10 ms·

Encryption with Gnu Privacy Guard (GPG)

47 points by triberian 12y ago

calibwam 12y ago
This does not go into the Web of Trust and having your key signed, maybe the most complicated part of PGP, and perhaps also its most important feature.
- noyesno 12y ago
  Agreed - it also fails teach how one should create a revocation certificate.
  - mike-cardwell 12y ago
    No it doesn't. See the section titled "Generating revocation key"
- eli 12y ago
  Web of Trust isn't too useful if you don't know how to sign a message or check a signature.
  - cyphunk 12y ago
    Specifically "check a signature". Even everyone that knows how to sign fail to really check anything. Honestly, if it aint boiled down to a green or red icon then people are going to misuse, assume security when its not, or just click "yes". If you get a new public key for someone, and it's signed by someone else you don't know (most of the time this is the case) are you going to bother to utilise that signature to increase the trust? No. Are you going to assume increased trust somehow regardless? Yes. FAIL. Modify it further, if it is signed by someone you do know what are the chances your UI is going to give you any sort of indication that this is more trusted that other message workflows? And if it doesn't give you any indication (most leave it up to you to check) who's gonna bother to look just passed "your friend <yourfiendsname@company>" ASCII and actually check the key? no one. FAIL. PGP WoT fails miserably.
    - mike-cardwell 12y ago
      I use PGP extensively. However, I haven't bothered with the web of trust, for the same reason I don't publish my address book for everyone to read, privacy.
      - Torgo 12y ago
        I have already run into this at work. I have customers whose keys are publicly available, and others who should not be, and so I cannot effectively use keysigning internally to manage relationships. This is because I don't want to upload every key I know about to a public keyserver. Maybe I am mistaken or maybe there's a way to do that without having multiple keyrings or something, but that's kind of the problem. It's really hard to tell what I would or would not be sharing because there's no "interface" to speak of and I am hardly an expert.
    - brl 12y ago
      btw, how is a person signing a key in the usual WoT model supposed to know whether or not the email address specified in the key uid is actually controlled by the person standing in front of them at the key signing party with passport and key fingerprint in hand? Even if you carefully follow the recommended key signing procedure the binding which actually matters for exchanging encrypted email has very poor validation (or none at all).
      - dublinben 12y ago
        Best practice is to send an encrypted message to that address in order to confirm the owner controls it.
        cyphunk 12y ago
        If you only meant verifying the email as apart of a keysigning party, agreed. Meaning you are looking at their passport and sending an email at the same time. This is better than nothing but wont protect against many directed attacks. For instance, a journalists has to be more careful. Also, in the end if you are sitting in front of each other might as well just verify key fingerprints. Better privacy and security than a simple email verification. If the author meant actually sending someone a email to see that it is indeed owned by them remotely: NO WAY. Does not work: me: "hey, just sending you an email to confirm its really you before sending the secret plans?" them: "yeah, its me. send the plans." That is exactly what WoT tries to solve but can't due to misuse.
  - brl 12y ago
    I don't know if it's very useful even if you do know how to sign keys and verify signatures.
schroedinger23 12y ago
This article also suggests that you should use a 2048 Bit key, and you really shouldn't. Better to go with 4096 Bit. And I guess every CPU is fast enough.
egeozcan 12y ago
There seems to be also a windows implementation: http://www.gpg4win.org/ http://www.gpg4win.org/ (Wondering why the site doesn't use ssl, though) On a related note, I have a hard time understanding why a web site talking about digital security also doesn't have a certificate.
- IgorPartola 12y ago
  Lots of GPG themed sites do not. Notice that key servers provide web access over plain HTTP as well. My best guess is that they do not want to buy into the CA infrastructure and provide security using GPG itself. Also check out MonkeySphere.
  - egeozcan 12y ago
    > My best guess is that they do not want to buy into the CA infrastructure and provide security using GPG itself. This may be true (I really have no idea) but isn't it like travelling on a highway at night with your normal lights turned off because you have a better system based on infrared? After reading about the story of that guy who hacked into a computer by MITMing the notepad++ site, I became even more convinced that all pages must have certificates. Nowadays it's also possible to get a basic ssl cert for free, I can't figure out what the catch is really.
    - IgorPartola 12y ago
      Don't get me wrong, I agree with you. Even my personal 100% static content site is served over HTTPS only. I am just commenting on the pattern that any GPG-themed sites I've seen follow.
vitaluha 12y ago
"To encrypt a File:" gpg -o encrypted_file.gpg –encrypt -r original.file # they didn't put recipient after -r ?
- reedalex01 12y ago
  In this case it will just prompt you for for the recipient. This command is too verbose though. You can type: gpg -e file The output will be file.gpg. It will ask you for a recipient unless you have "default-recipient" or "default-recipient-selt" set in gpg.conf.
kzrdude 12y ago
Did anyone else see reop recently? It's a sort of simple reimagining of easy-to-use public key crypto. http://www.tedunangst.com/flak/post/reop http://www.tedunangst.com/flak/post/reop
ausjke 12y ago
Best blog on using GPG that I have seen. Thanks!
jmnicolas 12y ago
On all the encryption tutorials I found they always assume 2 and only 2 people trying to talk privately. I wonder how would one encrypt a conversation between say 15 people.
- mike-cardwell 12y ago
  Multiple -r's: gpg -e -r recipient1@example.com -r recipient2@example.com That products some ciphertext which can be decrypted by either recipient.
  - jmnicolas 12y ago
    Thank you. Does it weaken the encryption strength ?
    - Cederfjard 12y ago
      No. The symmetric key that is used to encrypt the message is itself encrypted once for every recipient with their respective public keys, so the only difference is filesize (for most intents and purposes negligable). Of course, more recipients equals more targets for an attacker.
      - bmm6o 12y ago
        > Of course, more recipients equals more targets for an attacker. This is especially significant if the recipients have different sized public keys. If you send a message to a 2048-bit key and a 1024-bit key, the message only has 1024 bits of security. So you really do get a weakest link effect.
  - roberto 12y ago
    I learned this the hard way when using gpg+mutt back in 2001. All my Sent mail was being encrypted only with the recipient's key, so I couldn't read it myself. There's an option to also encrypt outgoing email with your own GPG key.

47 points by triberian 12y ago

This does not go into the Web of Trust and having your key signed, maybe the most complicated part of PGP, and perhaps also its most important feature.

noyesno 12y ago
Agreed - it also fails teach how one should create a revocation certificate.
- mike-cardwell 12y ago
  No it doesn't. See the section titled "Generating revocation key"
eli 12y ago
Web of Trust isn't too useful if you don't know how to sign a message or check a signature.
- cyphunk 12y ago
  Specifically "check a signature". Even everyone that knows how to sign fail to really check anything. Honestly, if it aint boiled down to a green or red icon then people are going to misuse, assume security when its not, or just click "yes". If you get a new public key for someone, and it's signed by someone else you don't know (most of the time this is the case) are you going to bother to utilise that signature to increase the trust? No. Are you going to assume increased trust somehow regardless? Yes. FAIL. Modify it further, if it is signed by someone you do know what are the chances your UI is going to give you any sort of indication that this is more trusted that other message workflows? And if it doesn't give you any indication (most leave it up to you to check) who's gonna bother to look just passed "your friend <yourfiendsname@company>" ASCII and actually check the key? no one. FAIL. PGP WoT fails miserably.
  - mike-cardwell 12y ago
    I use PGP extensively. However, I haven't bothered with the web of trust, for the same reason I don't publish my address book for everyone to read, privacy.
    - Torgo 12y ago
      I have already run into this at work. I have customers whose keys are publicly available, and others who should not be, and so I cannot effectively use keysigning internally to manage relationships. This is because I don't want to upload every key I know about to a public keyserver. Maybe I am mistaken or maybe there's a way to do that without having multiple keyrings or something, but that's kind of the problem. It's really hard to tell what I would or would not be sharing because there's no "interface" to speak of and I am hardly an expert.
  - brl 12y ago
    btw, how is a person signing a key in the usual WoT model supposed to know whether or not the email address specified in the key uid is actually controlled by the person standing in front of them at the key signing party with passport and key fingerprint in hand? Even if you carefully follow the recommended key signing procedure the binding which actually matters for exchanging encrypted email has very poor validation (or none at all).
    - dublinben 12y ago
      Best practice is to send an encrypted message to that address in order to confirm the owner controls it.
      - cyphunk 12y ago
        If you only meant verifying the email as apart of a keysigning party, agreed. Meaning you are looking at their passport and sending an email at the same time. This is better than nothing but wont protect against many directed attacks. For instance, a journalists has to be more careful. Also, in the end if you are sitting in front of each other might as well just verify key fingerprints. Better privacy and security than a simple email verification. If the author meant actually sending someone a email to see that it is indeed owned by them remotely: NO WAY. Does not work: me: "hey, just sending you an email to confirm its really you before sending the secret plans?" them: "yeah, its me. send the plans." That is exactly what WoT tries to solve but can't due to misuse.
- brl 12y ago
  I don't know if it's very useful even if you do know how to sign keys and verify signatures.

schroedinger23 12y ago

This article also suggests that you should use a 2048 Bit key, and you really shouldn't. Better to go with 4096 Bit. And I guess every CPU is fast enough.

egeozcan 12y ago

There seems to be also a windows implementation: http://www.gpg4win.org/ http://www.gpg4win.org/ (Wondering why the site doesn't use ssl, though) On a related note, I have a hard time understanding why a web site talking about digital security also doesn't have a certificate.

IgorPartola 12y ago
Lots of GPG themed sites do not. Notice that key servers provide web access over plain HTTP as well. My best guess is that they do not want to buy into the CA infrastructure and provide security using GPG itself. Also check out MonkeySphere.
- egeozcan 12y ago
  > My best guess is that they do not want to buy into the CA infrastructure and provide security using GPG itself. This may be true (I really have no idea) but isn't it like travelling on a highway at night with your normal lights turned off because you have a better system based on infrared? After reading about the story of that guy who hacked into a computer by MITMing the notepad++ site, I became even more convinced that all pages must have certificates. Nowadays it's also possible to get a basic ssl cert for free, I can't figure out what the catch is really.
  - IgorPartola 12y ago
    Don't get me wrong, I agree with you. Even my personal 100% static content site is served over HTTPS only. I am just commenting on the pattern that any GPG-themed sites I've seen follow.

vitaluha 12y ago

"To encrypt a File:" gpg -o encrypted_file.gpg –encrypt -r original.file # they didn't put recipient after -r ?

reedalex01 12y ago
In this case it will just prompt you for for the recipient. This command is too verbose though. You can type: gpg -e file The output will be file.gpg. It will ask you for a recipient unless you have "default-recipient" or "default-recipient-selt" set in gpg.conf.

kzrdude 12y ago

Did anyone else see reop recently? It's a sort of simple reimagining of easy-to-use public key crypto. http://www.tedunangst.com/flak/post/reop http://www.tedunangst.com/flak/post/reop

ausjke 12y ago

Best blog on using GPG that I have seen. Thanks!

jmnicolas 12y ago

On all the encryption tutorials I found they always assume 2 and only 2 people trying to talk privately. I wonder how would one encrypt a conversation between say 15 people.

mike-cardwell 12y ago
Multiple -r's: gpg -e -r recipient1@example.com -r recipient2@example.com That products some ciphertext which can be decrypted by either recipient.
- jmnicolas 12y ago
  Thank you. Does it weaken the encryption strength ?
  - Cederfjard 12y ago
    No. The symmetric key that is used to encrypt the message is itself encrypted once for every recipient with their respective public keys, so the only difference is filesize (for most intents and purposes negligable). Of course, more recipients equals more targets for an attacker.
    - bmm6o 12y ago
      > Of course, more recipients equals more targets for an attacker. This is especially significant if the recipients have different sized public keys. If you send a message to a 2048-bit key and a 1024-bit key, the message only has 1024 bits of security. So you really do get a weakest link effect.
- roberto 12y ago
  I learned this the hard way when using gpg+mutt back in 2001. All my Sent mail was being encrypted only with the recipient's key, so I couldn't read it myself. There's an option to also encrypt outgoing email with your own GPG key.