GPG and multiple recipients

[Don Levey]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Derek Atkins wrote:
> Tom Metro <blu-5a1Jt6qxUNc at public.gmane.org> writes:
> 
>> Dan Ritter wrote:
>>> Don Levey wrote:
>>>> ...gpg generates its own key, encrypts the data with that, and then
>>>> the recipient's public key is used to encrypt the data key...
>>> In fact, this is what always happens, one recipient (R)  or n recipients
>>> R0..Rn. GPG makes a random key K, encrypts your message M with K, then
>>> sends K(M) + R0(K) +... Rn(K).
>> Right...because public key encryption is expensive (CPU intensive), so
>> they use a symmetric cypher to encrypt the payload, and use PKI to
>> encrypt just the symmetric key.
> 
> Not only is public key encryption expensive in terms of CPU, it's also
> extremely limited in the size of the message you can encrypt.  If you
> have a 2048-bit RSA key the message you can encrypt is less than 2K!
> That rules out most messages.  And when PGP first came out people were
> using 512-bit keys.  Imagine being limited to messages of under 60
> bytes.  Not very useful.
> 
> When PGP 2.0 was released in September, 1992, it could only encrypt a
> message to a single recipient, even though it used this same Encrypted
> Session Key (ESK) methodolgy.  Multiple recipient support was added
> shortly thereafter, but I don't recall if that made it into 2.1.1 or
> 2.2 back in '92-93.
> 
Interesting - I didn't know any of this.  Thanks!
 -Don
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFI+J2CiVR8AmYXiFARAkphAJ90pL323D8rnGkcYg1iczdFqV3HggCfYlJs
4FtTTO2SwWYb3CWW3u/0Xlg=
=B9Tj
-----END PGP SIGNATURE-----