func ChannelKey(client, agent HexString, block uint32,
	offeringHash HexString) ([]byte, error) {
	clientAddr, err := HexToAddress(client)
	if err != nil {
		return nil, err
	}

	agentAddr, err := HexToAddress(agent)
	if err != nil {
		return nil, err
	}

	hash, err := base64.URLEncoding.DecodeString(
		strings.TrimSpace(string(offeringHash)))
	if err != nil {
		return nil, err
	}

	blockBytes := Uint32ToBytes(block)

	return crypto.Keccak256(clientAddr.Bytes(),
		agentAddr.Bytes(), blockBytes[:],
		common.BytesToHash(hash).Bytes()), nil
}
func ChannelKey(client, agent HexString, block uint32,
	offeringHash HexString) ([]byte, error) {
	clientAddr, err := HexToAddress(client)
	if err != nil {
		return nil, err
	}

	agentAddr, err := HexToAddress(agent)
	if err != nil {
		return nil, err
	}

	hash, err := base64.URLEncoding.DecodeString(
		strings.TrimSpace(string(offeringHash)))
	if err != nil {
		return nil, err
	}

	blockBytes := Uint32ToBytes(block)

	return crypto.Keccak256(clientAddr.Bytes(),
		agentAddr.Bytes(), blockBytes[:],
		common.BytesToHash(hash).Bytes()), nil
}
// ChannelKey returns the unique channel identifier
// used in a Privatix Service Contract.