[PATCH GnuPG] g10/mainproc: avoid extra hash contexts when decrypting MDC input

[Jussi Kivilinna]

Hello,

Does this patch look ok to push?

-Jussi

ps. Not sure why my email didn't reach mailing-list, I'm not seeing delivery errors at my end.

On 8.2.2022 19.22, Jussi Kivilinna wrote:
> * g10/mainproc.c (mainproc_context): New member
> 'seen_pkt_encrypted_mdc'.
> (release_list): Clear 'seen_pkt_encrypted_mdc'.
> (proc_encrypted): Set 'seen_pkt_encrypted_mdc'.
> (have_seen_pkt_encrypted_aead): Rename to...
> (have_seen_pkt_encrypted_aead_or_mdc): ...this and add check for
> 'seen_pkt_encrypted_mdc'.
> (proc_plaintext): Do not enable extra hash contexts when decrypting
> MDC input.
> --
> 
> Avoiding extra hash contexts speeds up CFB/MDC decryption quite
> a lot. For example, decrypting symmetric-key AES-256 encrypted
> 4 GiB file from RAM to /dev/null sees ~3.4x speed increase on
> AMD Ryzen 5800X:
> 
>   AES256.CFB encryption: 783 MB/s
>   AES256.CFB decryption: 386 MB/s (before)
>   AES256.CFB encryption: 1.3 GB/s (after patch)
> 
> Note, AEAD is still significantly faster:
> 
>   AES256.OCB encryption: 2.2 GB/s
>   AES256.OCB decryption: 3.0 GB/s
> 
> GnuPG-bug-id: T5820
> Signed-off-by: Jussi Kivilinna <jussi.kivilinna at iki.fi>
> ---
>   g10/mainproc.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/g10/mainproc.c b/g10/mainproc.c
> index 1ee5b9a6e..aa028e91b 100644
> --- a/g10/mainproc.c
> +++ b/g10/mainproc.c
> @@ -88,6 +88,7 @@ struct mainproc_context
>     ulong symkeys;    /* Number of symmetrically encrypted session keys.  */
>     struct pubkey_enc_list *pkenc_list; /* List of encryption packets. */
>     int seen_pkt_encrypted_aead; /* PKT_ENCRYPTED_AEAD packet seen. */
> +  int seen_pkt_encrypted_mdc;  /* PKT_ENCRYPTED_MDC packet seen. */
>     struct {
>       unsigned int sig_seen:1;      /* Set to true if a signature packet
>                                        has been seen. */
> @@ -140,6 +141,7 @@ release_list( CTX c )
>     c->any.uncompress_failed = 0;
>     c->last_was_session_key = 0;
>     c->seen_pkt_encrypted_aead = 0;
> +  c->seen_pkt_encrypted_mdc = 0;
>     xfree (c->dek);
>     c->dek = NULL;
>   }
> @@ -547,6 +549,8 @@ proc_encrypted (CTX c, PACKET *pkt)
>   
>     if (pkt->pkttype == PKT_ENCRYPTED_AEAD)
>       c->seen_pkt_encrypted_aead = 1;
> +  if (pkt->pkttype == PKT_ENCRYPTED_MDC)
> +    c->seen_pkt_encrypted_mdc = 1;
>   
>     if (early_plaintext)
>       {
> @@ -823,7 +827,7 @@ proc_encrypted (CTX c, PACKET *pkt)
>   
>   
>   static int
> -have_seen_pkt_encrypted_aead( CTX c )
> +have_seen_pkt_encrypted_aead_or_mdc( CTX c )
>   {
>     CTX cc;
>   
> @@ -831,6 +835,8 @@ have_seen_pkt_encrypted_aead( CTX c )
>       {
>         if (cc->seen_pkt_encrypted_aead)
>   	return 1;
> +      if (cc->seen_pkt_encrypted_mdc)
> +	return 1;
>       }
>   
>     return 0;
> @@ -914,7 +920,7 @@ proc_plaintext( CTX c, PACKET *pkt )
>           }
>       }
>   
> -  if (!any && !opt.skip_verify && !have_seen_pkt_encrypted_aead(c))
> +  if (!any && !opt.skip_verify && !have_seen_pkt_encrypted_aead_or_mdc(c))
>       {
>         /* This is for the old GPG LITERAL+SIG case.  It's not legal
>            according to 2440, so hopefully it won't come up that often.