diff --git a/src/node/net/p2p.ml b/src/node/net/p2p.ml
index 9452db98e..6d8e0de68 100644
--- a/src/node/net/p2p.ml
+++ b/src/node/net/p2p.ml
@@ -174,6 +174,7 @@ type net = {
 and peer = {
   gid : gid ;
   public_key : Crypto_box.public_key ;
+  (*proof_of_work_nonce : Crypto_box.nonce ;*)
   current_nonce : unit -> Crypto_box.nonce ;
   point : point ;
   listening_port : port option ;
diff --git a/src/utils/crypto_box.ml b/src/utils/crypto_box.ml
index 8931436c9..c0cc4248e 100644
--- a/src/utils/crypto_box.ml
+++ b/src/utils/crypto_box.ml
@@ -13,6 +13,7 @@ type secret_key = Sodium.Box.secret_key
 type public_key = Sodium.Box.public_key
 type channel_key = Sodium.Box.channel_key
 type nonce = Sodium.Box.nonce
+type difficulty = int
 
 let random_keypair = Sodium.Box.random_keypair
 let random_nonce = Sodium.Box.random_nonce
@@ -27,3 +28,9 @@ let to_public_key = Sodium.Box.Bigbytes.to_public_key
 let of_public_key = Sodium.Box.Bigbytes.of_public_key
 let to_nonce = Sodium.Box.Bigbytes.to_nonce
 let of_nonce = Sodium.Box.Bigbytes.of_nonce
+let check_proof_of_work pk nonce difficulty = assert false
+let generate_proof_of_work pk difficulty =
+  let rec loop nonce =
+    if check_proof_of_work pk nonce difficulty then nonce
+    else loop (increment_nonce nonce) in
+  loop (random_nonce ())
diff --git a/src/utils/crypto_box.mli b/src/utils/crypto_box.mli
index c1d1b9e47..1bb45c606 100644
--- a/src/utils/crypto_box.mli
+++ b/src/utils/crypto_box.mli
@@ -12,6 +12,7 @@
 type secret_key
 type public_key
 type nonce
+type difficulty
 
 val random_keypair : unit -> secret_key * public_key
 val random_nonce : unit -> nonce
@@ -24,3 +25,5 @@ val to_public_key : MBytes.t -> public_key
 val of_public_key : public_key -> MBytes.t
 val to_nonce : MBytes.t -> nonce
 val of_nonce : nonce -> MBytes.t
+val check_proof_of_work : public_key -> nonce -> difficulty -> bool
+val generate_proof_of_work : public_key -> difficulty -> nonce