How to use the node-opcua-crypto.decryptBufferWithDerivedKeys function in node-opcua-crypto

// We shall decrypt it with the receiver private key.
        const buf = binaryStream.buffer.slice(binaryStream.length);

        if (!securityTokenData.derivedKeys) {
            console.log("xxxxxxx NO DERIVED KEYX");
            return false;
        }

        const derivedKeys: DerivedKeys = securityTokenData.derivedKeys;

        assert(derivedKeys !== null);
        assert(derivedKeys.signatureLength > 0, " must provide a signature length");

        if (this.securityMode === MessageSecurityMode.SignAndEncrypt) {

            const decryptedBuffer = decryptBufferWithDerivedKeys(buf, derivedKeys);

            // replace decrypted buffer in initial buffer
            decryptedBuffer.copy(binaryStream.buffer, binaryStream.length);

            // adjust length
            binaryStream.buffer = binaryStream.buffer.slice(0, binaryStream.length + decryptedBuffer.length);

            /* istanbul ignore next */
            if (doDebug) {
                debugLog(chalk.cyan("DE-----------------------------"));
                debugLog(hexDump(binaryStream.buffer));
                debugLog(chalk.cyan("-------------------------------"));
            }
        }

        // now check signature ....

if (securityTokenData.securityToken.expired) {
        this._report_error("Security token has expired : tokenId " + securityTokenData.securityToken.tokenId);
        return false;
    }

    // We shall decrypt it with the receiver private key.
    const buf = binaryStream._buffer.slice(binaryStream.length);

    const derivedKeys = securityTokenData.derivedKeys;

    assert(derivedKeys !== null);
    assert(derivedKeys.signatureLength, " must provide a signature length");

    if (this.securityMode === MessageSecurityMode.SIGNANDENCRYPT) {

        const decryptedBuffer = crypto_utils.decryptBufferWithDerivedKeys(buf, derivedKeys);

        // replace decrypted buffer in initial buffer
        decryptedBuffer.copy(binaryStream._buffer, binaryStream.length);

        // adjust length
        binaryStream._buffer = binaryStream._buffer.slice(0, binaryStream.length + decryptedBuffer.length);

        /* istanbul ignore next */
        if (doDebug) {
            debugLog("DE-----------------------------".cyan);
            debugLog(hexDump(binaryStream._buffer));
            debugLog("-------------------------------".cyan);
        }
    }

    // now check signature ....