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Re: [libvirt] [PATCH] Fix padding of encrypted data



On Tue, May 02, 2017 at 12:02:23PM +0100, Daniel P. Berrange wrote:
> If we are encoding a block of data that is 16 bytes in length,
> we cannot leave it as 16 bytes, we must pad it out to the next
> block boundary, 32 bytes. Without this padding, the decoder will
> incorrectly treat the last byte of plain text as the padding
> length, as it can't distinguish padded from non-padded data.
>
> The problem exhibited itself when using a 16 byte passphrase
> for a LUKS volume
>
>   $ virsh secret-set-value 55806c7d-8e93-456f-829b-607d8c198367 \
>        $(echo -n 1234567812345678 | base64)
>   Secret value set
>
>   $ virsh start demo
>   error: Failed to start domain demo
>   error: internal error: process exited while connecting to monitor: >>>>>>>>>>Len 16
>   2017-05-02T10:35:40.016390Z qemu-system-x86_64: -object \
>     secret,id=virtio-disk1-luks-secret0,data=SEtNi5vDUeyseMKHwc1c1Q==,\
>     keyid=masterKey0,iv=zm7apUB1A6dPcH53VW960Q==,format=base64: \
>     Incorrect number of padding bytes (56) found on decrypted data
>
> Notice how the padding '56' corresponds to the ordinal value of
> the character '8'.
>
> Signed-off-by: Daniel P. Berrange <berrange redhat com>
> ---

ACK

Erik


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