[SIGCIS-Members] Question about the Tiltman break in Lorenz cypher (1941)

Mon May 24 10:02:04 PDT 2021

Oh, nice! So Bauer on p 372 is in fact correctly and consistently using
ITA2 naming while the table on p 351 (to which the text refers us) is using
BP naming?

On Mon, 24 May 2021 at 17:15, E. Lazard <Emmanuel.Lazard at dauphine.psl.eu>
wrote:

> Ok, I’ve figured it out…
>
> Remember that the Baudot code encodes 26 letters and 6 control characters.
> Now when giving a list of characters (message, key, ciphertext…), one must
> find a way to express these characters by a symbol, so Bletchley Park had
> their well-known convention. It is NOT the one used in all examples of the
> Tiltman break… So the 5 in the first ciphertext is in fact NOT the 5 used
> at Bletchley Park (which had the meaning of shifting into figures mode). So
> what could it means? It’s one of the ITA2 naming…
>
>  bits  name        ITA2   BP
> 00000 NULL           0    /
> 00010 Carriage Ret.  4    3
> 00100 Space          2    9
> 01000 Line Feed      5    4
> 11011 figures        3    5 or +
> 11111 letters        1    8 or -
>
> Now, what’s very confusing is that the addition table given on page 351 of
> the Copeland book uses the Bletchley Park convention.
>
> So either use the ITA2 naming but then you must use the ITA2 addition
> rules, or use the Bletchley Park naming for both, but do not mix them!
>
> Emmanuel
>
>
>
>
> Le 24 mai 2021 à 16:27, Mark Priestley <m.priestley at gmail.com> a écrit :
>
> Emmanuel -
>
> I don't know if the cyphertexts have been wrongly transcribed or not, but
> for sure Friedrich Bauer made a slip when he added them together, as I
> described in my earlier post (did you see that?).
>
> If the originals exists, they might be in the Bletchley Park archives.
> Their website https://bletchleypark.org.uk/ has some information about
> their collections and archives, and contact details.
>
> Best
> Mark
>
>
> On Mon, 24 May 2021 at 14:41, E. Lazard <Emmanuel.Lazard at dauphine.psl.eu>
> wrote:
>
>> Many thanks for your answers.
>>
>> Le 24 mai 2021 à 04:38, thomas.haigh at gmail.com a écrit :
>>
>> I wonder if the problem is in part that Copeland got the teleprinter
>> character set wrong. Some years ago I was working from the version given in
>> his appendix when trying to understand the quirks in the interaction of
>> German and the teleprinter code that explained why the deltas between the
>> bit patterns for successive characters were both much more likely to be 0
>> than 1. That is what underpinned Tutte's method, used by Colossus, which
>> exploited the fact that the deltas between successive characters were not
>> fully scrambled by the Lorenz equipment. So there was a clear statistical
>> signature that marked the correct positions for the first two "Chi wheels."
>> (That analysis underpinned my attempt to give an accurate but
>> non-mathematical account of the process in
>> https://cacm.acm.org/magazines/2017/1/211102-colossal-genius/fulltext).
>>
>> I was having some difficulty in squaring tables in archival reports
>> giving the most common two letter sequences in the encoded messages with
>> the bit patterns for the deltas between them. Then I realized, or my
>> collaborator Mark Priestley pointed out, that the discrepancies were caused
>> by errors in the teleprinter alphabet Copeland included as appendix 2 on
>> pages 248-9. Five years on I can’t remember if there was just one error or
>> several. But I do remember that the frequency of EI in the plaintext was
>> very high so I just  rechecked that his entries for those letters. I see
>> that the code Copeland gives for I (oxxox) does not match the one given at
>>  https://en.wikipedia.org/wiki/Baudot_code. The other clue is that
>> Copeland has the same bit pattern in successive lines, identified first as
>> coding P and then as coding I. They can't both be right.
>>
>> Looking at the
>> https://billtuttememorial.org.uk/codebreaking/teleprinter-code/ page
>> that Emmanuel mentions, I notice a similarly blatant error: the page
>> identifies both M and N as being coded by (ooxxx). Which doesn't match
>> Copeland or Wikipedia. So it appears that both the Tutte fan site and the
>> Copeland book present incorrect teleprinter alphabets.
>>
>>
>> I’ve checked in my copy of the Copeland book and indeed, the I code
>> isn’t correct:  it’s given as •xx•x (same as P) but it should be •xx••.
>> It’s the only mistake in the book (concerning the Baudot code) and it
>> doesn’t solve my issue where I isn’t involved…
>>
>>
>>  Hence Emanuel shouldn't discount the possibility that the cyphertexts
>> are correct but the teleprinter code to bit conversions are wrongly given
>> in both the sources he is relying on. Having said that, given the rather
>> low standards of proofreading we're seeing here it wouldn't shock me if the
>> cypher text sequences were also given wrongly in Copeland and copied from
>> one website to another with errors included. I don't have time to check
>> back to primary sources, but if I was doing serious work on the
>> technicalities of this, I'd either dig into the archival sources or at
>> least work as much as possible from Reeds, James A., Whitfield Diffie, and
>> J V Field. Breaking Teleprinter Ciphers at Bletchley Park. An Edition of
>> General Report on Tunny With Emphasis on Statistical Methods (1945).
>> Piscataway, NJ: IEEE Press/Wiley, 2015  (
>> https://www.amazon.com/Breaking-Teleprinter-Ciphers-Bletchley-Park/dp/0470465891).
>> This is a heavily annotated and supplemented reprint of a formerly secret
>> report written as the operation was being wound down at the end of the war.
>> Chapter 41-44 give a thorough description of the original methods used
>> prior to mechanization. (Though not, as far as I can see on a quick look,
>> the full text of the messages in question).
>>
>> Regarding one of Brian's comments, IIRC "addition" was simply what the BP
>> staff called the operation we're more used to thinking of as XOR. So that
>> might not be a source of error. They also spoke of dots and crosses rather
>> than 1 and 0. It’s just more natural for us today to XOR 1s and 0s than to
>> add dots and crosses. Brian is right about the shift codes, which helped to
>> create some of the regularities in the deltas exploited by the
>> codebreakers. IIRC, however, the shift codes get encrypted just like the
>> other characters, rather than being stripped out by the Lorenz equipment
>> prior to encryption as he suggests.
>>
>>
>> Brian’s code is just a NOT-XOR, which is just symmetrical. For the
>> operations, exchanging 1’s and 0’s is completely irrelevant, so using XOR
>> or its opposite doesn’t change anything.
>>
>> So I’m more and more convinced that the ciphertexts have been wrongly
>> given and copied from one website to the other… I’ve of course read the
>> "general report on Tunny" but unfortunately, the ciphertexts are not given
>> in it. So I guess I would have to dig through the archives… Any idea whom I
>> may contact?
>>
>> Regards
>> Emmanuel
>>
>>
>>
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Members <members-bounces at lists.sigcis.org> On Behalf Of Brian E
>> Carpenter
>> Sent: Sunday, May 23, 2021 6:52 PM
>> To: E. Lazard <Emmanuel.Lazard at dauphine.psl.eu>; members at sigcis.org
>> Subject: Re: [SIGCIS-Members] Question about the Tiltman break in Lorenz
>> cypher (1941)
>>
>> Emmanuel,
>>
>> On 24-May-21 09:47, E. Lazard wrote:
>> > Dear all,
>> >
>> > I’m looking for some original information on the famous "Tiltman break"
>> which led to the cryptanalysis of the Lorenz cipher en 1941.
>> > (https://en.wikipedia.org/wiki/Cryptanalysis_of_the_Lorenz_cipher
>> > <https://en.wikipedia.org/wiki/Cryptanalysis_of_the_Lorenz_cipher>)
>> > (http://www.eprg.org/computerphile/lorenz-combined.pdf
>> > <http://www.eprg.org/computerphile/lorenz-combined.pdf>)
>> >
>> > The story is: the British intercepted two messages sent with the same
>> key (HQIBPEXEZMUG) also called a "depth".
>> > When adding the two cipher texts with the exclusive-or function, the
>> key cancels out and what is left is the exclusive-or of the two plain texts.
>> > From there, brigadier John Tiltman found the two messages by trying
>> various likely pieces of plaintext and found that the first message started
>> with the word SPRUCHNUMMER (message number) and that the second message
>> also used the same word but shortened out as SPRUCHNR.
>> >
>> > EVERY SINGLE WEBSITE and the Copeland book "Colossus" list the two
>> intercepted cypher texts as:
>> >
>> > C1 = JSH5N ZYMFS 01151 VKU1Y U4NCE JEGPB
>> > C2 = JSH5N ZYZY5 GLFRG XO5SQ 5DA1J JHD5O
>> >
>> > and their exclusive-or as:
>> >
>> > D  = ///// //FOU GF14M AQSG5 SEKZR /YWHE
>>
>> Indeed,  S and 5 combine to give V according to
>> https://billtuttememorial.org.uk/codebreaking/teleprinter-code/
>> > My problem is that IT DOES NOT ADD UP!
>> > The U in 10th position is not the correct result, it should be a V.
>> > (S is 10100, 5 is 11011, so their exclusive-or is 01111 which is V)
>>
>> However, there are two problems with your comment:
>>
>> 1) The code for 5 is actually 11110, the same as the code for T, but in
>> figure shift. I assume that the Lorentz system removed the figure shift and
>> letter shift codes before starting the crypto work.
>> 11011 is indeed the figure shift code, so the actual bit stream would
>> have contained 11011 11110 11111.
>>
>> 2) The appropriate operation is not XOR. It's what Bletchley Park called
>> "addition", as described at the above web site. While that doesn't explain
>> this U/V error, which I suppose started as a transcription error, it
>> probably explains the other errors you mention.
>>
>> Regards
>>    Brian Carpenter
>>
>> > And I found other issues with all examples using the cypher text, the
>> messages, the key… I always have several letters which are wrong.
>> >
>> > So I’m wondering if I’ve misunderstood something or have the cypher
>> texts been incorrectly written down once and everybody just copied them
>> without checking?
>> >
>> > Anybody has genuine information or can point me to some source?
>> >
>> > Regards
>> > Emmanuel Lazard
>> >
>> >
>> >
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