mobile interface ComputeECDHSharedSecret (ethereum#1219)

* add computeECDHshared secret to the mobile native interface

* Fix type and docs for ComputeECDHSharedSecret

* unmarshal bytes into ecdh public key

accounts/keystore/keystore.go

@@ -44,6 +44,7 @@ import (
 	"github.com/ethereum/go-ethereum/crypto/ecies"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
+	"github.com/wsddn/go-ecdh"
 )
 
 var (
@@ -624,3 +625,26 @@ func zeroKey(k *ecdsa.PrivateKey) {
 		b[i] = 0
 	}
 }
+
+// ComputeECDHSharedSecret computes an ECDH shared secret between the given account's
+// private key and the public key provided. The account has to be unlocked first.
+func (ks *KeyStore) ComputeECDHSharedSecret(a accounts.Account, public []byte) ([]byte, error) {
+	// Look up the key to sign with and abort if it cannot be found
+	ks.mu.RLock()
+	defer ks.mu.RUnlock()
+
+	unlockedKey, found := ks.unlocked[a.Address]
+	if !found {
+		return nil, ErrLocked
+	}
+	gen := ecdh.NewEllipticECDH(crypto.S256())
+	pubKey, ok := gen.Unmarshal(public)
+	if !ok {
+		return nil, errors.New("Could not unmarshal public key from bytes")
+	}
+	secret, err := gen.GenerateSharedSecret(unlockedKey.PrivateKey, pubKey)
+	if err != nil {
+		return nil, err
+	}
+	return secret, nil
+}

mobile/accounts.go

@@ -224,3 +224,9 @@ func (ks *KeyStore) ImportPreSaleKey(keyJSON []byte, passphrase string) (ccount
 	}
 	return &Account{account}, nil
 }
+
+// ComputeECDHSharedSecret computes an ECDH shared secret between the given account's
+// private key and the public key provided. The account has to be unlocked first.
+func (ks *KeyStore) ComputeECDHSharedSecret(a Account, public []byte) ([]byte, error) {
+	return ks.keystore.ComputeECDHSharedSecret(a.account, public)
+}