On Thu, Mar 26, 2009 at 07:51:15PM +1000, Felipe Alvarez wrote: > _Bob performs symmetric encryption on message with_ > _key "K" (generated randomly). He then encrypts "K" _ > _with Alice's public key, and sends both the symetrically _ > _encrypted message and asymmetrically encrypted key to Alice_ > > Is this what happens during most/some/all of public-key > communications? I had always thought that the message is encrypted > with public key, and decrypted with secret key. I was not aware that > key "K" was encrypted with public key, but message encrypted with > __symmetric_cipher__.
Yes, this is what normally happens with typical usage of gpg. It's called a "hybrid" cipher system. I believe that the reason is that symmetric ciphers are usually more efficient on computing power than asymmetric ones, so you don't really want to be encrypting/decrypting lots of data with an asymmetric cipher. > To help my understanding a little futher, if this does not always > occur, or does not usually occur, when does it occur (not occur)? > Using what ciphers (algorithms)? Typical usage for gpg will be ElGamal for the asymmetric public/private key bit, and AES for the symmetric cipher. -- David Smith | Tel: +44 (0)1454 462380 Home: +44 (0)1454 616963 STMicroelectronics | Fax: +44 (0)1454 462305 Mobile: +44 (0)7932 642724 1000 Aztec West | TINA: 065 2380 GPG Key: 0xF13192F2 Almondsbury | Work Email: dave.sm...@st.com BRISTOL, BS32 4SQ | Home Email: david.sm...@ds-electronics.co.uk
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