Re: amcrypt: deprecated key derivation used

Hi,

On topic of low entropy: if you're not already familiar with it, please 
take a look at https://github.com/jirka-h/haveged especially for 
headless systems.

Cheers,
Kees

On 04-05-2022 16:46, Exuvo wrote:
> Ah yes my RANDFILE was probably already created long ago when i 
> initially set up encryption.
>
> From what i have read the random file is not really on most systems as 
> it is only there to help with low entropy systems (ie server that does 
> nothing most of the time).
> Each time openssl runs it uses that file (if specified) for random 
> seeds and at command end it replaces the file with 256 new bytes of 
> randomness for the next invocation.
> It is not needed for decryption.
>
> From the man page the digest is only used to create the real 
> encryption key from the text key you supply. It should not affect 
> speed at all.
> The default digest is sha-256, sha-512 just has more bits. The only 
> thing you would gain is more protection against brute force attacks i 
> think.
>
> Anton "exuvo" Olsson
>    [email protected]
>
> On 2022-05-04 13:02, Stefan G. Weichinger wrote:
>>
>> Am 04.05.22 um 12:46 schrieb Stefan G. Weichinger:
>>> Am 04.05.22 um 11:36 schrieb Exuvo:
>>>> Yeah the included ossl usage is using old key derivation. On my 
>>>> installation i have replaced amcrypt-ossl usage with:
>>>> # cat /etc/amanda/encrypt
>>>> #!/bin/bash
>>>>
>>>> AMANDA_HOME=~amanda
>>>> PASSPHRASE=$AMANDA_HOME/.am_passphrase    # required
>>>> RANDFILE=$AMANDA_HOME/.rnd
>>>> export RANDFILE
>>
>> at first things were failing, the "not found" was misleading me, as I 
>> assumed the wrapper file was missing (I decided to create 
>> "/usr/sbin/exuvo_crypt" ;-) ).
>>
>> Turns out that the RANDFILE was missing, created one by:
>>
>> backup:~$ dd if=/dev/urandom of=.rnd bs=256 count=1
>>
>> I assume I should store/backup that one alongside the encryption 
>> passphrase somewhere? Is it needed for decryption?
>>
>> First dump looks good now, on to some restore tests.
>>
>> btw: I also read of "-md sha512" to speed up ... obsolete when using 
>> "-aes-256-ctr" maybe?
>>
>> If I change encryption now it would be the time to get it right.
>>
>> thanks so far!