FAB-1047 Gossip crypto dependencies

This commit's purpose is to assert the needed crypto abilities
the gossip expects to get from the peer's crypto layer.

FAB-1047

Change-Id: I4a01081eb5aca12278ab7f34d5f1d198c5e315c0
Signed-off-by: Yacov Manevich <yacovm@il.ibm.com>

gossip/api/crypto.go

@@ -0,0 +1,50 @@
+/*
+Copyright IBM Corp. 2016 All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+		 http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package api
+
+import "github.com/hyperledger/fabric/gossip/common"
+
+// MessageCryptoService is the contract between the gossip component and the
+// peer's cryptographic layer and is used by the gossip component to verify,
+// and authenticate remote peers and data they send, as well as to verify
+// received blocks from the ordering service.
+type MessageCryptoService interface {
+
+	// GetPKIidOfCert returns the PKI-ID of a peer's identity
+	GetPKIidOfCert(peerIdentity PeerIdentityType) common.PKIidType
+
+	// VerifyBlock returns nil if the block is properly signed,
+	// else returns error
+	VerifyBlock(signedBlock SignedBlock) error
+
+	// Sign signs msg with this peer's signing key and outputs
+	// the signature if no error occurred.
+	Sign(msg []byte) ([]byte, error)
+
+	// Verify checks that signature is a valid signature of message under a peer's verification key.
+	// If the verification succeeded, Verify returns nil meaning no error occurred.
+	// If peerCert is nil, then the signature is verified against this peer's verification key.
+	Verify(peerIdentity PeerIdentityType, signature, message []byte) error
+}
+
+// PeerIdentityType is the peer's certificate
+type PeerIdentityType []byte
+
+// SignedBlock represents a fabric block that is signed according
+// to the latest block verification policy known to the peer
+type SignedBlock interface {
+}