On 20/09/2023 19:05, Frank Steinmetzger wrote:
In principle, a repeated space character in your passphrase could help
reduce the computational burden of an offline brute force attack, by e.g.
helping an attacker to identify the number of individual words in a
passphrase.
Due to the rotation, the Enigma encoded each subsequent letter differently,
even if the same one repeated, which was (one of) the big strengths of the
Enigma cipher. The flaws were elsewhere, for example that a character could
never be encrypted onto itself due to the internal wiring and certain
message parts were always the same, like message headers and greetings.
And, as always, one of the biggest weaknesses was the operator.
Enigma had three (or in later versions four) rotors. The code book
specified the INITIAL "settings of the day" for those rotors. What was
*supposed* to happen was the operator was supposed to select a random
three/four character string, transmit that string twice, then reset the
rotors to that string before carrying on. So literally no two messages
were supposed to have the same settings beyond the first six characters.
Except that a lot of operators re-used the same characters time and time
again. So if you got a message from an operator you recognised, you
might well know his "seventh character reset". That saved a lot of grief
trying to crack which of the several rotors were "the rotors of the day".
And given that, for a large chunk of the war, the radio operators were
"chatty", you generally got a lot of six-character strings for which you
had a damn good idea what the plain text was.
So even where some of the operators were seriously crypto-aware and
careful, once you'd cracked the rotors and initial settings from the
careless, you could read every message sent by everyone (using those
settings) that day.
Along with other things like RDF giving subs positions away (although
I'm not quite sure how much we had good RDF and how much it was a cover
for us reading their location in status reports), it certainly helped us
loads hunting them down.
Cheers,
Wol
