correct issue on ed25519 full session

solving parity mistake with ed25519:
- faulty use of & instead of &&
- magic number used for curve order inside Psig

Author: rdubois-crypto

src/libMPC/SCL_Musig2.mjs

@@ -356,8 +356,8 @@ Psign(secnonce, sk, session_ctx){
     //todo : test range of k1 and k2
     if (this.curve.Has_even_y(R)==false)
       {
-        k1=secp256k1.CURVE.n-k1;
-        k2=secp256k1.CURVE.n-k2;
+        k1=this.order-k1;
+        k2=this.order-k2;
       }
     let d_ = int_from_bytes(sk)
     //todo : test range d

src/libMPC/SCL_ecc.mjs

@@ -92,12 +92,13 @@ export class SCL_ecc
               return true;
         }
         if (this.curve === 'ed25519'){
-            if( (RawHex_Point[0]&&(0x80)==0x80))
+            if( ( (RawHex_Point[0]&(0x80))==0x80))
                 {
                   return false;
                 }
-                else 
+                else { 
                   return true;
+                }
             }
         }
 
@@ -142,8 +143,9 @@ export class SCL_ecc
         return  bytePoint.slice(1,33);//x-only version for noncegen
       }
       if(this.curve=='ed25519') {
-        bytePoint[0]=bytePoint[0]&0x7f;//nullify to force parity bit to 0
-        return bytePoint;
+        let cp=Buffer.from([...bytePoint]);//avoid destruction of input
+        cp[0]=cp[0]&0x7f;//force parity bit to 0
+        return cp;
       }
 
     } 
@@ -172,9 +174,10 @@ export class SCL_ecc
         return P;
       }
       if (this.curve === 'ed25519') {
-        bytePointX[0]=bytePointX[0]&0x7f;//nullify to force parity bit to 0
+        let cp=Buffer.from([...bytePointX]);//avoid destruction of input
+        cp[0]=cp[0]&0x7f;//force parity bit to 0
 
-        return ed25519.ExtendedPoint.fromHex(reverse(bytePointX));
+        return ed25519.ExtendedPoint.fromHex(reverse(cp));
       }
       throw new Error('Unsupported curve');
     }

src/libMPC/test_Musig2.mjs

@@ -371,8 +371,9 @@ function random_fullsession(Curve){
 
     let psigs=[p1,p2];
 
+    console.log("   -Aggregating signature");
     let res=signer.Partial_sig_agg(psigs, session_ctx);
-    console.log("Aggregated signature=", res, res.length);
+    console.log("res", res, res.length);
 
     console.log("  -Final Schnorr verify:");