client/asset: SignMessage hashes message

Update Wallet.SignMessage impls to use an asset-specific hash function
with the provided message.  The resulting signatures will not be
accepted by legacy servers.

client/asset/btc/btc.go

@@ -2184,12 +2184,13 @@ func (btc *baseWallet) SignMessage(coin asset.Coin, msg dex.Bytes) (pubkeys, sig
 		return nil, nil, err
 	}
 	pk := privKey.PubKey()
-	sig, err := privKey.Sign(msg)
+	hash := chainhash.HashB(msg) // legacy servers will not accept this signature!
+	sig, err := privKey.Sign(hash)
 	if err != nil {
 		return nil, nil, err
 	}
 	pubkeys = append(pubkeys, pk.SerializeCompressed())
-	sigs = append(sigs, sig.Serialize())
+	sigs = append(sigs, sig.Serialize()) // DER format serialization
 	return
 }
 

client/asset/btc/btc_test.go

@@ -1862,8 +1862,9 @@ func testSignMessage(t *testing.T, segwit bool, walletType string) {
 	}
 
 	msg := randBytes(36)
+	msgHash := chainhash.HashB(msg)
 	pk := pubKey.SerializeCompressed()
-	signature, err := privKey.Sign(msg)
+	signature, err := privKey.Sign(msgHash)
 	if err != nil {
 		t.Fatalf("signature error: %v", err)
 	}

client/asset/dcr/dcr.go

@@ -1788,9 +1788,10 @@ func (dcr *ExchangeWallet) SignMessage(coin asset.Coin, msg dex.Bytes) (pubkeys,
 		return nil, nil, err
 	}
 	defer priv.Zero()
-	signature := ecdsa.Sign(priv, msg)
+	hash := chainhash.HashB(msg) // legacy servers will not accept this signature!
+	signature := ecdsa.Sign(priv, hash)
 	pubkeys = append(pubkeys, priv.PubKey().SerializeCompressed())
-	sigs = append(sigs, signature.Serialize())
+	sigs = append(sigs, signature.Serialize()) // DER format
 	return pubkeys, sigs, nil
 }
 

client/asset/dcr/dcr_test.go

@@ -1557,7 +1557,8 @@ func TestSignMessage(t *testing.T) {
 
 	msg := randBytes(36)
 	pk := pubKey.SerializeCompressed()
-	signature := ecdsa.Sign(privKey, msg)
+	msgHash := chainhash.HashB(msg)
+	signature := ecdsa.Sign(privKey, msgHash)
 	sig := signature.Serialize()
 
 	node.privWIF, err = dcrutil.NewWIF(privBytes, tChainParams.PrivateKeyID, dcrec.STEcdsaSecp256k1)