[Cryptography] New White Paper: GhostLine - Information-Theoretically Secure Multi-Party Chat

[Jerry Leichter]

>> The thing you missed is that knowing any one of the 256 bit blocks in the OTP sequence is terrifyingly easy and can be done by passive eavesdropping.
> 
> To recap, I had previously described a way to generate a pseudo-random OTP versus a truly-random OTP.
> 
> I was of course assuming that the OTP would never be reused, not even one block -- EVER.  That's the primary rule of using an OTP.  In that ideal perfect case, there cannot be a known-plaintext attack.
No, the issue isn’t with reuse  - it’s with known or probable plaintext.

If I use your proposed system to transmit the contents today’s N.Y. Times, someone who just guesses that I’m forwarding the latest news can try the first block, quickly determine the seed, then decrypt the rest of the newspaper - and also the comments you appended to it.  Indeed, this kind of attack was considered so significant prior to the emergence of modern cryptography that when a statement was sent, encrypted, to an embassy for publication, the embassy staff was expected to re-write it before releasing it to deny attackers access to any plaintext.  That’s the issue - not reuse.
                                          -- Jerry