On Tuesday, September 26, 2017, 8:14:35 AM PDT, \0xDynamite
   <dreamingforward@gmail.com> wrote:
   >>AFAICT, it is UNBREAKABLE if the keysize is at least half the size of
   > your plaintext.
   >
   >> My understanding is that the keysize ought to be as long as the
   message to
   >> be encrypted.
   >Well if they don't know the key length, then using somewhere between
   1/3 and 2/3 should make it unbreakable.
   No, using the full length is necessary.  Using a key length less than
   the full length of the message is very dangerous.
   >> And yes, it is unbreakable...  UNLESS you try to reuse the keys!!!
   >Hmm, but THEY don't know if you re-used them.  So it would take how
   many ciphertexts messages to figure that out?
   You presumably haven't Google-searched "Venona" yet.  I believe it took
   a few thousand.
   See:  https://en.wikipedia.org/wiki/Venona_project
                       Jim Bell
   From that article:
   "Decryption[edit]
   This message traffic, which was encrypted with a one-time pad system,
   was stored and analyzed in relative secrecy by hundreds of
   cryptanalysts over a 40-year period starting in the early 1940s. Due to
   a serious blunder on the part of the Soviets, some of this traffic was
   vulnerable to cryptanalysis. The Soviet company that manufactured the
   one-time pads produced around 35,000 pages of duplicate key numbers, as
   a result of pressures brought about by the German advance on Moscow
   during World War II. The duplication—which undermines the security of a
   one-time system—was discovered and attempts to lessen its impact were
   made by sending the duplicates to widely separated users.[16] Despite
   this, the reuse was detected by cryptologists in the US."