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Re: public key



>
>
>
>---- Original Message ----
>From: andreimpopescu@gmail.com
>To: debian-user@lists.debian.org
>Subject: Re: public key
>Date: Sun, 29 Mar 2009 11:33:51 +0300
>
>>On Sun,29.Mar.09, 09:44:33, Daniel Dalton wrote:
>>> Hi,
>>> 
>>> Okay, I've created my public key with gpg, how can I get mutt to
>use it
>>> now so I can sign all messages? And how do I encrypt mail?
>> 
>>From my ~/.mutt/muttrc
>>
>># GPG stuff
>># sign all, encrypting can be selected before sending
>>set crypt_autosign
>>
>># I don't want S/MIME
>>unset crypt_autosmime
>>
>># decrypt without asking
>>set pgp_auto_decode
>>
>># cache the passphrase longer than the default 300 sec.
>>set pgp_timeout=3600
>>
>>and in .gnupg/gpg.conf
>>
>>keyserver x-hkp://subkeys.pgp.net
>>keyserver-options auto-key-retrieve include-disabled include-revoked
>timeout=10
>>use-agent
>>
>>You also need to publish your *public* key to a keyserver, but I
>forgot 
>>how you do it (it's some magic incantation using gpg, see 'man
>gpg').
>>
>>> And when I sign a file, what's stopping someone else from doing:
>>> cp daniel's_signedfile.extention.sign ourfilename.txt.sign
>>
>>You can't mess with a signed text without breaking the signature
>(that's 
>>the whole point of it)
>> 
>>> How can someone verify I created the file and the signiture wasn't
>just
>>> copied and pasted?
>>
>>GOOD verification is a bit more difficult. Right now I could only
>tell 
>>that the signature is *valid*, but there's no way to tell if it was
>you. 
>>
>>Ideally you meet the other party in person and you exchange PGP 
>>signatures. This works for your family or close friends. On a larger
>
>>scale (the Debian project has ~1000 developers and many of them
>never 
>>meet) you need a Web of Trust:
>>
>>I never meet you, but maybe I meet with Ron and exchange signatures
>and 
>>Ron meets you and exchange signatures. If I receive a message from
>you 
>>GPG can tell me that the message was indeed signed with the same
>secret 
>>key that Ron signed.
>>
>>Whether that key really belongs to you is another question. The
>minimum 
>>that should be done when signing the key is some sort of ID check.
>>
>>Regards,
>>Andrei
>>-- 
>>If you can't explain it simply, you don't understand it well enough.
>>(Albert Einstein)
>>
Here's how it works (roughly)
1.  The signature is encrypted with the sender's private key
2.  The entire document (including the encrypted signature) is
encrypted with the receivers public key

Upon reception:
3.  The receiver decrypts the document using his/her private key
(this "guarantees" that the document was not tampered with and was
destined only for the receiver)
4.  The receiver decrypts the signature using the sender's public key
(since only the sender had his/her private key this guarantees that
the document came only from the sender)

All this stuff depends of course on the distribution of public keys
and more importantly the correlation between the public key and the
actual owner of that key.  As someone else pointed out the safest way
is to meet and physically exchange public keys.  Obviously that isn't
always possible.  The alternative is to each send your public key to
a trusted third party who supposedly verifies the owner and
potentially distributes the public key to other trusted key servers.
larry




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