. | > | | In this situation, we are sure that all IOs will be aligned. | | However, is the following situation possible ? | Can we have the size of an encrypted block of data bigger than the size of | the block of data itself ? | In other words, can we have : | size(encrypt($block_of_data)) > size($block_of_data) | | This could lead into a misalignment somewhere in the file, or EncFS could | have to read 2 disk blocks to serve 1 data block. | | Thank you, | | Best regards, | | Ben
The encryption block size is very small by comparison to that of disk block size. A typical encryption used today is aes-256 That is 256 bit encryption blocks or 32 bytes per encrypted block. Compare that to disk blocks of 4Kbytes. I/O alignment is no problem, and is actually very common. It is only headers that cause problems, and headers are not that big either, which is why you can pack a lot of per block information into a single 4K header block for each file, so as to preserve I/O block alignment. Anthony Thyssen ( System Programmer ) <[email protected]> -------------------------------------------------------------------------- Aha! I'll bounce off that broad, flat surface and be in a lot of pain! -- Tick, "The Tick" -------------------------------------------------------------------------- Anthony's Castle http://www.ict.griffith.edu.au/anthony/ ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk _______________________________________________ Encfs-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/encfs-users
