Retrieving an RSA key from a running instance of Apache?

Question

I created an RSA keypair for an SSL certificate and stored the private key in /etc/ssl/private/server.key. Unfortunately this was the only copy of the private key that I had.

Then I accidentally overwrote the file on disk (yes, I know).

Apache is still running and still serving SSL requests, leading me to believe that there may be hope in recovering the private key. (Perhaps there is a symbolic link somewhere in /proc or something?)

This server is running Ubuntu 12.04 LTS.

Answer 1

SUCCESS!

I was able to retrieve the private key. But it wasn't easy. Here's what you need to do:

1. Make sure you do not restart the server or Apache. The game is over at that point. That also means making sure that no monitoring services restart Apache.
2. Grab this file - source code for a tool named passe-partout.

3. Extract the source code and adjust line 9 of Makefile.main to read:

   $(CC) $(CFLAGS) -o $@ $(OBJS) $(LDFLAGS) 

   (Notice that the $(OBJS) and $(LDFLAGS) are reversed in order.)

4. Run ./build.sh.

5. Grab the PID of Apache using:

   service apache2 status 

6. Run the passe-partout command as root:

   sudo passe-partout [PID] 

   ...where [PID] is the value you retrieved in step #5.

7. If the program succeeds, your current directory will have a bunch of extra keys:

   you@server:~# ls id_rsa-0.key id_rsa-1.key id_rsa-2.key 

If all went well (and hopefully it did), one of those keys is the one you need. However, if you had more than one certificate/keyfile in use, then you need to figure out which one it is. Here's how you do that:

First grab a copy of the certificate that matches the signed key. Assuming the file is named server.crt, run the following command:

openssl x509 -noout -modulus -in server.crt | openssl md5 

This will output a value that you will need to match against each of the keys. For each key, run the following command:

openssl rsa -noout -modulus -in id_rsa-0.key | openssl md5 

If one of them matches, you've found the key.

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_{Credit: this article pointed me to passe-partout.}

Answer 2

Most likely it is storing the key in memory, which it does because it needs to keep a copy after it drops privileges and/or decrypts the key using a supplied passphrase.

In theory, you could get it out of the process image if you attached a debugger, though if they are following best practices it will be encrypted against something in memory.

That said, if it happens that it still has it open, /proc/${PID}/fd/${SOMETHING} may be it. If you overwrote it, your key won't be there because the overwriting data will be. If you copied something else into its place (or deleted or unlinked it, or recursively deleted its parent directory), it will be there.