ipsec: make pre-shared keys harder to misuse

Using pre-shared keys is usually a bad idea, one should use eg. IKEv2
instead, but one does not always have the choice.

For AES-CBC, the IV must be unpredictable (see NIST SP800-38a Appendix
C) whereas for AES-CTR or AES-GCM, the IV should never be reused with
the same key material (see NIST SP800-38a Appendix B and NIST SP800-38d
section 8).
If one uses pre-shared keys and VPP is restarted, the IV counter
restarts at 0 and the same IVs are generated with the same pre-shared
keys materials.

To fix those issues we follow the recommendation from NIST SP800-38a
and NIST SP800-38d:
 - we use a PRNG (not cryptographically secured) to generate IVs to
avoid generating the same IV sequence between VPP restarts. The PRNG is
chosen so that there is a low chance of generating the same sequence
 - for AES-CBC, the generated IV is encrypted as part of the message.
This makes the (predictable) PRNG-generated IV unpredictable as it is
encrypted with the secret key
 - for AES-CTR and GCM, we use the IV as-is as predictable IVs are fine

Most of the changes in this patch are caused by the need to shoehorn an
additional state of 2 u64 for the PRNG in the 1st cacheline of the SA
object.

Type: improvement

Change-Id: I2af89c21ae4b2c4c33dd21aeffcfb79c13c9d84c
Signed-off-by: Benoît Ganne <bganne@cisco.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/src/vnet/ipsec/esp_decrypt.c b/src/vnet/ipsec/esp_decrypt.c
index 1bcc65ca972..827d168f98a 100644
--- a/src/vnet/ipsec/esp_decrypt.c
+++ b/src/vnet/ipsec/esp_decrypt.c
@@ -603,7 +603,7 @@ esp_decrypt_prepare_async_frame (vlib_main_t *vm, vlib_node_runtime_t *node,
   esp_decrypt_packet_data_t *async_pd = &(esp_post_data (b))->decrypt_data;
   esp_decrypt_packet_data2_t *async_pd2 = esp_post_data2 (b);
   u8 *tag = payload + len, *iv = payload + esp_sz, *aad = 0;
-  u32 key_index;
+  const u32 key_index = sa0->crypto_key_index;
   u32 crypto_len, integ_len = 0;
   i16 crypto_start_offset, integ_start_offset = 0;
   u8 flags = 0;
@@ -611,7 +611,6 @@ esp_decrypt_prepare_async_frame (vlib_main_t *vm, vlib_node_runtime_t *node,
   if (!ipsec_sa_is_set_IS_AEAD (sa0))
     {
       /* linked algs */
-      key_index = sa0->linked_key_index;
       integ_start_offset = payload - b->data;
       integ_len = len;
       if (PREDICT_TRUE (sa0->integ_op_id != VNET_CRYPTO_OP_NONE))
@@ -664,8 +663,6 @@ esp_decrypt_prepare_async_frame (vlib_main_t *vm, vlib_node_runtime_t *node,
       else
 	esp_insert_esn (vm, sa0, pd, pd2, &integ_len, &tag, &len, b, payload);
     }
-  else
-    key_index = sa0->crypto_key_index;
 
 out:
   /* crypto */
@@ -1103,7 +1100,7 @@ esp_decrypt_inline (vlib_main_t *vm, vlib_node_runtime_t *node,
 	  is_async = im->async_mode | ipsec_sa_is_set_IS_ASYNC (sa0);
 	}
 
-      if (PREDICT_FALSE (~0 == sa0->thread_index))
+      if (PREDICT_FALSE ((u16) ~0 == sa0->thread_index))
 	{
 	  /* this is the first packet to use this SA, claim the SA
 	   * for this thread. this could happen simultaneously on