iOS安全：UIWebView访问Https站点防止中间人攻击

2019-11-14 18:08:23

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尽管Https协议能够提供数据的加密、身份的认证等安全服务,但并不是没有漏洞。HTTPS协议安全隐患的存在可能使用户受到各种极具破坏力的网络攻击。其中中间人攻击(Man In The Middle, MITM)就是非常危险的一种攻击方式。

场景分析：假设用户手机接入了不安全的wifi，这时发生了dns被篡改的情况。如用户访问了Https://www.taobao.com, 被跳转到了类似淘宝的钓鱼站点，且该站点用的是真实ca证书，这时用户的账户安全将受到巨大威胁。

这里介绍一个ios中能大大降低此类风险的做法，即公钥证书匹配。

1. 在终端执行，openssl s_client -connect www.taobao.com:443 -showcerts ，获取公钥内容。

 0 s:/C=CN/ST=ZheJiang/L=HangZhou/O=Alibaba (China) Technology Co., Ltd./CN=*.tmall.com   i:/C=BE/O=GlobalSign nv-sa/CN=GlobalSign Organization Validation CA - G2-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

2. 将公钥内容（-----BEGIN CERTIFICATE----- 至-----END CERTIFICATE-----）保存成.PEM格式文件。

3. 执行命令 openssl x509 -inform PEM -outform DER -in cert.pem -out cert.der , 将.pem证书转换成.der格式。

4. 在app工程中，导入生成好的.der证书。

5. 在实现UIWebViewDelegate 的View Controller.h中添加

@interface TargetViewController : UIViewController<UIWebViewDelegate, NSURLConnectionDelegate, NSURLConnectionDataDelegate>

6. 在init方法中添加读取证书的逻辑，并存到self.trustedCerts数组中

        //读取ssl证书信息        if (!hasReadLocalCerts) {            certsFile = [NSMutableArray arrayWithObjects: @"taobao.com.der", nil];            self.trustedCerts = [NSMutableArray array];            for (NSString *file in certsFile) {                NSString *fpath = [[NSBundle mainBundle] pathForResource:file ofType:@"der"];                NSData * cerData = [NSData dataWithContentsOfFile:fpath];                SecCertificateRef certificate = SecCertificateCreateWithData(NULL, (__bridge CFDataRef)(cerData));                [self.trustedCerts addObject:CFBridgingRelease(certificate)];            }            hasReadLocalCerts = YES;        }

7. 在

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request

navigationType:(UIWebViewNavigationType)navigationType

方法中添加https站点的处理逻辑：

    NSURL *url = [request URL];    NSString *schema = [[url scheme] lowercaseString];
　　 //未有过证书验证，将失败的请求纪录下来    if ([schema isEqualToString:@"https"]){        if (!authenticated) {            NSLog(@"Authenticated failed!");            [self.webView stopLoading];            failedRequest = request;            [[[NSURLConnection alloc] initWithRequest:request delegate:self] start] ;                        return NO;        }  　　return YES;      }

8. 实现证书验证

#PRagma mark ------ NSURLConnectionDelegate- (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge{    NSLog(@"Check ssl cert.");        //获取trust object    SecTrustRef trust = challenge.protectionSpace.serverTrust;    SecTrustResultType result;        //这里将之前导入的证书设置成下面验证的Trust Object的anchor certificate    SecTrustSetAnchorCertificates(trust, (__bridge CFArrayRef)self.trustedCerts);        //SecTrustEvaluate会查找前面SecTrustSetAnchorCertificates设置的证书或者系统默认提供的证书，对trust进行验证    OSStatus status = SecTrustEvaluate(trust, &result);    if (status == errSecSuccess &&        (result == kSecTrustResultProceed ||         result == kSecTrustResultUnspecified)) {            //验证成功，生成NSURLCredential凭证cred，告知challenge的sender使用这个凭证来继续连接            NSURLCredential *cred = [NSURLCredential credentialForTrust:trust];            [challenge.sender useCredential:cred forAuthenticationChallenge:challenge];            NSLog(@"SSL cert match!");        }    else {        //验证失败，取消这次验证流程        [challenge.sender cancelAuthenticationChallenge:challenge];        NSLog(@"SSL cert missmatch!");    }        [challenge.sender continueWithoutCredentialForAuthenticationChallenge:challenge];}

#pragma mark ------ NSURLConnectionDataDelegate-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)pResponse {    authenticated = YES;    [connection cancel];
　　 //验证通过，继续执行之前被拦截下来的请求    [self.webView loadRequest:failedRequest];}

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