diff mbox series

[Openvpn-devel,v4] Reduce number of future epoch keys from 16 to 4

Message ID 20260817142115.28993-1-gert@greenie.muc.de
State New
Headers
Series [Openvpn-devel,v4] Reduce number of future epoch keys from 16 to 4 |

Commit Message

Gert Doering Aug. 17, 2026, 2:21 p.m. UTC 
  From: Arne Schwabe <arne@rfc2549.org>

The calculation in the RFC was wrong and probably influenced
by an older worst case assumption. With the fixed calculation
four future epoch keys should be more than enough even for
100 Gbit/s. So change the number to 4 in OpenVPN as well.

This also reduces the spam about the epoch keys a bit.

Thanks to Ralf Lici for noticing the wrong calculation.

Change-Id: Id3c6681b29026c2920a62a0ea570fd098649e197
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Razvan Cojocaru <razvanc@mailbox.org>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1844
---

This change was reviewed on Gerrit and approved by at least one
developer. I request to merge it to master.

Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1844
This mail reflects revision 4 of this Change.

Acked-by according to Gerrit (reflected above):
Razvan Cojocaru <razvanc@mailbox.org>
diff mbox series

Patch

diff --git a/src/openvpn/crypto_epoch.c b/src/openvpn/crypto_epoch.c
index 54225bf..37933a1 100644
--- a/src/openvpn/crypto_epoch.c
+++ b/src/openvpn/crypto_epoch.c
@@ -308,9 +308,10 @@ 
         free_key_ctx(&co->key_ctx_bi.encrypt);
 
         /* Update the epoch_key for send to match the current key being used.
-         * This is a bit of extra work but since we are a maximum of 16
-         * keys behind, a maximum 16 HMAC invocations are a small price to
-         * pay for not keeping all the old epoch keys around in future_keys
+         * This is a bit of extra work but since we are a maximum of
+         * epoch_data_keys_future_count keys behind (4 by default),
+         * a maximum 4 HMAC invocations are a small price to pay for not
+         * keeping all the old epoch keys around in future_keys
          * array */
         while (co->epoch_key_send.epoch < new_epoch)
         {
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index fd96b85..01e45fd 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -1343,10 +1343,14 @@ 
 init_epoch_keys(struct key_state *ks, struct tls_multi *multi, const struct key_type *key_type,
                 bool server, struct key2 *key2)
 {
-    /* For now we hardcode this to be 16 for the software based data channel
+    /* For now we hardcode this to be 4 for the software based data channel
      * DCO based implementations/HW implementation might adjust this number
-     * based on their expected speed */
-    const uint8_t future_key_count = 16;
+     * based on their expected speed.
+     *
+     * One epoch lasts 910 GiB with 128 byte packets or 78s at 100 GBit/s.
+     * (respectively 1011 GiB and 86s with 1280 byte packets).
+     */
+    const uint8_t future_key_count = 4;
 
     int key_direction = server ? KEY_DIRECTION_INVERSE : KEY_DIRECTION_NORMAL;
     struct key_direction_state kds;