[GreenKeys] NSA 5-level tape on poster

[Christian Gauger-Cosgrove]

On 19 June 2018 at 16:15, Nick England <navy.radio at gmail.com> wrote:
> I came across this NSA poster showing 5-level tape, evidently with a 6th
> punch to show rubbed-out characters. Was this a common feature or
something
> special for the crypto world?
> http://www.navy-radio.com/tty/reperf/nsa-security-tape.pdf
>
I can't speak for that specific application of a sixth punch. But I am
aware of a security related use for tape with a sixth punch. The British
(and thus used by the entire Commonwealth) BID/08/05 through BID/08/08
"ROCKEX" and BID/590 "NOREEN" one-time-tape machines used a six-level key
tape punched mostly with standard 5-level code, with the sixth bit used to
signal "output these characters directly in the ciphertext/skip these in
the plaintext".

That's because both machines were built in such a way that instead of a
"pure" one-time-tape cipher it does some extra work to make sure that the
ciphertext is only alphabetical characters, and it also blocks the
ciphertext into 5-letter groups, in blocks of 50 groups.

So, for instance the output looks like:

AAAAA ZQVAI HVCDJ BDSAZ MBFYP  QXBAL GPMLN VWTQH SOOES PXQRW
UNFOA BXSMW ODEMT TSXMO HWVSS  OVVNM RZMXG UVWZS WPCUJ YCCYU
SBQUD UPVDE RGMBX YXBVS XNXDI  JYZKK CKWVJ OPEEX OWTHK DMPAA
KFWVW BLMYO FVKWK LWTKW WPDSS  PAEYW YSMIB NCKCE YGGTR ICTQM
ERWER XHUPG DQWWY ESZRT XGKWK  JPZRZ QHEFQ MXKJG CUJQN WHKOJ

AAAAB DZCDR TLGVY AAXCZ VYUHL  HSVFK FSEKS KPHTJ JXTXE KVNNW
FFWPM QUWYN SRVHF HSHBL CICPN  OUSDU WNTTJ UKWKC POWCP QRJQL
KBKEL VQFQC XRUEQ XONVP RFSRL  FWWFG ALNQH YHWTT IYFTE YULUV
NTJQX RSAYT UMJCL XUVUP UNCYF  LILJQ UFETV KQDOL PCVIO KEFGJ
FXUGQ EUXIK UJFPZ VGKDZ MQEWH  RDILW GVIKX TNPRH IFYYS DQSSI

The first group is an indicator so the person at the other end knows to
start their key tape at the right point. The indicator group, spaces and
new lines are all indicated in the key tape and thus are not decoded when
you get the plaintext.

The "neat" thing is that while the output looks like the output of a
TSEC/KL-7, it's actually enciphering standard teletype 5-level code, so the
plaintext can be formated however you wish (though there might be long runs
of NUL characters where the machine had to skip the next key letter to
avoid the enciphered character not being in the A-Z range).

There's a bunch more info on the Crypto Museum webside, and on Jerry Proc's
pages on both the ROCKEX and NOREEN.

Crypto Museum:
ROCKEX <http://www.cryptomuseum.com/crypto/uk/rockex/>
NOREEN <http://www.cryptomuseum.com/crypto/uk/noreen/index.htm>
Jerry Proc:
ROCKEX <http://www.jproc.ca/crypto/rockex.html>
NOREEN <http://www.jproc.ca/crypto/bid590.html>

Jerry Proc's pages discuss the use of ROCKEX/NOREEN in their application of
enciphering the communications of Global Affairs Canada (which was Foreign
Affairs Canada up until 2015, and External Affairs Canada up until 1995).

- Christian
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