Why would you want to use a digital envelope? As I understand it, a plain-text message is encrypted using a secret key and then the key is encrypted with the receiver's public key. The encrypted message and the encrypted key is sent as the digital envelope. Now, what I don't understand is why one just don't encrypt the plain-text message with the public key in the first place? The literature I have been reading states that the secret key used to encrypt the message is a one-time key, so wouldn't this render the digital envelope unnecessary? I would understand the purpose of a digital envelope if it was to encrypt the secret key for continued communication, but according to the literature, this does not seem to be the case.
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why one just don't encrypt the plain-text message with the public key in the first place?
If you want to send more than one message, the client and server need a shared secret that they can both use to encrypt and decrypt with.
Speed is very important. Encrypting with a symmetric key is much faster than using a set of asymmetric keys when the plaintext becomes longer.
Bennett
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