Structure and Interpretation of Computer Programmers

Integrating SSH with the keychain on Snow Leopard

Posted on 2010-03-08 by Graham

Not much movement has occurred on projects like SSHKeychain.app or SSHAgent.app in the last couple of years. The reason is that it’s not necessary to use them these days; you can get all of the convenience of keychain-stored SSH passphrases using the built in software. Here’s a guide to using the Keychain to store your pass phrases.

Create the key pair

We’ll use the default key format, which is RSA for SSH protocol 2.0. We definitely want to enter a passphrase, so that if the private key is leaked it cannot be used.

jormungand:~ leeg$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/leeg/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /Users/leeg/.ssh/id_rsa.
Your public key has been saved in /Users/leeg/.ssh/id_rsa.pub.
The key fingerprint is:
ff:ce:0a:f6:ee:0d:e8:a5:aa:56:a0:f3:0b:81:80:cc leeg@jormungand.local
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|+                |
|oE               |
|..  .            |
|. .. .  S        |
|  o.  .  o       |
|  .o .  + +      |
|   .o  o = =     |
|   .oo..oo=o=    |
+-----------------+

If you haven’t seen it before, randomart is not a screenshot from nethack; rather it’s a visual hashing algorithm. Two different public keys are not guaranteed to have different randomart fingerprints, but the chance that they are close enough to pass a quick visual inspection is small.

Deploy the public key to the SSH server

Do this using any available route; I choose to use password-based SSH.

jormungand:~ leeg$ ssh heimdall.local 'cat -  >> .ssh/authorized_keys' < .ssh/id_rsa.pub
Password:

There is no step three

Mac OS X automatically runs ssh-agent, the key-caching service, as a launchd agent. When SSH attempts to negotiate authentication using your key-based identity, you automatically get asked whether you want to store the passphrase in the keychain. Like this:

Now the passphrase is stored in the keychain. Don't believe me? Lookie here:

So your SSH key is protected by the passphrase, and the passphrase is protected by the keychain.

Update: Minor caveat

Of course (and I forgot this :-S), if you use FileVault to protect the home folder on the SSH server, the user's home folder isn't mounted until after you authenticate. This means that the authorized_keys file can't be consulted during negotiation. Once you have logged in once (using your password), subsequent logins will use the keys (as PAM automatically mounts the FileVault volumes the first time, so authorized_keys becomes available).

Posted in Encryption, Keychain, Mac, ssh | 8 Comments

How to hire Graham Lee

Posted on 2010-03-02 by Graham Lee

There are few people who can say that when it comes to Cocoa application security, they wrote the book. In fact, I can think of only one: me. I’ve just put the final draft together for Professional Cocoa Application Security and it will hit the shops in June: click the link to purchase through my Amazon affiliate programme.

Now that the book’s more-or-less complete, I can turn my attention to other interesting projects: by which I mean yours! If your application could benefit from a developer with plenty of security experience and knowledge to share in a pragmatic fashion, or a software engineer who led development of a complex Cocoa application from its legacy PowerPlant origins through Snow Leopard readiness, or a programmer who has worked on performance enhancement in networking systems and low-level daemon code on Darwin and other UNIX platforms, then your project will benefit from an infusion of the Graham Lee magic. Even if you have some NeXTSTEP or OPENSTEP code that needs maintaining, I can help you out: I’ve been using Cocoa for about as long as Apple has.

Send an email to iamleeg <at> securemacprogramming <dot> com and let’s talk about your project. The good news is that for the moment I am available, you probably can afford me[], and I really want to help make your product better. Want to find out more about my expertise? Check out my section on the MDN show, and the MDN security column.

[] It came up at NSConference that a number of devs thought I carry a premium due to the conference appearances, podcasts and other material I produce. Because I believe that honesty is the best policy, I want to come out and say that I don’t charge any such premium. My rates are consistent with other contractors with my level of experience, and I even provide a discounted rate for NGOs and academic institutions.

Posted in book, Business, cocoa, conference, CoreData, iPad, iPhone, Java, kernel, macfuse, mach, nextstep, objc, openstep, UNIX, xcode | 2 Comments

Pre-order professional Mac security books!

Posted on 2010-02-25 by Graham

You too can own a piece of the magic. Professional Cocoa Application Security and Enterprise Mac: Mac OS X Snow Leopard Security are both already in pre-order; use the Amazon affiliate links below if you want to give me a little extra kick-back from the sales of each. You’re most kind :).

Posted in PCAS | Leave a comment

Look what the feds left behind…

Posted on 2010-02-22 by Graham

So what conference was on in this auditorium before NSConference? Well, why don’t we just read the documents they left behind?

Ooops. While there’s nothing at higher clearance than Unrestricted inside, all of the content is marked internal eyes only (don’t worry, feds, I didn’t actually pay too much attention to the content. You don’t need to put me on the no-fly list). There’s an obvious problem though: if your government agency has the word “security” in its name, you should take care of security. Leaving private documentation in a public conference venue does not give anyone confidence in your ability to manage security issues.

Posted in Data Leakage, government, NSConf, Policy, Privacy | Comments Off

More NSConf code signing fun

Posted on 2010-02-21 by Graham

I’ll be talking at the US NSConference on Tuesday, with an extended version of my talk on code signing. I’ll cover how it works, what it does, what it doesn’t do, and what it should do. Importantly, there are still a few seats left for the conference so if you can get to Atlanta by Tuesday, come and watch me talk!

Posted in Codesign, Encryption, iPad, iPhone, Mac, NSConf, Talk | Comments Off

iPh0wnage

Posted on 2010-02-15 by Graham

I just reviewed a blog post I wrote for Graham Cluley a while back, in which I looked at the impact a common vulnerability on the iPhone and Mac would have. I think in the run-up to the iPad’s release, it’s a risk worth bearing in mind.

Posted in iPad, iPhone, Mac, Malware | Leave a comment

Anatomy of a software sales scam

Posted on 2010-02-11 by Graham

A couple of days ago, Daniel Kennett of the KennettNet micro-ISV (in plain talk, a one-man software business) told me that a customer had fallen victim to a scam. She had purchased a copy of his application Music Rescue—a very popular utility for working with iPods—from a vendor but had not received a download or a licence. The vendor had charged her over three times the actual cost of the application, and seemingly disappeared; she approached KennettNet to try and get the licence she had paid for.

Talking to the developer and (via him) the victim, the story becomes more disturbing. The tale all starts when the victim was having trouble with her iPod and iTunes, and contacted Apple support. The support person apparently gave her an address from which to buy Music Rescue, which turned out to be the scammer’s address. Now it’s hard to know what she meant by that, perhaps the support person gave her a URL, or perhaps she was told a search term and accessed the malicious website via a search engine. It would be inappropriate to try and gauge the Apple support staff’s involvement without further details, except to say that the employee clearly didn’t direct her unambiguously to the real vendor’s website. For all we know, the “Apple” staffer she spoke to may not have been from Apple at all, and the scam may have started with a fake Apple support experience. It does seem more likely that she was talking to the real Apple and their staffer, in good faith or otherwise, gave her information that led to the fraudulent website.

The problem is that if you ask a security consultant for a solution to the problem of being scammed in online purchases, they will probably say “only buy software from trusted sources”. Well, this user clearly trusted Apple as a source, and clearly trusted that she was talking to Apple. She probably was, but still ended up the victim of a scam. Where does this leave the advice, and how can a micro-ISV ever sell software if we’re only to go to stores who’ve built up a reputation with us?

Interestingly the app store model, used on the iPhone and iPad, could offer a solution to these problems. By installing Apple as a gateway to app purchases, customers know (assuming they’ve got the correct app store) that they’re talking to Apple, that any purchase is backed by a real application and that Apple have gone to some (unknown) effort to ensure that the application sold is the same one the marketing page on the store claims will be provided. Such a model could prove a convenient and safe way for users to buy applications on other platforms, even were it not to be the exclusive entry point to the platform.

As a final note, I believe that KennettNet has taken appropriate steps to resolve the problem. As close as I can tell the scam website is operated out of the US, making any attempted legal action hard to pursue as the developer is based in the UK. Instead the micro-ISV has offered the victim a discounted licence and assistance in recovering the lost money from her credit card provider’s anti-fraud process. I’d like to thank Daniel for his information and help in preparing this article.

Posted in Phishing, Scam | 1 Comment

Code snippit from NSConference presentation

Posted on 2010-02-11 by Graham

Here’s the code I used to display the code signature status within the sample app at NSConference. You need to be using the 10.6 SDK, and link against Security.framework.

#import <Security/SecCode.h>

- (void)updateSignatureStatus {
    SecCodeRef myCode = NULL;
    OSStatus secReturn = SecCodeCopySelf(kSecCSDefaultFlags, &myCode);
    if (noErr != secReturn) {
        [statusField setIntValue: secReturn];
        return;
    }
    CFMakeCollectable(myCode);
    SecRequirementRef designated = NULL;
    secReturn = SecCodeCopyDesignatedRequirement(myCode,
                                                 kSecCSDefaultFlags,
                                                 &designated);
    if (noErr != secReturn) {
        [statusField setIntValue: secReturn];
        return;
    }
    CFMakeCollectable(designated);
    secReturn = SecCodeCheckValidity(myCode,
                                     kSecCSDefaultFlags,
                                     designated);
    [statusField setIntValue: secReturn];
}

That’s all there is to it. As discussed in my talk, the designated requirement is a requirement baked into the signature seal when the app is signed in Xcode. Application identity is verified by testing whether:

the signature is valid;
the seal is unbroken;
the code satisfies its designated requirement.

Of course there’s nothing to stop you testing code against any requirement you may come up with: the designated requirement just provides “I am the same application that my developer signed”.

Posted in Codesign, NSConf, Talk | Leave a comment

On multitasking

Posted on 2010-02-09 by Graham Lee

TidBITS unwittingly hits the nail on the head while talking about iPad OS multitasking (emphasis added):

It’s easy to imagine wanting to use an iPad to read text in Mobile Safari, copy some text to a Pages document, and send that document to a colleague via Mail. That specific example may turn out to be possible with the current iPhone OS, but it points toward needing more ways for iPad apps to work together in the future.

Let me break down the user’s workflow here:

User reads text in Mobile Safari.

User copies text to a Pages document.

User e-mails that document to a colleague.

The flow of tasks is linear. The user does not need Mail open while reading the text in Safari, nor Safari open while pasting text in Pages. Whether a platform supports multiple simultaneous applications or not, users typically work with one at a time.

The advantage of multiple open apps is that the user can switch tasks really quickly (the other oft-quoted benefit, of being able to see context in multiple places at the same time, is actually a feature of a windowing UI: a different technology, and one that iPhone OS lacks). The disadvantage is a technical one—the operating system must allocate resources to applications that the user isn’t currently working with. The iPhone (and, I presume, the iPad) provides fast task-switching anyway, through its recommendation that app developers retain app state on termination and recover it on launch. The act of moving between apps via the home screen is supposed to feel like switching tasks, even if it’s implemented by a kind of pause-and-resume.

Posted in iPad, iPhone, rant, usability | 4 Comments

Oops. (updated twice)

Posted on 2010-02-05 by Graham

Q: What caused this?

A: this. A Vodafone employee used the corporate Twitter account to post the message:

[@VodafoneUK] is fed up of dirty homo’s and is going after beaver

And as the Vodafone apology attests, this was no hacking attack, instead a case of TGI Friday on the part of an employee. This goes to show that you don’t need an external attacker to ruin your corporate image if you hire the right staff.

Update: according to an article in the Register, the problem tweet was caused by an employee on a different team in the same office misusing an unlocked terminal with access to Vodafone’s Twitter account. ~~They have fired the employee~~, but no word on whether they’re reviewing their security practices. I’m reminded of the solution taken to combat safe-cracking at LANL when Richard Feynman showed how easy it was to open the safes with their confidential contents: don’t let Richard Feynman near the safes.

Update again: Vodafone’s official reply:

On Friday afternoon an employee posted an obscene message from the
official Vodafone UK Twitter profile. The employee was suspended
immediately and we have started an internal investigation. This was not
a hack and we apologise for any offence the tweet may have caused.

This sounds like there’s the potential for their practices to be altered as a result of their “internal investigation”, hopefully they’ll make more information available. It would definitely make an interesting case study on responding to real-world security issues.

Posted in Policy, Twitter | 1 Comment