diff --git a/src/binary_formats.ml b/src/binary_formats.ml
index 2eb61c6b..84836609 100644
--- a/src/binary_formats.ml
+++ b/src/binary_formats.ml
@@ -22,6 +22,61 @@
      exchange and gana master branch are not in sync
      and we should use a specific git tag instead *)
 
+(* -- Crypto keys -- *)
+
+module RsaPublicKey = struct
+  (* libgnuutil format:
+     https://docs.gnunet.org/doxygen/d9/dbe/structGNUNET__CRYPTO__RsaPublicKeyHeaderP.html
+     https://docs.gnunet.org/doxygen/d6/d70/group__libgnunetutil.html#ga9c99a81e8cd649c1c925d23211a0738f
+     https://www.gnupg.org/documentation/manuals/gcrypt/MPI-formats.html
+
+    format:
+     - rsa header
+     - modulus
+     - public_exponent
+
+    integer in big-endian format (MSB first).
+    Leading zeroes are stripped unless they are required to keep a value positive.
+  *)
+  type header = {
+    n_len: int;
+    e_len: int;
+  }
+
+  type t = {
+    header: header;
+    n: Z.t;
+    e: Z.t;
+  }
+
+  (* need to strip leading zeros or something? *)
+  let z_to_bigendian_bits v =
+    let s = Z.to_bits v in
+    let len = String.length s in
+    let s = String.init len (fun i -> s.[len - 1 - i]) in
+    s
+
+  let header_bin =
+    let open Bin in
+    record (fun n_len e_len -> { n_len; e_len })
+    |+ field beint16 (fun t -> t.n_len)
+    |+ field beint16 (fun t -> t.e_len)
+    |> sealr
+
+  let bin =
+    let open Bin in
+    record (fun header n e ->
+        let n = Z.of_bits n in
+        let e = Z.of_bits e in
+        { header; n; e })
+    |+ field header_bin (fun t -> t.header)
+    (* TODO
+         Z.to_bits is in little endian but we need it in big endian *)
+    |+ field cstring (fun t -> z_to_bigendian_bits t.n)
+    |+ field cstring (fun t -> z_to_bigendian_bits t.e)
+    |> sealr
+end
+
 open Include
 
 let int32_size = 4
diff --git a/src/types.ml b/src/types.ml
index 415b6dcb..7ecb2c13 100644
--- a/src/types.ml
+++ b/src/types.ml
@@ -111,13 +111,11 @@ module Amount = struct
     fun s -> parse_string ~consume:Consume.All parse_t s |> Result.join
 end
 
+(* TODO key format *)
 module Eddsa = struct
-  (* TODO test *)
   (* EdDSA and ECDHE public keys always point on Curve25519
      and represented  using the standard 256 bits Ed25519 compact format,
      converted to Crockford Base32. *)
-  (* EdDSA signatures are transmitted as 64-bytes `base32`
-     binary-encoded objects with just the R and S values (base32_ binary-only). *)
   type pub = Mirage_crypto_ec.Ed25519.pub
 
   let pub_of_string s =
@@ -132,6 +130,9 @@ module Eddsa = struct
   let pub_to_string pub =
     pub |> Mirage_crypto_ec.Ed25519.pub_to_octets |> Base_32.encode
 
+  (* TODO is it exactly like in Mirage_crypto_ec.sign:
+     "The result is the concatenation of r and s, as specified in RFC 8032."
+     endianess issue? *)
   (* EdDSA signatures are transmitted as 64-bytes base32
      binary-encoded objects with just the R and S values (base32_ binary-only).
 
@@ -140,13 +141,24 @@ module Eddsa = struct
 end
 
 module Rsa = struct
-  (* TODO
-     GNUNET_CRYPTO custom encode/decode *)
   (* RSA public key converted to Crockford Base32. *)
   type pub = Mirage_crypto_pk.Rsa.pub
 
-  let pub_of_string _s = assert false
-  let pub_to_string _pub = assert false
+  let pub_of_string s =
+    (* TODO bin
+       - no [Bin.of_string] ?
+       - what to do with the int ref? *)
+    let off = ref 0 in
+    let v = Bin.decode Binary_formats.RsaPublicKey.bin s off in
+    let res = Mirage_crypto_pk.Rsa.pub ~n:v.n ~e:v.e in
+    match res with Error (`Msg e) -> Error e | Ok pub -> Ok pub
+
+  let pub_to_string ({ n; e } : Mirage_crypto_pk.Rsa.pub) =
+    let open Binary_formats.RsaPublicKey in
+    let header = { n_len= Z.size n; e_len= Z.size e } in
+    let v = { header; n; e } in
+    let s = Bin.to_string bin v in
+    s
 end
 
 module HashCode = struct