prop224: Optimize hs_circ_service_get_intro_circ() digest calculation

[asn]

Our prop224 function for getting an intro circ given its intro object re-calculates the relay identity fpr all the time:

  if (ip->base.is_only_legacy) {
    uint8_t digest[DIGEST_LEN];
    if (BUG(crypto_pk_get_digest(ip->legacy_key, (char *) digest) < 0)) {
      goto end;
    }
    circ = hs_circuitmap_get_intro_circ_v2_service_side(digest);

We could shove that in the hs_service_intro_point_t object as well to cut some digest calculations.

[nickm]

Mark a large number of tickets that I do not think we will do for 0.3.2.

[neel]

Patch (Revision 1)

[neel]

I have created a patch for this patch under the filename b23107-r001.patch. I have also used the cached digest in register_intro_circ().

[dgoulet]

Thanks neel!

Couple of things.

1. We should set the digest right away when creating the legacy key instead of this:

memset(ip->digest, 0, sizeof(ip->digest));

2. We don't need to check for mem is zero when using the legacy IP because if is_only_legacy is set, then digest + legacy_key MUST be set. Actually, considering that we set the digest when an IP is allocated, we don't need this whole if().

3. I would rename the digest to maybe something like legacy_key_digest because there are so many keys in that object that we should just be precise about what digest that is.

Huge thanks!

[neel]

Patch (Revision 2)

[neel]

I have a new patch. The filename is b23107-002.patch.

[asn]

Patch looks good to me.

Please see my branch bug23107 which is neel's patch, with a smaller commit msg, and a tiny amendment to the changes file so that make check-changes does not complain. Here is a PR too: ​https://github.com/torproject/tor/pull/76

Neel thanks for all the code! BTW, since you are a regular contributor now, you should consider forking the torproject tor repo on github and sending us branch names (or PRs) on the tickets instead of attaching .patch files. It's a smoother development procedure :) Thanks again! :)

[dgoulet]

lgtm; I pushed an extra commit to fix an extra white-space left in the header. No biggy!

Merged. Thanks Neel/asn!