small security glitches

[reynt0]

On Fri, 2 Mar 2012, Post Carter wrote:

>  . . . so I think we just have a terminology discrepancy
> here.  What is a bit confusing is using the words encrypted
> vs. decrypted and ciphertext vs. cleartext when we're talking
> about an attacker inserting contents into the message.

I have been reading the exchanges wondering if someone 
would point out what looked like unclear reference
of "encrypted" and "plaintext".  (Amusing, actually. 
Almost like a famous, classic, American comedy joke
involving baseball players' names.)  [P]ost.carter's
"CCCCC" etc below makes things clear, IMHO.

And prompts me to ask a question.  If the receiver
of the tampered-with message sends to the presumed
original sender the "CC" which began originally as
inserted "PP", but sends it encrypted eg with the
original sender's public key, that should not expose
the now-"CC" to the evesdropping attacker, right?  Ie,
the attack would fail if the honest people involved
diligently follow the implicit lead of the original
sender's email, which used encryption, so the reply
to that original encrypted message gets encrypted?

> What I was trying to say was like this...
>  
> 1) Let's say the original sender encryptes a message.  It then looks like
> this where "C" represents some bits of encrypted ciphertext:
>   CCCCC
>  
> 2) Then, the attacker inserts some material of their own into the message,
> denoted here with "P" for plaintext since it has not been subjected to
> encryption.  The message now looks like this:
>   CCCPPCC
>  
> 3) Next, the recipient "decrypts" the message.  Since at its lowest level
> the encryption amounts to XOR'ing the message text against the secret
> key, it essentially results in the flipping of each class of text. "C"
> becomes "P" and "P" becomes "C":
>   PPPCCPP
>  
> 4) In the attack scenario, when the recipient sends the "gibberish" to
> the sender, they are sending the now "encrypted" part of the message
> above denoted by "CC":  PPP -->CC<-- PP
>  
> 5) The attacker intercepts and XOR's the gibberish "CC" against their
> original insertion "PP" from #2 to deduce the key.  Then they can decrypt
> the original "CCCCC" contents from #1.
  . . .