[strongSwan] nonce Length

[Jafar Al-Gharaibeh]

Hi Andreas,

    Thanks for the quick and thorough answer. I did not find that piece 
of information (nonce size) in the documentation, but as you noted about 
the source code, I did download and dig through the source code 
yesterday and came across the the 32 byte number. Thanks for confirming 
that.

    I also came across nonce plugin configuration:
    nonce {
    }

Is there really any thing configurable here or is that just there for 
completeness?

Kind Regards,
Jafar

On 9/14/2017 1:56 AM, Andreas Steffen wrote:
> Hi Jafar,
>
> section 2.10 of IKEv2 RFC 7296 [1] states that
>
>     Nonces used in IKEv2
>     MUST be randomly chosen, MUST be at least 128 bits in size, and MUST
>     be at least half the key size of the negotiated pseudorandom function
>     (PRF).  However, the initiator chooses the nonce before the outcome
>     of the negotiation is known.  Because of that, the nonce has to be
>     long enough for all the PRFs being proposed.
>
> This is why strongSwan generates nonces with a constant size of 32 bytes
> (256 bits) as defined in nonce_payloads.h [2]
>
>    /**
>     * Nonce size in bytes for nonces sending to other peer.
>     */
>    #define NONCE_SIZE 32
>
> Best regards
>
> Andreas
>
> [1]https://tools.ietf.org/html/rfc7296#section-2.10
> [2]https://git.strongswan.org/?p=strongswan.git;a=blob;f=src/libcharon/encoding/payloads/nonce_payload.h;h=ee8ad17f789ed4fe6a2e3476fc710b79d74885aa;hb=HEAD#l30
>
> On 13.09.2017 20:37, Jafar Al-Gharaibeh wrote:
>> Hi,
>>
>>     What is the default length of the nonce used  to establish and rekey
>> IKE/Child SAs?  is that based on the DH group? and is the length
>> configurable?
>>
>> Thanks,
>> Jafar
> ======================================================================
> Andreas Steffen                         andreas.steffen at strongswan.org
> strongSwan - the Open Source VPN Solution!          www.strongswan.org
> Institute for Networked Solutions
> HSR University of Applied Sciences Rapperswil
> CH-8640 Rapperswil (Switzerland)
> ===========================================================[INS-HSR]==
>