Re: [PATCH ipsec-next] xfrm: Drop support for HMAC-RIPEMD-160

[Steffen Klassert]

On Sat, Apr 04, 2026 at 06:15:13PM -0700, Eric Biggers wrote:
> Drop support for HMAC-RIPEMD-160 from IPsec to reduce the UAPI surface
> and simplify future maintenance.  It's almost certainly unused.
> 
> RIPEMD-160 received some attention in the early 2000s when SHA-* weren't
> quite as well established.  But it never received much adoption outside
> of certain niches such as Bitcoin.
> 
> It's actually unclear that Linux + IPsec + HMAC-RIPEMD-160 has *ever*
> been used, even historically.  When support for it was added in 2003, it
> was done so in a "cleanup" commit without any justification [1].  It
> didn't actually work until someone happened to fix it 5 years later [2].
> That person didn't use or test it either [3].  Finally, also note that
> "hmac(rmd160)" is by far the slowest of the algorithms in aalg_list[].
> 
> Of course, today IPsec is usually used with an AEAD, such as AES-GCM.
> But even for IPsec users still using a dedicated auth algorithm, they
> almost certainly aren't using, and shouldn't use, HMAC-RIPEMD-160.
> 
> Thus, let's just drop support for it.  Note: no kconfig update is
> needed, since CRYPTO_RMD160 wasn't actually being selected anyway.
> 
> References:
>   [1] linux-history commit d462985fc1941a47
>       ("[IPSEC]: Clean up key manager algorithm handling.")
>   [2] linux commit a13366c632132bb9
>       ("xfrm: xfrm_algo: correct usage of RIPEMD-160")
>   [3] https://lore.kernel.org/all/1212340578-15574-1-git-send-email-rueegsegger@xxxxxxxxxxx
> 
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>

Applied, thanks a lot Eric!