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."