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I just started looking into PGP (well, gnupg to be honest). The plan is to both use gpg for communication/email, but also for backups (duplicity), secret stuff

I just started looking into PGP (well, gnupg to be honest). The plan is to both use gpg for communication/email, but also for backups (duplicity), secret stuff/passwords (pass) and authentication (ssh). For that I'm (not affiliated) using a yubikey neo¹ for now. Advantages: - Very easy to set up (works for signing, encrypting, authentication already) - Contains the key material on the 'smart card' In addition my main key is ~elsewhere~: After loading three subkeys on the yubikey I saved and removed my main key from the keychain. This _should_ solve the problem of the airgap in this article? A reasonable way to get access to your data/mail without giving access to your secret key? Things I am confused about/haven't thought through yet/reasons to not switch to use it completely yet: - I'm confused about the key backup solutions here. Keys generated on the smart card cannot be backed up as far as I can see. I have a decent idea of how I'm going to handle my master key (both where and how I'll store it safely), but .. the rest is still not quite clear to me - Mobile. So, if my day to day keys are on this smart card, I cannot read those mails on my mobile. Which .. might be a good thing when we talk about security, but a PITA for my day to day usage. No idea how or if I can solve this one But back to the article: If you're in the "whistle-blowers, activists, spies" category, is the airgap (physically) really required or would a smart card give you the same protection? And the >Mail clients implementing some sort of "Email Manifest protocol" could agree to move critical headers out of the main message and into the encrypted manifest as often as possible line seems overly optimistic in my opinion. Repeat after me: Microsoft Outlook. And .. the introduction is basically PGP/Mime doesn't work everywhere and/or needs plugins first (-> Bad user experience). Is a brand new proposal that wouldn't work anywhere for quite some time really the answer? 1: I got an older release, so no U2F for me, but this is - among other things - a 'smart card'

mike-cardwell 12y ago
> If you're in the "whistle-blowers, activists, spies" category, is the airgap (physically) really required or would a smart card give you the same protection? Smartcard doesn't protect you if your Internet facing machine is compromised. With a separate air gapped machine, you could print out the cipher text from the Internet connected machine, then scan it in/OCR it into the non-Internet connected machine and decrypt it there. Then you could encrypt a response on the non-Internet connected machine, read the cipher text back in to the Internet connected machine via scanning+OCR and send it out.
- TheLoneWolfling 12y ago
  ...Assuming your input stack on your non-internet connected machine is uncompromisable. In practice, this is decidedly not the case. OCR is complex. Your attack surface is not exactly tiny.
  - a1369209993 12y ago
    Good OCR is complex. "Here's a jpeg with 80 lines of 80 characters (from a set of 64 ascii characters chosen for maximum descernability); do your best and I'll run that through a ECC that cuts down to a 32KB chunk." is rather less so. Also, there's no reason your OCR program needs any permissions other than reading a single jpeg and writing a single text file.
    - TheLoneWolfling 12y ago
      You can make the same argument about a non-airgapped computer, though. I don't see any advantage of this over (say) it connected via a dead-simple serial connection.
  - pgeorgi 12y ago
    For computer <-> computer communication, you don't need to print in plain text. Print things as barcodes (or qr or whatever you fancy), then scan them over there - those are much easier and more reliable to parse.
- darklajid 12y ago
  Thanks. My fault. You answered my question, but I asked the wrong one in the first place. Given this sentence in the article: >An "air gap" is a low-tech, widely understood method of protecting secret key material from being compromised. If we send PGP/MIME formatted mail, air-gapping becomes inconvenient to the point of being infeasible. my question was: Wouldn't a smart card - prevent the compromise of one's secret key - therefor allow sending PGP/MIME stuff again quite easily? (your airgap explanation made sense of course)
tokenizerrr 12y ago
Hi. I've recently done something similar with the OpenPGP Smartcard V2[1] (YubiKey seems nicer now, but I don't think they existed when I got mine. In any case, they both seem to perform the same GPG operations, mine can also only hold 3 subkeys, etc). > In addition my main key is ~elsewhere~: After loading three subkeys on the yubikey I saved and removed my main key from the keychain. This _should_ solve the problem of the airgap in this article? A reasonable way to get access to your data/mail without giving access to your secret key? The way I understand it the reason for keeping your main key seperate from the card is so that in case you lose the card you can still issue revocations and issue new keys signed by your master key. The smartcard still contains three seperate secret keys, but does indeed not expose them to the computer. > I'm confused about the key backup solutions here. Keys generated on the smart card cannot be backed up as far as I can see. I have a decent idea of how I'm going to handle my master key (both where and how I'll store it safely), but .. the rest is still not quite clear to me Personally I've opted against having my smartcard generate the keys, because like you said this means it is impossible to extract the subkey used for encryption. Instead I generated the keys on a Raspberry Pi, used paperkey[2] to print them to paper (don't forget to also print some instructions on how to restore, in case you forget or someone else has to do it), and also burned them to a few CDROMs. Then I transferred them to the smartcard, keeping them on the Raspberry Pi's SD card as well, which I keep in a secure location with the CDRoms. > Mobile. So, if my day to day keys are on this smart card, I cannot read those mails on my mobile. Which .. might be a good thing when we talk about security, but a PITA for my day to day usage. No idea how or if I can solve this one I've been wondering if it would be possible to install opengpg on a rooted android phone and then seeing if it were possible to connect it to an usb smartcard reader using an OTG cable, but honestly I think that'd mostly just be a lot of wasted time and effort, and possibly insecure. I tend to carry a chromebook around and instead use that. > But back to the article: If you're in the "whistle-blowers, activists, spies" category, is the airgap (physically) really required or would a smart card give you the same protection? I think a smart card could give you similar protection, if it were to work perfectly. I don't think we can be absolutely certain they aren't backdoored, which is easier to make sure with a basic linux install on a computer that has never seen the internet. Additionally, if you were to use a smart card on a computer attached to the network, the plaintext would exist on that computer at some point which would be a problem if a keylogger or similar were present. [1] http://shop.kernelconcepts.de/product_info.php?products_id=42 http://shop.kernelconcepts.de/product_info.php?products_id=4... [2] http://www.jabberwocky.com/software/paperkey/ http://www.jabberwocky.com/software/paperkey/

mike-cardwell 12y ago

> If you're in the "whistle-blowers, activists, spies" category, is the airgap (physically) really required or would a smart card give you the same protection? Smartcard doesn't protect you if your Internet facing machine is compromised. With a separate air gapped machine, you could print out the cipher text from the Internet connected machine, then scan it in/OCR it into the non-Internet connected machine and decrypt it there. Then you could encrypt a response on the non-Internet connected machine, read the cipher text back in to the Internet connected machine via scanning+OCR and send it out.

TheLoneWolfling 12y ago
...Assuming your input stack on your non-internet connected machine is uncompromisable. In practice, this is decidedly not the case. OCR is complex. Your attack surface is not exactly tiny.
- a1369209993 12y ago
  Good OCR is complex. "Here's a jpeg with 80 lines of 80 characters (from a set of 64 ascii characters chosen for maximum descernability); do your best and I'll run that through a ECC that cuts down to a 32KB chunk." is rather less so. Also, there's no reason your OCR program needs any permissions other than reading a single jpeg and writing a single text file.
  - TheLoneWolfling 12y ago
    You can make the same argument about a non-airgapped computer, though. I don't see any advantage of this over (say) it connected via a dead-simple serial connection.
- pgeorgi 12y ago
  For computer <-> computer communication, you don't need to print in plain text. Print things as barcodes (or qr or whatever you fancy), then scan them over there - those are much easier and more reliable to parse.
darklajid 12y ago
Thanks. My fault. You answered my question, but I asked the wrong one in the first place. Given this sentence in the article: >An "air gap" is a low-tech, widely understood method of protecting secret key material from being compromised. If we send PGP/MIME formatted mail, air-gapping becomes inconvenient to the point of being infeasible. my question was: Wouldn't a smart card - prevent the compromise of one's secret key - therefor allow sending PGP/MIME stuff again quite easily? (your airgap explanation made sense of course)

tokenizerrr 12y ago

Hi. I've recently done something similar with the OpenPGP Smartcard V2[1] (YubiKey seems nicer now, but I don't think they existed when I got mine. In any case, they both seem to perform the same GPG operations, mine can also only hold 3 subkeys, etc). > In addition my main key is ~elsewhere~: After loading three subkeys on the yubikey I saved and removed my main key from the keychain. This _should_ solve the problem of the airgap in this article? A reasonable way to get access to your data/mail without giving access to your secret key? The way I understand it the reason for keeping your main key seperate from the card is so that in case you lose the card you can still issue revocations and issue new keys signed by your master key. The smartcard still contains three seperate secret keys, but does indeed not expose them to the computer. > I'm confused about the key backup solutions here. Keys generated on the smart card cannot be backed up as far as I can see. I have a decent idea of how I'm going to handle my master key (both where and how I'll store it safely), but .. the rest is still not quite clear to me Personally I've opted against having my smartcard generate the keys, because like you said this means it is impossible to extract the subkey used for encryption. Instead I generated the keys on a Raspberry Pi, used paperkey[2] to print them to paper (don't forget to also print some instructions on how to restore, in case you forget or someone else has to do it), and also burned them to a few CDROMs. Then I transferred them to the smartcard, keeping them on the Raspberry Pi's SD card as well, which I keep in a secure location with the CDRoms. > Mobile. So, if my day to day keys are on this smart card, I cannot read those mails on my mobile. Which .. might be a good thing when we talk about security, but a PITA for my day to day usage. No idea how or if I can solve this one I've been wondering if it would be possible to install opengpg on a rooted android phone and then seeing if it were possible to connect it to an usb smartcard reader using an OTG cable, but honestly I think that'd mostly just be a lot of wasted time and effort, and possibly insecure. I tend to carry a chromebook around and instead use that. > But back to the article: If you're in the "whistle-blowers, activists, spies" category, is the airgap (physically) really required or would a smart card give you the same protection? I think a smart card could give you similar protection, if it were to work perfectly. I don't think we can be absolutely certain they aren't backdoored, which is easier to make sure with a basic linux install on a computer that has never seen the internet. Additionally, if you were to use a smart card on a computer attached to the network, the plaintext would exist on that computer at some point which would be a problem if a keylogger or similar were present. [1] http://shop.kernelconcepts.de/product_info.php?products_id=42 http://shop.kernelconcepts.de/product_info.php?products_id=4... [2] http://www.jabberwocky.com/software/paperkey/ http://www.jabberwocky.com/software/paperkey/