前言
Flutter项目中服务器使用了自签名证书,如果直接使用https请求或者wss请求的话会报证书签名错误。
HandshakeException: Handshake error in client (OS Error:
I/flutter (28959): │ CERTIFICATE_VERIFY_FAILED: unable to get local issuer certificate(handshake.cc:359))
或者
CERTIFICATE_VERIFY_FAILED: self signed certificate in certificate chain(handshake.cc:354))
信任自签名证书
1.忽略证书校验
你可以通过以下步骤忽略证书验证。从而接受自签名证书
首先创建一个class 重写HttpOverrides
class MyHttpOverrides extends HttpOverrides {
HttpClient createHttpClient(SecurityContext context) {
return super.createHttpClient(context)
..badCertificateCallback = (X509Certificate cert, String host, int port) {
//add your certificate verification logic here
return true;
};
}
}
然后在main 方法将MyHttpOverrides 设置成全局的HttpOverrides。
HttpOverrides.global = new DevHttpOverrides();
当系统检测证书有问题时,会通过回调badCertificateCallback让我们有机会接受或拒绝这个错误的证书,当返回true时,表示我们接受这个证书,会继续完成通讯请求,当返回false时,表示我们不接受错误的证书,https通讯将失败。
当然你也可以在badCertificateCallback添加自己的证书校验逻辑。强烈不建议在正式环境将badCertificateCallback直接返回true,因为这样会接受所有的证书,相当于SSL加密层形同虚设,很容易造成中间人攻击。
2.使用本地CA根证书验证服务器证书
我们可以将服务器用来生成自签名证书的CA证书放在本地,设置为受信任的证书,然后用这个证书校验服务器证书。代码如下:
class MyHttpOverrides extends HttpOverrides {
HttpClient createHttpClient(SecurityContext context) {
//加载本地根证书
ByteData data = await rootBundle.load('assets/data/ca-cert.pem');
final SecurityContext clientContext = SecurityContext()
//使用此方法设置受信任根证书
..setTrustedCertificatesBytes(data.buffer.asUint8List())
return super.createHttpClient(context)
..badCertificateCallback = (X509Certificate cert, String host, int port) {
//add your certificate verification logic here
return false;
};
}
}
这种方式能极大提高安全性。
常见问题
CERTIFICATE_VERIFY_FAILED: Hostname mismatch
Flutter ssl默认会检测证书 subject 中的CN字段和请求url 中的host 是否一致。 如果不一致会报这个错误。
如果请求的url时https://baidu.com/tanslate , 那么服务器的证书CN字段必须包含Baidu.com。
很可惜目前基于flutter3.0 没有提供相应的API 去忽略hostname 检测,我们能做的就是在badCertificateCallback 添加自己的校验逻辑,如下:
..badCertificateCallback = (X509Certificate cert, String host, int port) {
if(host=="baidu.com")
return true;
else return false;
};
2.本地CA根证书验证服务器证书时,当服务器证书的签名不对时,会回调到badCertificateCallback, 而其他证书错误也会回调到badCertificateCallback, 如果要如何区分不同的证书错误原因,则需要手动去校验证书的签名等信息。
class MyHttpOverrides extends HttpOverrides {
MyHttpOverrides() {}
HttpClient createHttpClient(SecurityContext? context) {
ByteData data = await rootBundle.load('assets/data/ca-cert.pem');
final SecurityContext clientContext = SecurityContext()
..setTrustedCertificatesBytes(caCertificate);
return super.createHttpClient(clientContext)
..badCertificateCallback = (X509Certificate cert, String host, int port)
//根据根证书校验服务器证书
bool isverify = verifyCertificate(ca_cert, cert.pem);
if (!isverify){
//签名错误
return false;
}
if (currentIp != host) {
return false;
} else {
return true;
}
};
}
}
其中verifyCertificate 方法如下,用到了x509这个package。传送门
import 'dart:convert';
import 'dart:typed_data';
import 'package:x509b/x509.dart' as x509;
import 'package:asn1lib/asn1lib.dart';
import 'flutter_log.dart';
bool verifyCertificate(String caCert, String serverCert) {
// var strX1PublicKeyInfo = "-----BEGIN CERTIFICATE-----\nSOME PUBLIC KEY\n-----END CERTIFICATE-----";
// var strX2Certificate = "-----BEGIN CERTIFICATE-----\nSOME CERTIFICATE\n-----END CERTIFICATE-----";
var x1PublicKey = (x509.parsePem(caCert).single as x509.X509Certificate).publicKey as x509.RsaPublicKey;
var x2Certificate = x509.parsePem(serverCert).single as x509.X509Certificate;
var x2CertificateDER = decodePEM(serverCert);
var asn1Parser = ASN1Parser(x2CertificateDER);
var seq = asn1Parser.nextObject() as ASN1Sequence;
var tbsSequence = seq.elements[0] as ASN1Sequence;
var signature = x509.Signature(Uint8List.fromList(x2Certificate.signatureValue!));
var verifier = x1PublicKey.createVerifier(x509.algorithms.signing.rsa.sha256);
return verifier.verify(tbsSequence.encodedBytes, signature);
}
Uint8List decodePEM(String pem) {
var startsWith = [
'-----BEGIN PUBLIC KEY-----',
'-----BEGIN PRIVATE KEY-----',
'-----BEGIN CERTIFICATE-----',
];
var endsWith = [
'-----END PUBLIC KEY-----',
'-----END PRIVATE KEY-----',
'-----END CERTIFICATE-----'
];
pem=pem.trim();
//HACK
for (var s in startsWith) {
if (pem.startsWith(s)) pem = pem.substring(s.length);
}
for (var s in endsWith) {
if (pem.trim().endsWith(s)) {
Log().i("certificate:substring");
pem = pem.trim().split(s)[0];
}
}
//Dart base64 decoder does not support line breaks
pem = pem.replaceAll('\n', '');
pem = pem.replaceAll('\r', '');
return Uint8List.fromList(base64.decode(pem));
}
作者:星辰大海TT
链接:https://www.jianshu.com/p/5dfb882671a3