Wednesday, September 17, 2014

the PayPal pot calling the Apple Pay kettle black

so if you haven't heard yet, PayPal took out a full page ad in the New York Times trying to drag Apple Pay's name through the mud based on Apple's unfortunate celebrity nude selfie leak. This despite the fact that PayPal happily hands out your email address to anyone you have a transaction with. In essence, PayPal has been leaking email addresses for years and not doing anything about it, so they shouldn't get to criticize others for leaking personal information.

what's the big deal about email addresses? while it's true that we often have to give every site we do a transaction on an email address, we don't have to give them all the same address. in fact, giving each site a different email address happens to be a pretty good way to avoid spam, but more importantly it's a good way to avoid phishing emails, and that's important where PayPal is concerned because PayPal one of the most phished brands in existence.

unfortunately, because PayPal wants all parties in a transaction to be able to communicate with each other, they do the laziest, most brain-dead thing one can imagine to accomplish this: they hand out your PayPal email address to others, which is pretty much the worst email address to do that with. i have actually had to change the disposable email address i use with PayPal because they are apparently incapable of keeping that address out of the hands of spammers, phishers, and other email-based miscreants. furthermore, i also use their service less because i don't want to have to clean up after their mess.

at some point i may have to start creating disposable PayPal accounts and use prepaid debt cards with them. certainly if i were trying to hide from massive spy agencies then that would be the way to go, but if i'm only concerned with mitigating email-borne threats i really shouldn't have to go to that much trouble. there are other, more intelligent things that PayPal could, even should be doing.

  • they could share the email address of your choosing, rather than the one you registered with their service unconditionally. that way you could provide the same address you probably already provided that other party when you created an account on their site. it shouldn't be too difficult for them to verify that address before sharing it with the other party since they already verify the one you register with.
  • they could offer their own private messaging service so that communication could be done through their servers (which would no doubt aid in conflict resolution).
  • they could provide a disposable email forwarding service such that the party you're interacting with gets a unique {something} address that forwards the mail on to the email address you registered on PayPal with, and once the transaction is completed to everyone's satisfaction the address is deactivated.
they don't do anything like that, however. here's what you can do right now with the facilities PayPal makes available. it's a more painful and less intuitive process than anything proposed above, but it does work.
  1. before you choose to pay for something with PayPal, log into PayPal and add an email address (the one you want shared with the party you're doing a transaction with) to your profile. PayPal limits you to 8 addresses.
  2. confirm the address by opening the confirmation link that was sent to that address
  3. make that address the primary email address for your account
  4. confirm the change in primary email address (if you have a card associated with your PayPal account, PayPal may ask you to enter the full card number)
  5. at this point you can use PayPal to pay for something and the email address that will be shared with the other party is the one you just added to your PayPal account
  6. once you've paid with PayPal you will probably want to log back into PayPal, change the primary email address back to what it originally was (and confirm the change once again) and then remove the address you added for the purposes of your purchase. the reason you'll likely want to do this is because PayPal sends emails to every address it has on record for you, and those duplicate emails will get old fast.
most people aren't even going to be aware that they can do this to keep their real PayPal email address a secret from 3rd parties. as a result all manner of email-borne threats can and eventually will wind up in what would otherwise have been a trusted email inbox. make no mistake, this isn't PayPal providing a way to keep that email address private, this is a way of manipulating PayPal's features to achieve that effect. there are too many unnecessary steps involved for this to be the intended use scenario.

as such, PayPal is leaking a valuable email address by default every time you pay for something. yes Apple's selfie SNAFU was embarrassing to people, and yes if Apple doesn't do something about that now that they're becoming a payment platform it could be not just embarrassing but financially costly for victims, but PayPal is already assisting in similarly costly outcomes right now (not to mention potential malware outcomes) so they really have no right to be criticizing Apple. Apple, at least, is taking steps to correct their problems - what is PayPal doing?

Monday, September 08, 2014

on the strength of authentication factors

i ran across a story on friday about barclays bank rolling out biometric authentication for online banking and wound up starting a debate on twitter that i didn't have time for and couldn't easily fit into a series of tweets even if i did have time. essentially what it came down to was that i don't believe all authentication factors are equally strong and the statement that the barclays system was a "password replacement" raised a red flag for me.

the reason it raised a red flag for me is because single factor biometric authentication is something i've come across before, and not just in an article on the web or even as a user but as a builder. my first job out of university was with a biometric security company, and one of the biggest projects i had while working there was developing an authentication enhancement for windows logon. one of the requests made (and the one i fought the hardest against) was to allow logon with just the biometric. 

here's the problem with this idea - since windows didn't have biometric capabilities built in, the only way to add single factor biometric authentication in was to store more traditional authentication data that windows could accept (such as a password) and then pass that along to windows when the subject's biometric sample matched the registered biometric template. i should note that the article about barclays makes it clear they'll be doing the same thing since they say that barclays won't be storing customer biometric data on their servers. there will have to be a local biometric client that stores more traditional authentication data and passes it on when a biometric match is achieved. storing credentials is not exactly the safest thing in the world. it's not like you can just store a hash of the authentication data in this scenario because you have to be able to present the original, unmodified credentials to the authentication system.

i balked at the idea of making windows less instead of more secure, but i acquiesced when the decision was made to keep the more secure 2 factor mode of operation (without traditional credential storage) in there as well, along with informing the users that biometric-only logon was less secure. 

it's not just less secure because of the credential storage, though, and this is where the twitter debate on friday ventured into. in the course of that job i had the opportunity to examine multiple biometric systems, such as face, voice, iris, etc. and i came away with 2 realizations: 1) the only biometrics that users will ever accept are non-invasive ones (no one wants sensors stuck into them), and 2) that lack of invasiveness makes it relatively easy to steal biometric samples from users, often without them even knowing. fingerprints can be lifted from anything you touch. recordings of your voice can be made without your knowledge. photographs of faces are ubiquitous and a high enough resolution image will capture your iris pattern. 

other authentication factors like passwords and tokens generally rely on restricting access to the authentication data, often through secrecy. when that secrecy is lost, such as when someone takes a photograph of a door key (which is a kind of token) it becomes relatively easy to reproduce the authenticator and gain access to what was being protected. biometrics, especially non-invasive ones, forgo this secrecy under the mistaken belief that reproducing the authenticator is difficult for biometrics. the reality, though, is that you don't have to reproduce a biometric sample, you only have to create an approximation that is good enough to fool the biometric sensor, which often isn't particularly difficult. optical sensors can be fooled with images, audio sensors can be fooled with recordings, the mythbusters once fooled a capacitance sensor by licking a photocopy of a fingerprint.

now hold on, i hear you say, isn't it also really easy to steal passwords? and isn't reproducing that authenticator the easiest of all? it's certainly true that in practice all kinds of things can affect how easy it is for an attacker to become illegitimately authenticated. for that reason i try to look at the upper bound of the strength of the various authentication factors. how strong is a system under ideal conditions, that is where everything goes right and legitimate parties don't make any mistakes.

for passwords, that ideal situation means that the user doesn't accidentally click on anything that would steal his/her password, doesn't get fooled by phishing sites, etc. in short, the attacker can't get the password from the user. it also means the attacker can't get passwords in transit (because that's been properly secured) or a password database from service provider because no vulnerability is found in their system and their employees are likewise careful to avoid making mistakes. under this ideal situation the attacker's only way to succeed in gaining illegitimate entry is to perform an online brute force attack (no, not a dictionary attack, because the user didn't make the mistake of using something from a dictionary) and they'd have to go slow because the ideal provider would have rate-limited failed logon attempts. now you might say this is unrealistic, people make mistakes, and that's true in practice in the aggregate, but it is possible for an individual to do everything right, and it is also possible for attackers to not be able to find any way to attack the provider in order to get the password database. this isn't how strong password protection always is, but rather the ideal we hope to achieve by making our systems secure and avoiding making mistakes, and sometimes in limited cases this is achieved.

for tokens, let's consider the ideal situation to be comparable to that for passwords but on top of that let's consider the strongest token possible (ie. not a door key). let's consider a token that produces one-time-passwords (without any vulnerabilities that would make those passwords easy to predict) so that even brute force attacks become much harder. on the surface this seems even stronger than passwords, but there's a chink in the armour and apple's recent icloud problems are a good example. tokens can be lost or stolen so there needs to be a way to recover from that problem. while our "ideal situation" precludes our user from losing their token, it does not preclude our service provider from providing users with a way to cope with the loss of their tokens. the strongest way to do this is to provide the user with pre-generated one-time-passwords ahead of time. this can work for an individual user who is careful and doesn't make any mistakes but as we've previously seen our "ideal situation" does not extend to the point of saying all users make no mistakes, so the pre-generated one-time-pads are going to fail for reasons such as never being printed out and put in a safe place, or not being able to get to that safe place because the user is traveling, etc. what's a service provider to do then? so far, their best option might be to use traditional passwords as a fall back, and if they do then the token system becomes only as strong as passwords, because although our ideal user didn't lose their token, the provider can't really know that the user didn't lose it (or worse that it was stolen) and has to accept attempts to use the password fall back. while there is room for tokens to be stronger than passwords, the price is that only ideal users will be able to recover in the event of a lost token, and that price may be more than service providers are willing to accept.

for biometrics, we once again consider an ideal user who does nothing wrong, and an ideal service provider who likewise makes no mistakes. in spite of doing nothing wrong the user's voice can still be recorded, their face can still be photographed (in most cultures since facial covering is relatively rare), etc. simply interacting with the world cannot qualify as doing something wrong or making a mistake. acquiring the information necessary to construct a counterfeit authenticator is easy compared to passwords and tokens because no effort is taken to conceal that information and the cultural adjustments needed to change that are beyond what i think would be reasonable to expect. the difficulty in attacking a biometric authentication system boils down to the difficulty in fooling a sensor (or sometimes 2 sensors as people have tried to strengthen fingerprint biometrics with so-called "liveliness tests"), and that difficulty has been consistently overestimated in the past.

this is why i consider biometrics weaker than passwords - because even when everyone does everything right it's still fairly easy to fool the system. as such, when someone (especially a bank) provides people with an authentication system that replaces passwords with biometrics, i think that should raise an alarm. even at that prior job of mine it was conceded that that mode of operation was more about convenience than it was about security. convenience is a double-edged sword, it can make things easier for legitimate users and attackers alike if you aren't careful. using biometrics in a 2 factor authentication system may provide more security than any single factor authentication system can, but biometrics on it's own? there's a reason some people have started saying that your biometric is your username, not your password. don't replace passwords with it (at least not without having someone present to guard against funny business - which isn't an option for online banking).