概述

本篇主要讲述在 iOS 环境下如何做 ApplePay 加解密处理，通过这次研究和学习，加深对数据加解密的认识。

注意：正常流程中，加解密不会放在前端处理，需要由服务端处理。

苹果官方对相关数据的结构说明：

https://developer.apple.com/library/content/documentation/PassKit/Reference/PaymentTokenJSON/PaymentTokenJSON.html

国内加密采用的RSA加密，美国区采用的是ECC加密算法。本文只介绍中国区的方式。

1 paymentData获取

在ApplePay sheet 用户验证指纹或密码通过后，会进入系统的下面这个回调方法里：

- (void)paymentAuthorizationViewController:(PKPaymentAuthorizationViewController *)controllerdidAuthorizePayment:(PKPayment *)paymentcompletion:(void (^)(PKPaymentAuthorizationStatus status))completion
{if (payment){NSData * paymentData = payment.token.paymentData;NSError * error = nil ;NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:paymentDataoptions:NSJSONReadingMutableContainerserror:&error];NSLog(@"token: %@", dic);// 通常流程，将 paymentData 传给服务端，由服务端解密数据，在调用银联后端接口发起扣款// ...... UI展示流程处理...... 略}
}

上述代码中的 paymentData 二进制数据是 json数据格式，中包含了苹果加密后的支付信息数据。

例如：对打印出来的数据进行整理可以看到如下：

{"data" : "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","header" : {"publicKeyHash" : "YcmdtTV209LCGVZV99T0lNab3yo0KnudAyBKQPo+5e8=","transactionId":" 41a6eb8dd8602def5f41463ad314e484289258df71ab17b50204ea4795a3db52","wrappedKey" : "l6w4oBmvLF/f/6Gj7idhO5aIFlwZ5qZrqSLxR+mLqsjJqHLf2OUTObn+UOO/Iaupc+nc6Kuz1ZTQbBMG2w6/KC8F07lZTPnCOcHVxxBP03UQn6gNkNV8DLNNqJ9GoBDzbGy/dWgKBBPNEdgA59jKY+8H/XQzvNuZqiFDM4LTr+O3/FdqGy6PxfFHRwRNV15WoKtsfQ91xPf++MI4GoTZSdxpc63ewm/8l5Q81AqnZMH03PMRyu8POT92tl10tg8GRmQFCXMgBm7GM+6nz0tebOoLndspqHbe9xtAGmxzseuFCi4A2q8WaqzPgnQ917bvuUnxNHAkXoPTVIUCsXzxXA=="},"signature" : "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","version" : "RSA_v1"
}

json数据中的每一个字段说明，参见之前提到的苹果文档。文档中的验签流程暂不涉及。

加密的支付信息保存在data中

3 解密步骤

1. 使用ApplePay证书的私钥，对 wrappedKey 进行 RSA 解密，得到 AES加密 key
2. 使用步骤1得到的AES key，对 data 数据进行 AES 解密，得到相关的支付信息。

3.1 获取AES Key

wrappedKey 采用的加密方式为 RSA/ECB/OAEPWithSHA256AndMGF1Padding

系统的iOS10 以前的api，暂时没有找到解密工具方法。（使用第三方 openssl 库应该也可以解密）

最新找到的系统 API 是 iOS 10 提供的。

解密的参考代码如下：

// 获取私钥
// 传入.p12的私钥文件路径和密码
+ (SecKeyRef)getPrivateKeyRefWithContentsOfFile:(NSString *)filePath password:(NSString*)password{NSData *p12Data = [NSData dataWithContentsOfFile:filePath];if (!p12Data) {return nil;}SecKeyRef privateKeyRef = NULL;NSMutableDictionary * options = [[NSMutableDictionary alloc] init];[options setObject: password forKey:(__bridge id)kSecImportExportPassphrase];CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);OSStatus securityError = SecPKCS12Import((__bridge CFDataRef) p12Data, (__bridge CFDictionaryRef)options, &items);if (securityError == noErr && CFArrayGetCount(items) > 0) {CFDictionaryRef identityDict = CFArrayGetValueAtIndex(items, 0);SecIdentityRef identityApp = (SecIdentityRef)CFDictionaryGetValue(identityDict, kSecImportItemIdentity);securityError = SecIdentityCopyPrivateKey(identityApp, &privateKeyRef);if (securityError != noErr) {privateKeyRef = NULL;}}CFRelease(items);return privateKeyRef;
}// 解密数据，返回字符串类型
+ (NSString *)decryptWrappedKey:(NSString *)strprivateKeyWithContentsOfFile:(NSString *)pathpassword:(NSString *)password
{SecKeyRef keyRef = [self getPrivateKeyRefWithContentsOfFile:path password:password];NSData *origionData = [[NSData alloc] initWithBase64EncodedString:str options:0];CFErrorRef errorRef = nil;size_t blockBytes = SecKeyGetBlockSize(keyRef);size_t src_block_size = blockBytes;NSMutableData *resultData = [[NSMutableData alloc] init];for (int idx = 0; idx < origionData.length; idx += src_block_size){NSData *targetData = [[origionData subdataWithRange:NSMakeRange(idx, src_block_size)] copy];CFDataRef targetDataRef = (__bridge CFDataRef)(targetData);CFDataRef dataRef = SecKeyCreateDecryptedData(keyRef, kSecKeyAlgorithmRSAEncryptionOAEPSHA256, targetDataRef, &errorRef);if (dataRef != nil) {NSData *partData = (__bridge NSData *)(dataRef);[resultData appendData:partData];NSLog(@"add %i", idx);}if (errorRef != nil) {NSLog(@"error = %@", errorRef);}NSUInteger leftSize = origionData.length - idx - src_block_size;if ((leftSize < src_block_size) && leftSize > 0) {// 剩余部分也要解密NSData *targetData2 = [[origionData subdataWithRange:NSMakeRange(idx + src_block_size, leftSize)] copy];CFDataRef targetDataRef2 = (__bridge CFDataRef)(targetData2);CFDataRef dataRef2 = SecKeyCreateDecryptedData(keyRef, kSecKeyAlgorithmRSAEncryptionOAEPSHA256, targetDataRef2, &errorRef);if (dataRef2 != nil) {NSData *partData2 = (__bridge NSData *)(dataRef2);[resultData appendData:partData2];NSLog(@"add %i", idx);}break;}}if (resultData.length == 0) {return nil;}else {//2.把二进制数据转换为字符串返回return [resultData base64EncodedStringWithOptions:0];}
}

得到的解密后的key

3.2 解密Data（未完成）

data 字段加密方式为“ AES–128 (id-aes128-GCM 2.16.840.1.101.3.4.1.6), with an initialization vector of 16 null bytes and no associated authentication data.”

注意：是GCM模式，初始向量为16个空字节，并且没有associated authentication data（即所谓的AAD）

ECB 或 CBC 比较常见，暂时没有找到AES-GCM模式的解密API，故打算自己编译 openssl 库，研究openssl 的 API 来解密。

TODO：学习 openssl api 使用，解密 AES 128 GCM 数据。

进阶

目前的加解密只停留在 api 和工具的使用，以后需要进一步了解和学习背后的算法和原理，更进一步提升自己