From 03ee804479c23c3a47779346c639005c2a2317e6 Mon Sep 17 00:00:00 2001
From: swrup <swrup@protonmail.com>
Date: Wed, 18 Feb 2026 17:05:40 +0100
Subject: [PATCH]

---
 src/api.ml        |  2 +-
 src/crypto.ml     | 59 ++++++++++++++++++++++++++---------------------
 src/signatures.ml | 33 +++++++++++++-------------
 3 files changed, 50 insertions(+), 44 deletions(-)

diff --git a/src/api.ml b/src/api.ml
index 8a132db1..06a5f729 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -1253,7 +1253,7 @@ module ExchangeKeysResponse = struct
     (* Signature by the exchange master key of the SHA-256 hash of the
        normalized JSON-object of field extensions, if it was set.
        The signature has purpose TALER_SIGNATURE_MASTER_EXTENSIONS. *)
-    extensions_sig: EddsaSignature.t option;
+    extensions_sig: EddsaSignature_untyped.t option;
   }
 
   let jsont =
diff --git a/src/crypto.ml b/src/crypto.ml
index aac1d07d..0ee66fdb 100644
--- a/src/crypto.ml
+++ b/src/crypto.ml
@@ -143,53 +143,60 @@ module EddsaPrivateKey = struct
 end
 
 module EddsaSignature : sig
-  type t
+  type 'a t
 
-  val sign : key:EddsaPrivateKey.t -> string -> t
+  val sign : key:EddsaPrivateKey.t -> to_string:('a -> string) -> 'a -> 'a t
 
   (* Ok () on verification success *)
-  val verify : key:EddsaPublicKey.t -> t -> msg:string -> (unit, string) result
-  val to_octets : t -> string
-  val of_octets : string -> (t, string) result
-  val jsont : t Jsont.t
-  val bin : t Bin.t
-  val caqti : t Caqti_type.t
+  val verify :
+    key:EddsaPublicKey.t ->
+    to_string:('a -> string) ->
+    'a ->
+    'a t ->
+    (unit, string) result
+
+  val to_octets : 'a t -> string
+  val of_octets : string -> ('a t, string) result
+  val jsont : 'a t Jsont.t
+  val bin : 'a t Bin.t
+  val caqti : 'a t Caqti_type.t
 end = struct
   (* transmitted as 64-bytes base32
      binary-encoded objects with just the R and S values *)
-  type t = string
+  type 'a t = string
 
-  (* mirage_crypto: "The result is the concatenation of r and s, as specified in RFC 8032." *)
-  let sign ~key s = Mirage_crypto_ec.Ed25519.sign ~key s
+  (* mirage_crypto:
+     "The result is the concatenation of r and s, as specified in RFC 8032." *)
+  let sign ~key ~to_string r =
+    let s = to_string r in
+    Mirage_crypto_ec.Ed25519.sign ~key s
 
-  let verify ~key s ~msg =
-    let b = Mirage_crypto_ec.Ed25519.verify ~key s ~msg in
+  let verify ~key ~to_string r t =
+    let msg = to_string r in
+    let b = Mirage_crypto_ec.Ed25519.verify ~key t ~msg in
     match b with
-    | false -> Error "signature verification failure: invalid signature"
+    | false -> Error "EddsaSignature verification: invalid signature"
     | true -> Ok ()
 
   let to_octets t = t
 
+  let check_len t =
+    match String.length t = 64 with
+    | false -> Error "EddsaSignature: invalid string length"
+    | true -> Ok ()
+
   let of_octets v =
-    match String.length v = 64 with
-    | false ->
-        Fmt.error "EddsaSignature.of_octets failure: data is not 64 bytes."
-    | true -> Ok v
+    let+ () = check_len v in
+    v
 
   let bin =
     let of_octets_exn t = of_octets t |> Result.get_ok in
     Bin.map (Bin.bytes 64) of_octets_exn to_octets
 
-  let check_size t =
-    match String.length t = 64 with
-    | false -> Error "EddsaSignature: invalid string length"
-    | true -> Ok ()
-
   let jsont =
     let of_b32 s =
       let* t = B32.decode s in
-      let+ () = check_size t in
-      t
+      of_octets t
     in
     let to_b32 = B32.encode in
     Jsont.of_of_string ~kind:"EddsaSignature" of_b32 ~enc:to_b32
@@ -265,7 +272,7 @@ end
 (* some type aliases, just for prettier .mli *)
 type eddsa_priv = EddsaPrivateKey.t
 type eddsa_pub = EddsaPublicKey.t
-type eddsa_sig = EddsaSignature.t
+type 'a eddsa_sig = 'a EddsaSignature.t
 type rsa_priv = RsaPrivateKey.t
 type rsa_pub = RsaPublicKey.t
 type rsa_sig = RsaSignature.t
diff --git a/src/signatures.ml b/src/signatures.ml
index 80cebad6..94db59eb 100644
--- a/src/signatures.ml
+++ b/src/signatures.ml
@@ -6,6 +6,12 @@
    better handling of decoding failure *)
 open Hash
 
+module EddsaSignature_untyped = struct
+  include Crypto.EddsaSignature
+
+  type nonrec t = string t
+end
+
 module Aliases = struct
   module Timestamp = struct
     type t = Time.Timestamp.t
@@ -58,10 +64,10 @@ module Aliases = struct
   module ExchangePrivateKeyP = EddsaPrivateKey
   module MasterPrivateKeyP = EddsaPrivateKey
   module CoinSpendPrivateKeyP = EddsaPrivateKey
-  module MasterSignatureP = EddsaSignature
-  module ReserveSignatureP = EddsaSignature
-  module ExchangeSignatureP = EddsaSignature
-  module CoinSpendSignatureP = EddsaSignature
+  module MasterSignatureP = EddsaSignature_untyped
+  module ReserveSignatureP = EddsaSignature_untyped
+  module ExchangeSignatureP = EddsaSignature_untyped
+  module CoinSpendSignatureP = EddsaSignature_untyped
 end
 
 open Aliases
@@ -157,30 +163,23 @@ end) : sig
   type r = R.r
   type t
 
-  val sign_f : f:(string -> eddsa_sig) -> r -> t
-
-  val verify_f :
-    f:(eddsa_sig -> msg:string -> (unit, string) result) ->
-    t ->
-    r ->
-    (unit, string) result
-
+  val sign : key:EddsaPrivateKey.t -> r -> t
   val jsont : t Jsont.t
   val caqti : t Caqti_type.t
 
-  (* TODO rm *)
+  (* TODO rm? *)
   (* escape hatch, only needed for /keys `exchange_sig` (signature over contatentation of all of the master_sigs) *)
   val to_octets : t -> string
 end = struct
   open Crypto
 
   type r = R.r
-  type t = EddsaSignature.t
+  type t = r EddsaSignature.t
 
-  let sign_f ~f r = f (Bin.to_string R.bin r)
-  let verify_f ~f t r = f t ~msg:(Bin.to_string R.bin r)
+  let to_string : r -> string = Bin.to_string R.bin
+  let sign ~key r = EddsaSignature.sign ~key ~to_string r
   let jsont = EddsaSignature.jsont
-  let caqti : EddsaSignature.t Caqti_type.t = EddsaSignature.caqti
+  let caqti = EddsaSignature.caqti
   let to_octets t = EddsaSignature.to_octets t
 end