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Suppose I have an application which in some way retrieves a client certificate (private/public key pair) at runtime via a secure channel (so I don't have this client certificate at build time).

How can I use this client certificate for client authentication without using keytool and not using some on persistent/ondisk keystore. So I do not want (actually I can't) to import it using a command line keytool?

Actually I want to replicate the functionality done in libcurl. You just set the client certificate (with private key) and your done. It doesn't involve a keystore.

All this has to be done in Java/Android.

Bjorn
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2 Answers2

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You can do it in Java by defining your own KeyManager as described in the JSSE Reference Guide. I can't speak for Android.

user207421
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  • Would it be sufficient to intitialize (init) a KeyManager with a KeyStore object containing my client certificate and private key? I assume I can push my client certificate and private key into that using setCertificateEntry and setKeyEntry. – Bjorn Aug 19 '11 at 09:17
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I just got this working and I dont think you'll be very happy with my answer but it does work :)

So the hard part is to get the pkcs12 certificate you need to perform client authentication, if your certificate is already in pkcs12 then you've got all the hard stuff out of the way and you can refer to the second answer on SSL client authentication in Android to see how to use that certificate.

if you just have a public private key pair and not a pkcs12 certificate then you will need to make one. As far as I could tell there is no way in java/android to create this certificate so you need to use the android NDK and openssl.

if you download the openssl-android project from https://github.com/guardianproject/openssl-android you can use it to build openssl. By default it compiles as a .so shared object but only some of the android devices I tried to run this code on were able to link against libcrypto, so, although im sure there is a better way I went into the Android.mk files and replaced include $(BUILD_SHARED_LIBRARY) with include $(BUILD_STATIC_LIBRARY) in a few places so that I could compile a .a static library.

I then used the info from Android NDK: Link using a pre-compiled static library to link the libcrypto.a I compiled to my native code.

This native code uses openssl to first create an X509 certificate and then uses it to create a PKCS12 file which can be used in the manner I mentioned before located at SSL client authentication in Android

first you need to get your public and private keys into native land as EVP_PKEY pointers which can happen in a variety of ways based on what format your keys are in then you can use the following code to create an X509 certificate

X509 *public_key_cert = X509_new();

X509_gmtime_adj(X509_get_notBefore(public_key_cert),0);
X509_gmtime_adj(X509_get_notAfter(public_key_cert), (long) 60*60*24*365);

X509_set_pubkey(public_key_cert,evp_pub_key);

This creates the most minimally valid X509 certificate which is valid for 1 year. You may want to do other stuff like sign the certificate if you are going to run your own certificate authority, or set any of a large set of headers which contain various bits of information.

next you need to create the pkcs12 certificate using the X509 cert like this:

PKCS12 *pkcs12 = PKCS12_create(password, "Some Sort of Friendly Name", evp_priv_key, public_key_cert, NULL, 0, 0, 0, 0, 0);

password is a char* containing the password which will be used to encrypt the private key using triple-DES

Now that you have a pkcs12 certificate you can go over to SSL client authentication in Android and get client authentication going.

Good Luck!

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Carl Minden
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