[dm-crypt] some explanations would be welcome

[dm-crypt] some explanations would be welcome

[Pascal]

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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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Re: [dm-crypt] some explanations would be welcome

[Lars Winterfeld]

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.

Re: [dm-crypt] some explanations would be welcome

[David Christensen]

On 07/28/2016 09:32 AM, Pascal wrote:
> 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 ?

Is that redacted console output?  It would be better if you posted
complete and accurate console output.


What operating system (name, architecture, version, etc.) are you using?


Please provide a URL to the manual page for your cryptsetup.


David