John McDonnell jlmcdonnell

Reverse Engineered VAS Protocol Specification

Research by Grayson Martin
Last Updated 7/8/23

Introduction

Value Added Services (VAS) is the protocol used by NFC capable passes in Apple Wallet. Access to this protocol is heavily restricted on both the device end (a special certificate issued by Apple is required to create these passes) and the reader end (NDA enforced confidentiality). As such, a desire arose to better understand the protocol in order to explore additional use cases and examine its cryptographic integrity. There are gaps in understanding in certain parts of this protocol, however this document contains the minimum necessary understanding to automatically select, read data from, and decrypt a pass.

Importantly, this specification does not enable a malicious actor to read the data from a pass for which they do not have both the reader's private key, and the pass type identifier. Imp

	import org.bouncycastle.util.encoders.Hex;
	import org.web3j.crypto.*;
	import java.math.BigInteger;

	public class ECCExample {

	public static String compressPubKey(BigInteger pubKey) {
	String pubKeyYPrefix = pubKey.testBit(0) ? "03" : "02";
	String pubKeyHex = pubKey.toString(16);
	String pubKeyX = pubKeyHex.substring(0, 64);