Re: question about rfc404 support.

[Herbert Xu <herbert@gondor.apana.org.au>]

On Wed, Sep 11, 2013 at 07:16:13PM +0000, Hsieh, Che-Min wrote:
> Herbert:
> 
>   Can you confirm the following. Thanks.
> 
>   Rfc2404 - The Use of HMAC-SHA-1-96 within ESP and AH
>  
>  For the support, I can't find any algorithm to be specified in the .craname of ahash_alg for Rfc2404.
>  
>   From 
> http://www.freebsd.org/cgi/man.cgi?query=setkey&sektion=8
>  it says the following :
> 
>   ALGORITHMS
>      The following list shows the supported algorithms.  The protocol and algorithm are almost completely orthogonal.  The following list of authentication algorithms can be used as aalgo in the -A aalgo of the protocol parameter:
> 
> 	   algorithm	   keylen (bits)       comment
> 	   
> 	   hmac-sha1	   160		   ah: rfc2404
>  
> 
> That leads me to believe, from crypto driver stand point, there is no need to have a new algorithm for hmac-sha-1-96 support.  Instead, the agent SW(such as ipsec) should use  "hmac(sha1)", and do the truncation of digested data from 160 bits to 96 bits.
> 
> I run a quick test. The input file to setkey command is defined as such ----
> 
> flush;
> spdflush;
> add 10.2.243.75 10.2.243.29 ah 0x604 -A hmac-sha1 0x8D967D88F6CAA9D714800AB3D48051D63F73A312;
> add 10.2.243.29 10.2.243.75 ah 0x605 -A hmac-sha1 0x8D967D88F6CAA9D714800AB3D48051D63F73A314;
> spdadd 10.2.243.75 10.2.243.29 any -P in ipsec ah/transport//use;
> spdadd 10.2.243.29 10.2.243.75 any -P out ipsec ah/transport//use;
> 
> 
> I use tcpdump. Clearly I can see 24 bytes of AH header of the ipsec packets.  The header has 12 bytes of fixed information  - Next (1), Ah len (1) ,Reserved (2), Spi (4)  ,Sequence                      (4),  and Auth result.  (12 bytes)
> 
> 
> Can you confirm the above? Thanks.

Yes, see net/xfrm/xfrm_algo.c.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt