csecp256k1

commit d8f52a71f12f7e9c641d20d223c49901065531ad
parent aa6b4415aadbbec9304528849695c4000c897267
Author: Jared Tobin <jared@jtobin.io>
Date:   Sat, 24 Feb 2024 16:37:01 +0400

Add basic ECDH functionality.

I encountered a bunch of problems getting this to work, and I'm still
not sure what resolved them exactly.

I find Cabal's docs to be confusing as to where to place the
-DENABLE_MODULE_ECDH option (it seems to state that it should be under
'cc-options'), but GHC suggests placing it under 'cpp-options', where I
had originally put it.

I originally encountered dyld errors around lazy symbol loading when
trying to call secp256k1's ECDH function in a REPL; the solution may
have been to simply build the package with cabal prior to using the
REPL, as swapping the flags and includes around didn't seem to solve
anything.

Diffstat:
M
secp256k1-sys/lib/Crypto/Secp256k1/Internal.hs
 | 
24
+++++++++++-------------
M
secp256k1-sys/secp256k1-sys.cabal
 | 
11
++++++-----
M
secp256k1-sys/test/Main.hs
 | 
22
++++++++++------------

3 files changed, 27 insertions(+), 30 deletions(-)
diff --git a/secp256k1-sys/lib/Crypto/Secp256k1/Internal.hs b/secp256k1-sys/lib/Crypto/Secp256k1/Internal.hs
@@ -25,7 +25,7 @@ module Crypto.Secp256k1.Internal (
   , secp256k1_ecdsa_signature_serialize_der
 
   -- ecdh
-  -- , secp256k1_ecdh
+  , secp256k1_ecdh
   ) where
 
 import Foreign.Ptr (Ptr)
@@ -155,18 +155,16 @@ foreign import capi
 
 -- ecdh
 
--- XX seems fine, but GHC bails on call
---
--- foreign import capi
---   "secp256k1_ecdh.h haskellsecp256k1_v0_1_0_ecdh"
---   secp256k1_ecdh
---     :: Ptr Context
---     -> Ptr CUChar
---     -> Ptr PubKey64
---     -> Ptr SecKey32
---     -> Ptr a
---     -> Ptr b
---     -> IO CInt
+foreign import capi
+  "secp256k1_ecdh.h haskellsecp256k1_v0_1_0_ecdh"
+  secp256k1_ecdh
+    :: Ptr Context
+    -> Ptr CUChar
+    -> Ptr PubKey64
+    -> Ptr SecKey32
+    -> Ptr a
+    -> Ptr b
+    -> IO CInt
 
 -- schnorr
 
diff --git a/secp256k1-sys/secp256k1-sys.cabal b/secp256k1-sys/secp256k1-sys.cabal
@@ -24,10 +24,14 @@ library
     , bytestring
 
   ghc-options:
-    -optc -Wno-implicit-function-declaration
+      -optc -Wno-implicit-function-declaration
 
   include-dirs:
-    depend/secp256k1/include/
+      depend/secp256k1/include/
+
+  includes:
+      secp256k1.h
+    , secp256k1_ecdh.h
 
   c-sources:
       depend/secp256k1/src/precomputed_ecmult_gen.c
@@ -36,9 +40,6 @@ library
 
   cpp-options:
     -DENABLE_MODULE_ECDH
-    -DENABLE_MODULE_SCHNORRSIG
-    -DENABLE_MODULE_EXTRAKEYS
-    -DENABLE_MODULE_ELLSWIFT
 
 test-suite tests
   type:                exitcode-stdio-1.0
diff --git a/secp256k1-sys/test/Main.hs b/secp256k1-sys/test/Main.hs
@@ -268,18 +268,16 @@ verify_ecdsa tex key msg der = do
         secp256k1_ecdsa_verify tex sip has kep
   pure (suc == 1)
 
--- XX resurrect when ecdh problems solved
---
--- ecdh :: Ptr Context -> BS.ByteString -> BS.ByteString -> IO BS.ByteString
--- ecdh tex pub sec =
---   A.allocaBytes _SEC_BYTES $ \out -> do
---     par <- parse_pubkey tex pub
---     BS.useAsCString par $ \(F.castPtr -> pab) ->
---       BS.useAsCString sec $ \(F.castPtr -> sep) -> do
---         suc <- secp256k1_ecdh tex out pab sep F.nullPtr F.nullPtr
---         when (suc /= 1) $ throwIO Secp256k1Error
---         let key = F.castPtr out
---         BS.packCStringLen (key, _SEC_BYTES)
+ecdh :: Ptr Context -> BS.ByteString -> BS.ByteString -> IO BS.ByteString
+ecdh tex pub sec =
+  A.allocaBytes _SEC_BYTES $ \out -> do
+    par <- parse_pubkey tex pub
+    BS.useAsCString par $ \(F.castPtr -> pab) ->
+      BS.useAsCString sec $ \(F.castPtr -> sep) -> do
+        suc <- secp256k1_ecdh tex out pab sep F.nullPtr F.nullPtr
+        when (suc /= 1) $ throwIO Secp256k1Error
+        let key = F.castPtr out
+        BS.packCStringLen (key, _SEC_BYTES)
 
 -- test inputs