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Loading a self-signed SSL certificate .crt file and packaging it into a SSLSocketFactory for use with a HttpsURLConnection.
// Usage example...
HttpsURLConnection connection = (HttpsURLConnection) new URL("https://someurl.com").openConnection();
connection.setSSLSocketFactory(buildSslSocketFactory());
private static SSLSocketFactory buildSslSocketFactory(Context context) {
// Add support for self-signed (local) SSL certificates
// Based on http://developer.android.com/training/articles/security-ssl.html#UnknownCa
try {
// Load CAs from an InputStream
// (could be from a resource or ByteArrayInputStream or ...)
CertificateFactory cf = CertificateFactory.getInstance("X.509");
// From https://www.washington.edu/itconnect/security/ca/load-der.crt
InputStream is = context.getResources().getAssets().openAsset("somefolder/somecertificate.crt");
InputStream caInput = new BufferedInputStream(is);
Certificate ca;
try {
ca = cf.generateCertificate(caInput);
// System.out.println("ca=" + ((X509Certificate) ca).getSubjectDN());
} finally {
caInput.close();
}
// Create a KeyStore containing our trusted CAs
String keyStoreType = KeyStore.getDefaultType();
KeyStore keyStore = KeyStore.getInstance(keyStoreType);
keyStore.load(null, null);
keyStore.setCertificateEntry("ca", ca);
// Create a TrustManager that trusts the CAs in our KeyStore
String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
TrustManagerFactory tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
tmf.init(keyStore);
// Create an SSLContext that uses our TrustManager
SSLContext context = SSLContext.getInstance("TLS");
context.init(null, tmf.getTrustManagers(), null);
return context.getSocketFactory();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (KeyStoreException e) {
e.printStackTrace();
} catch (KeyManagementException e) {
e.printStackTrace();
} catch (CertificateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
@alkaaf
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alkaaf commented Apr 8, 2020

@erickok what if i have CA.crt, restClient.crt and restClient.key files.... I am totally confused... :(

CA.crt is used for signing only
restClient.crt is going to loaded by function above
restclient.key is going to used by your server that your android use

@user201610
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user201610 commented Jun 27, 2020

In my android app, I can only see the context.getResources().getAssets().openNonAssetFd(filename) function, not openAsset(filename). This code is very helpful but I still don't know where to put the certificate into. Any directory on an android device? Thanks.

@user201610
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user201610 commented Jun 27, 2020

It is solved:

put the file under "app/src/main/res/raw" with a name such as "mycertificate.crt".

        int identifier = context.getResources().getIdentifier("mycertificate","raw",context.getPackageName());
        InputStream is = context.getResources().openRawResource(identifier);

@Fuji1405116
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Fuji1405116 commented Dec 30, 2020

you can also solve it by :

InputStream is = context.getResources().getAssets().open("certs_server.crt");

where you have your *.crt file in src/main/assets folder.
In the 37th line of the above code, the "context" variable should be renamed to "sslContext"/other as it already exists or needed to call a static method from activity. Everything is just working fine. To understand all the detail and related security issues just follow this official documentation from where the above code snippet has come :

https://developer.android.com/training/articles/security-ssl.html#CommonProblems

@Sargis
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Sargis commented Apr 29, 2021

how can you use crt file in swift code?

@kswat
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kswat commented Jun 17, 2021

Usage says: connection.setSSLSocketFactory(buildSslSocketFactory());

private static SSLSocketFactory buildSslSocketFactory(Context context) {

what is Context ?

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