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*To*: freehaven-dev@seul.org*Subject*: Re: [freehaven-dev] Literature repository, multi-e/single-d cryptoscheme*From*: dmolnar@belegost.mit.edu*Date*: Sun, 7 May 2000 21:52:47 -0400 (EDT)*Delivery-Date*: Sun, 07 May 2000 21:52:53 -0400*In-Reply-To*: <200005071801.OAA16354@w20-575-40.mit.edu>*Reply-To*: freehaven-dev@seul.org*Sender*: owner-freehaven-dev@seul.org

On Sun, 7 May 2000, Michael J Freedman wrote: > A message M is encrypted by keys {e_1 ... e_n} > M can be decrypted by any d_i \element {d_1 ... d_n}, > the corresponding private keys. The most straightforward solution here is to encrypt M a total of n times, each time with a separate public key e_i. Concatenate together and pass around. Then any single d_i can decrypt the corresponding encrypted message and recover the message. I think this is what PGP does. This has message expansion linear in the number of recipients. Does that matter? Well, for large messages it's awful. If we use a hybrid cryptosystem that works like this : 1) Generate random symmetric key K 128 bits long. 2) Encrypt M with K -- E_K(M). 3) Encrypt K with public keys e_1 -- e_n 4) Concatenate encrypted Ks and E_K(M) then we have total size |M| + 128*n bits. Not so bad. Applied Crypto also has a section on this with references -- 22.7 , p.523 (note that "multiple public-key cryptography" actually seems to be discussed afterwards, not before) and protocol I haven't finished reading yet. Thanks, -David

**Follow-Ups**:**Re: [freehaven-dev] Literature repository, multi-e/single-d crypto scheme***From:*Brian T Sniffen <brians@MIT.EDU>

**References**:**[freehaven-dev] Literature repository, multi-e/single-d crypto scheme***From:*Michael J Freedman <mfreed@MIT.EDU>

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