consistent pcp/pbp formats (was: Curve p25519 Replacements for GnuPG?(x2 now) ..)

[Thomas von Dein]

Yuriy,

On Tue, Jan 21, 2014 at 01:32:23PM +0400, Yuriy Kaminskiy wrote:
> Correct format should be:
>   6[1]|temp_keypair.pubkey|len(recipients)[4]|(recipients...)|(secretboxes...)

Let me recap to see if I really got it right:

the sender does:
- generate a random single-use keypair
- generate a random secretbox key
- secretbox the message 32k-wise with the former
- box that key for each recipient
- put into the output the cipher, the recipient stuff
  and the public key part of the random single-use keypair

Is that right?

So, in order to communicate with someone, only user A has to publish her
public key. User B takes it, box()es a message for her, puts his
(random) pk into it and sends it. A then uses the public key included in
the message plus her own secret key, decrypts the message and drops B's
public key afterwards.

Because, usually with curve25519 both A and B had to exchange their
public keys in advance to be able to communicate. The scheme above makes
it a lot easier for users but is it sufficient securitywise?



best,
Tom

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