[dm-crypt] some explanations would be welcome

Lars Winterfeld lars.winterfeld at tu-ilmenau.de
Tue Aug 2 13:32:49 CEST 2016


Hi.
Try using the if= and of= arguments for dd. Does that make a difference?
Cheers.

Am 28.07.2016 um 18:32 schrieb Pascal:
> hi,
> 
> I've a large file (some Gb) that I want to encrypt without copying it,
> so I do this :
> 
> # md5sum myfile
> d2e539a1ff722e9f8f8f97605ca4ec1e -
> # cryptsetup --type plain open myfile enc
> Enter passphrase:
> # dd bs=4M < myfile > /dev/mapper/enc
> w+1 records in
> w+1 records out
> x bytes copied, y s, z MB/s
> # md5sum < /dev/mapper/enc
> d2e539a1ff722e9f8f8f97605ca4ec1e -
> 
> and all is ok for encryption.
> now, I want to decrypt my encrypted file in the same way, so I do this :
> 
> # dd bs=4M < /dev/mapper/enc | md5sum
> d2e539a1ff722e9f8f8f97605ca4ec1e -
> 
> it starts well but the result does not go as desired :
> 
> # dd bs=4M < /dev/mapper/enc > myfile
> w+1 records in
> w+1 records out
> x bytes copied, y s, z MB/s
> # md5sum myfile
> 120f0695aa0c2c0940f8a5a4c0bbd18f -
> 
> I tried increasing the bs (32M) but the result is the same :-(
> 
> what is my problem ?
> 
> regards.


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