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Consider you lost your laptop with sensitive data and your smart card that contains the private key for your GnuPG and Truecrypt accounts. The smartcard is secured with a 8-digit PIN.


1) Is it possible for an attacker who finds the smartcard to somehow extract the privat-key; resulting in decrypting all sensitive data from GnuPG and Truecrypt?

(a) Consider laboratory circumstances. Further, is it possible to use acid or hightech-laser to melt off the chip shielding and literally 'extract' the private-key with some wires you put there?

(b) Could the attacker basically exploit the PIN verification process with a side channel attack? Imagine the attacker inputs a random PIN and analyzes the side-channel-informations of the smartcard which checks if the PIN is correct. Is that possible?

2) Does it matter what kind of smartcard you use?

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In laboratory conditions, attacks like this are possible:

http://www.cl.cam.ac.uk/~rja14/Papers/faultpap3.pdf

However, most real-world thefts are simple snatch and grab affairs for expensive hardware that produce a few coins for the thief, and encrypted data is rarely at risk. If a dedicated attacker wanted to get your specific encrypted data, they would probably attempt to intercept your use of the machine without actually letting you know they stole it.

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Yes, once they have all the data, they have all the data. Period, end of story.

Now, for the fuzzier part, most smart cards take great care to make it difficult to do so. Some will have a PIN interface that erases the card after N failed attempts. Some will do things such as put powdered aluminum right over the top of the memory chip, so that any attempt to mill your way into the chip to directly read the memory will melt the chip. But it's only designed to increase the difficulty of such exercises.

If you think about it, if you could secure something perfectly, defusing bombs would be a much more difficult art, wouldn't it!

I read an article a few years back that did a side-channel attack on a smart card by measuring the microamp power draw changes as instructions were executed. They were able to back out the AES key by looking at the length of loops that got executed.

In short, the rule is always "if they have physical access to your data, nothing can prevent them from using it." This will hold true up to quantum style cryptography (which could turn the data to noise if you put the wrong password in).

  • Refering to the microamp power attack: If the private-key is stored on smartcard only in encrypted form - PIN is needed to decrypt the private-key. Do you say they can break the PIN-encrypted-key by this kind of attack? If so, wouldnt it be much safer to use no smartcard or any device with a chip that contains key-material (self encrypting drives) that an attacker could exploit to break the whole encryption? – user3200534 Feb 18 '14 at 12:30
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  1. Typically, unless the person who has your card and laptop also knows/guesses your PIN, they should not be able to extract the private key. Once the PIN is guessed, all bets are off because they have passed the two-factor authentication method of something you have (the smart card), and something you know (the PIN). But remember, an 8-digit PIN means a keyspace of 10^8 or 100 million PIN possibilities.

    Most implementations of smart card readers being used to log into a laptop/account should have some sort of protection against a brute force attack, for example, after 3 failed attempts the card reader is locked and human interference is needed to reset the PIN (this happens at my company). It sounds like private keys are typically generated on-board the smart card, so the private key will only exist on the single card. This also means that if you lose the card you will no longer be able to decrypt items encrypted with your public key.

    Some quick searching revealed that differential power or timing analysis could allow an attacker to gain knowledge of the private key (provided something is actively being encrypted or decrypted - I would think this also means they still need the PIN), and using physical corrosives or acid could allow access to the internal processor. (But I don't claim expert advice on these topics.)

  2. I only have experience with contact smart cards, there are also contact-less smart cards and hybrid smart cards. Apparently you can pull some information off of contact-less smart cards, but I would think the private key should still be PIN-protected (and encrypted) and possibly not made available over the air..

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