Subject: Re: [MSEC] problem with keys

From: George Gross <[email-masked]>
Date: Wed, 1 Sep 2004 06:28:33 -0400 (EDT)

Hi Marg,

On Wed, 1 Sep 2004, Marg wrote:

> Hello, i'm searching about a possible solution in reliable multicast

did you mean to say "authenticated" rather than "reliable" in above text?

> communications. what i would like to now is if there is a solution for
> managing keys in this way: is it possible to use several private keys
> associated with a singolar public key?

I am not sure if I understand your question. However, what you are asking
about sounds almost like probablistic encryption, but using it in the
reverse direction for digital signature source authentication. However,
AFAIK, probablistic encryption is a single key pair, not 1 public and N
private keys. Probablistic encryption does have the unusual property that
a single plaintext can be represented by multiple equivalent ciphertexts.

 > I mean, let's consider the case
> of one sender and n receivers. Each receiver has a different private
> key.

I am confused. In this sentence, did you mean to say "sender" rather than
"receiver"?

> If they use their own key to encript a message, can the sender
> use a unique public key to decript the n messages?

When you say "encrypt", I assume you mean a sender encrypts a hash digest
of the multicast message as its source authentication signature, correct?

When you say "decrypt" I'm guessing you really meant to say that the
group's receivers verify the signature of the multicast message?

> Do you know if such
> algorithm exists or is it in phase of study? Thank you Margherita

You can find an introduction to probablistic encryption in Schneir's
"Applied Cryptography" section 23.15. I do not know if it is feasible for
it to be extended for use in your application.

hth,
	George

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From: "Marg" <[email-masked]>
Date: Wed, 1 Sep 2004 12:42:18 +0200

Hello,
i'm searching about a possible solution in reliable multicast communications.
what i would like to now is if there is a solution for managing keys in this way: is it possible to use several private keys associated with a singolar public key?
I mean, let's consider the case of one sender and n receivers.
Each receiver has a different private key.
If they use their own key to encript a message, can the sender use a unique public key to decript the n messages?
Do you know if such algorithm exists or is it in phase of study?
Thank you
Margherita