+/* IPsec IV generation: IVs requirements differ depending of the
+ * encryption mode: IVs must be unpredictable for AES-CBC whereas it can
+ * be predictable but should never be reused with the same key material
+ * for CTR and GCM.
+ * To avoid reusing the same IVs between multiple VPP instances and between
+ * restarts, we use a properly chosen PRNG to generate IVs. To ensure the IV is
+ * unpredictable for CBC, it is then encrypted using the same key as the
+ * message. You can refer to NIST SP800-38a and NIST SP800-38d for more
+ * details. */
+static_always_inline void *
+esp_generate_iv (ipsec_sa_t *sa, void *payload, int iv_sz)
+{
+ ASSERT (iv_sz >= sizeof (u64));
+ u64 *iv = (u64 *) (payload - iv_sz);
+ clib_memset_u8 (iv, 0, iv_sz);
+ *iv = clib_pcg64i_random_r (&sa->iv_prng);
+ return iv;
+}
+