Off the Grid

Off The Grid is invented by Steve Gibson (www.grc.com). Read all about it on https://www.grc.com/offthegrid.htm. The idea of this encryption is basically that:

• All hand-usable encryption methods, such as Ceasar's cipher, or Fairplay's cipher, have been cracked; the currently available computing power makes bruteforcing just too easy.
• However, how nice would it be to have an encryption algorithm that's easy enough to perform by hand, but still impossible to crack by computers? Such a method could be safely performed without any electronic means - "off the grid" - but would still be safe.

How does OTG work?

OTG encrypts a-z

Latin Squares

a b c d e f g
b c d e f g a
c d e f g a b
d e f g a b c
e f g a b c d
f g a b c d e
g a b c d e f

b D C e A G f 
F a b g c d E 
A e D B G F C 
D F G c E b a 
C g a F d E B 
G B e a f c d 
E c F D B A g

What's the algorithm, what's the key?

So what's the algorithm? For every character a-z in the input, OTG will output 2 characters. Here's how. First a description, then an example to illustrate:

1. In order to encrypt a character, start scanning from the scan coordinate, which is initially (0,0).
2. Take turns scanning horizontally and vertically. We'll start horizontally. So the first character must be scanned for in the top most row.
3. Given the fact that we're working with Latin squares, we are always sure to find the character that we want to encrypt. There's no need to switch to a different row or column.
4. When scanning horizontally:
   • If the character to encrypt is to the right of the scan position, then output the 2 characters following the input character. Move the scan position just beyond (to the right of) the output characters.
   • If the character to encrypt is to the left of the scan position, then output the 2 characters preceding the input character, but in reverse order (reading right-to-left). Move the scan position to just before (to the left of) the output characters.
   • If the character to encrypt is at the scan position, then act as if it were to the right; i.e.; output the two characters following the input character, and move the scan position to the right of the output characters.
   • When outputting the characters, or moving the scan position, we may need to "wrap around" the row.
   When scanning vertically:
   • If the character to encrypt is below the scan position, then output the 2 characters below the input character. Move the scan position just below the output characters.
   • If the character to encrypt is above the scan position, then output the 2 characters above the input character, but in reverse order (reading bottom-to-top). Move the scan position just above the output characters.
   • If the character to encrypt is at the scan position, then act as if it were below; i.e., output the two characters below the input character, and move the scan position below the output characters.
   • When outputting the characters, or moving the scan position, we may need to "wrap around" the column.

An Example

Encrypting: "h", horizontally. 1. Start at (0,0), the "S". 2. Find "h" horizontally. 3. Output the next 2 characters, "CG". 4. Move scan position to the "W". So far nothing out of the ordinary.
Encrypting: "e", vertically. 1. Start at (24,0), the "W". 2. Find "e" vertically. 3. Output the next 2 characters, "Fj". 4. Move scan position to the "v". So far nothing out of the ordinary.
Encrypting: "l", horizontally. 1. Start at (24,18), the "v". 2. Find "l" horizontally. 3. Output the next 2 characters, "SE". 4. Move scan position to the "G". Note that we had to scan left. The output is therefore "SE" (right to left).
Encrypting: "l", vertically. 1. Start at (4,18), the "G". 2. Find "l" vertically. 3. Output the next 2 characters, "Os". 4. Move scan position to the "k". Note that we had to scan up. Then we found the "l" at the topmost row, so we had to "wrap around" to the bottom.
Encrypting: "o", horizontally. 1. Start at (4,23), the "k". 2. Find "o" horizontally. 3. Output the next 2 characters, "Nq". 4. Move scan position to the "d". Note that we had to scan right. Then we found the "o" at the rightmost column, so we had to "wrap around" to the leftmost position.

Why are there lower and upper case characters in the square?

For the purpose of this challenge the upper case characters don't really matter (in fact, they might make the solving challenge even easier).

Can OTG decrypt?

Do you have something to play around with?

• Generate Latin squares,
• Encrypt strings on the command line or files,
• Decrypt,
• It accepts arbitrary alphabets (but defaults to a-z).

• Download the script, and save it to a file, say /usr/local/bin/otg.
• Make the file executable using

  chmod +x /usr/local/bin/otg

• Generate your Latin square (your encryption key), using:

  otg -g print > MySecretSquare.txt

• Try to encrypt, say you have a file plain.txt:

  otg -l MySecretSquare.txt encryptfile plain.txt > encrypted.txt

• Try to decrypt:

  otg -l MySecretSquare.txt decryptfile encrypted.txt

This is OTG V1.02 - Off The Grid encryption/decryption made easy!
Read https://www.grc.com/offthegrid.htm for more info.
Copyright (c) Karel Kubat, karel@kubat.nl, http://www.kubat.nl.

Usage:
  otg -g [-a ALPHABET] [-n SWAPS]          print
  otg -l FILE [-a ALPHABET]                print
  otg -l FILE [-a ALPHABET] [-s SEED] [-v] encryptfile FILE
  otg -l FILE [-a ALPHABET] [-s SEED] [-v] encryptstring STRING
    Flag -a: Default ALPHABET is abcdefghijklmnopqrstuvwxyz
    Flag -g: A new grid is generated.
    Flag -l: A grid is loaded from the FILE (use - for stdin)
    Flag -n: Default SWAPS is 100. More is more random.
    Flag -s: Seeds encryption/decryption. Default is to start at (0,0).
    Flag -v: Makes encryption more verbose

Typical usage:
  otg -g print > MySecretGrid.txt
  otg -l MySecretGrid.txt encryptfile Plain.txt > Encrypted.txt
  otg -l MySecretGrid.txt decryptfile Encrypted.txt

The Challenge

yI oB IS EU ab Hj ZG ZD Vp jc wb bz rk eD Tc uN pW qp IK rX ev wT vU gy hv jc 
wb bz xF OD Yl Md XM xg Ks oE kf wX tV sr xF jA yr mX PG Wb gK jT iA RQ Je cx 
jD Ic aH tP tf Go EO pT FE nF Aw RG yg Jr Tl JO ad pH ZK Dc eY Gz Ur gh Is rB 
TN Uy bK md jZ Am tQ Wm yN Rt DC oQ cP sC Tz fz vf ph Bw Eh OX cT Yl vR ha yg 
WE dS ad de an by ta eD Yt Ic Qp wn Uq tb PJ Zg fL lT Aw Md zM hP il Zd yo Mt 
lk bN BJ mO rQ xg fb AV sI Jd rN Ry Bt fa Aw RG nv Xt Ix DY Nq Xg hM de zt JT 
ks Rq XM Kd TJ WL Xm dB JU Gz Hv Qv hs Qb Cg yl ps nf vp Su eK iM rd fQ KA ea 
GQ Ic aH tP eK Aj CR CI nM Ch wb Vf pW Ar fH WL qp oB tj mX bT Vf rt jt dg Bz 
th QH nc rY SU dS bf Wb bX kJ Fx sG LU sr Et Rt as QV zN dX vf LQ vH tO fD bk 
Rt NM gk De Kj qJ CQ JX tR WU Tp Nm gK jT tV xU fD Hj ca rX vG mO kT EH nS wt 
sK wd gt Mi kI lq Dx hs tE jR vy Er lO Ct ox Fh zN Tv lk hp TN Uy Li dU sk Eq 
xm gU LU Vh qz YD NF us nS ZJ tj Ux de Cw lQ hp Xc pe zS YK Rq Ji Uv sZ sV ch 
Sl Is aL li hv oN oX Im xF pH JN cT rt Nb rz DW QR ic rz HS xM yu re Jd Sl jR 
yI Oe CZ pL BQ sd Nv IK tf SL Ng Ry Bt Eh vU gy BT jR yI Qb WO HY SO JO bK md 
md kS MT Cw UD zU PA SL Ru lT cO Qe FB Ot IF oQ nc qw nM UM pQ oB sM Sd iM JT 
Hp Ng Qt ap bo DZ oX vj eR Ux kg AV WE Bj Zj HG dN UM as Qw ad eI PJ Wy zU jP 
xM Rq gk zL Qt Cb nc Kw rt Ch hz jB Ro qr FH Hl xZ nZ WO IK nO jB Qe su sl HI 
LM qf mD oN DP Ep xQ Ps PQ Ia zs yl ps Sd cn Rt CD oa zN qP BY VF EY Jk Wl cx 
LM IL bT Ji TU zD pR wT lk oQ Jr xg Ks YF Lf mq Sh CA mc dC AE hp NX Tl Wl Fp 
ER UE Vq vk iM Ax ks tv WE dS Mh tM XU sC YF UM CI oz Oh Lv Wr aW sa SY WM OC 
Cg bw ws Qv Je gs RJ EA uD Bj Zj bH LI ng XY Cs hk wT Qp MU Ri zP rk ea Qu vT 
fD eD PG cY iK SP ih TC hu nZ BO Fz LS KS WI BZ ab Oa Yl bz lS sd pQ oB ML DE 
ji fk gk mt DB Cb OX cT dr iM lY Zk Tr pz Qy Vh Se jD xm QM kr BY VK rX vG Fi 
Oa Nb ok KS WI BZ ab Oa hs Qb WO qR WM TF BD wd nM hs tE Rv Xd ZJ Rt Px ZC hp 
Xc HF PG Ej Wl aM md ZI BT bz zv zp yS oJ ok DL sz Jd kI RT tE Kd of Ft zU Bl 
Mp XN RJ yg vp Zl cu Zf bK md Gy pH lY dJ JN jw CD Kd fY Eq yO pH rt WL zU sd 
pQ cN Iw Gk DC hs Ch mN IY jT tV xU fD Hj ca rX vG mO fJ nd gF tw EF GN yo Nl 
Lr pX hz QL SL tv md cT hs eQ wJ HQ La FL rM Ic lk ao xN ng oX Bo BO Fz QV Vf 
JN DG BT bz zv DL sz Cw sE qs bs JX tR ae za hg OX MO yN gh dn UZ vy Er OD gh 
bK Nm yS ZO rz iM sh BV yH gZ Hy hp Es bx it Uy nM xg Ks tv WE dS Mh jA Uq tb 
iA VQ Vp CT zP HF KI VJ MH Ck hv xE hC ks yw Os wQ LX Wp RS Sh FO Lp by Je cx 
xm wP Wv Ps Hg Jd GE rA FB bW aW Nb aW mI Lb zS cd rB BO nD Hy XD lc pa Mh SF 
FB Uy Li aC fq Nm aU xb Hn YD at vh sg zF ad sG vp WL qp UW bo xM Tk eB sg fa 
dx sL ZU Zd CE tb Hp hs Ch kJ Gu hp Es Uq wb jR TM WQ BH zP OJ vI sM Sd iM JT 
Hp dJ lY Zk zT nW WE dS GP DL mX Mt Od ZU zO rX Mh CH Ex YH dk MX XV vU zP yZ 
EI JO ad de YX Xg bK aR CE Nl dn gU Qh GU gK ba ps XL xF xK KY km UT DY qP LK 
qJ Rq CQ JX tR tC Aw RG vf EU wb Vf al nr pW mA fu kv ad de YX vr jc Dj Od pj 
Vp ZU zO rX hi Cw UD qt RW mu AR xy tj Ux PF rX Mh tb Yl if Td bx Bk Tl hs eQ 
Rp Xd RJ yg Gy mu zO dS Mh tb Yl if Td DU aL Wb pO pz IS Ji yH xU vm VQ sk Uv 
wb Vf JN cT rt WL qp Ps Hg Jd GE rA FB bW ks mt KL bP BQ Oe fu ax qJ vt Cg eV 
BQ Wa Iy mt EK us Ro qr PJ Jd Gu DX zG xg pT Ry LB Oj KL bP Es Wm Xp Rp Od dC 
tV xU Tg DW xj tB PF aE bX Ic nv Wu Xr fk xM fZ dW ax RW rY dW Fu OX Fv RJ ry 
Oi jb gt HC Wl cx GL dC FH Hl xZ ZJ Vc Oa dr Aj CR vL kg zc FM DU Vz iM bX Ic 
nv RQ at LX sh tX DC Jd xF tb IY xP hv CO YF Kd QB zB Wp RS jQ AV av Pz bX dH 
tj hE Ge Kc bo QM Mb Sz Od jp yw QV zN lT CN Xp Vq by Xm hX id kJ yS rX sY RT 
tE Fh az XW sd zU bT bP BQ ZC hV tv WI rY CE zK Ai gh GA nA DU bw PJ dJ lY oQ 
bs kC tf SL vf Ux YF hC rd tM JB kJ zh Ic Qp tM JB GX rz rx Mq Dy tZ ig tf LX 
al mZ lz EQ eK iM sh HW kI oj dV wX ub Rt Lf Dc gd aW CD Nb di VA tj Jd Sl dU 
BO Fz Fh Rq fJ IJ DA Jr gk Pa Kn sd sl HI nH Qv gK jT ZD hj PQ aC sY oj Kj pe 
SX Wx QG uc Se Mu Sc Jr Tl sk zr pH hs Oe CZ uy vG mO fJ QT Td DU aL Wb FN gy 
PE rY yo Gz bT Vf rt Ch hz Om IY xP jQ zc SO xB Qp ry tW su yH Ji yH hs EW JH 
bo xM Tk eB CD xE tN wd EF Fu rb gU pR CT Mg Gu lO DY Fx JX tR br kt HW dx aC 
vG SR jg eD cJ UK ER tf Wx wd tQ cd FN nL kZ IN zG oN oX jc hU li Xs Bl WO Qv 
ta DZ DP gy Cg eV BQ Wa jc tb iA pf Wl tb PJ Ux YF Mo pO pz kt QV Ua Bt ZR QF 
xm xM BE Bl Uz ba ps fk qS cG ER hp sk sP kZ WL ja YH BG Sk AR QL SL lZ GA nA 
UJ rY CE Gz oX eV aB AV zG dw GL pa hi rX vG hj md qw ev pj Jf iJ vG mO yw md 
dh GU eg uM xm gU vp WL iK Bj qb um Rl IL bT Ji Wm pj Xc HF PG Mi dx xg Ks lH 
tQ Bj fC QF xm xM UI qJ dh HK Vp MN YF IN fH ER Je Vy Hw XL lF QM Ik lT xF jA 
yr IS hQ Fz Nz eV BQ Wa Nk nr JN kL nu oQ cP Os Ex QT Jf sr lF FT lJ Ic vU sO 
gK oE Is hp TN Uy ih gU Yt Ic Qp BE DN cj BH Om IY xP jQ Vk BY OJ CE xr ij ft 
PG Nl dn IK Od ap bo ZU md UA MJ jA vh LY PN li Bw XM Lf Uk FS dS pT WB gk bw 
VK nf ba NM Yt Uq ja QT YI mt rz jA yr hE Li sL lv Ck PQ yQ Cn Oa Rp rX sY RT 
tE oa Bw wd ZG ab rU md WI YH MW rX hM YH RJ pX IA Fp WM TF BD wd jU QT Td Uq 
hU li lO Ct GZ tO Cg JH bo xM CQ IJ be DY qP Gm Ix kg wX Zg vy rX Mh FQ YX rw 
TB fi ps XL bM QT XN QN ja nr ZK Fz LS vR UG dJ lY oQ br qB WO Zl uN sy ku Xw 
Yt DU WO IK hS tb PJ PR RJ kj kI RT WI Gk vy rX hi Cw UD Bq yF VJ MH dn Tk Xg 
hi Cw UD Bq bk nc yv FK WI YH ER LS WL UN CQ IJ DA sr kI pz Ko jA yr or Ix DY 
Nq Wn Wr Oa gk ab KI eV aB Xp ta ZU RB jp fJ IJ FC xW Ng cI QC dn kg LK RW rY 
mj LY iA pf Wl et LF wT Qp AV av zP qN sq dL Ic vU JO hM Xw mB PK vW LK La dn 
BE Bl KL hE pR QN wb UM pQ wq Zx MK JB yZ Vp dM zO Xr kf dn za Jf YF vK cm Wm 
zG Ch rk vL eY Mt as Se bs CH Ex YH dk by FN Ru hU jA zl WB Fi cU zN Ae gk VJ 
MW rX vG hj jc Dj Od QN KY pT BF oI Vc LH md UA Qt sg ps Er OD qm xm eV Es Wm 
La YH RJ lB Xm Rq QC Mi xF Mt CI XD Ai Ft dn QM EG gX KA ea Hp QL rz Mi SJ jk 
tE Rq gk Qv Je gs RJ AV HP wd vj VJ dk ZJ KY pT gs PR RJ lB Xm Rq QC Wb iY DZ 
Qt HQ dm Qf GZ LY wm kU IS Jd Sl dU aZ Vk LB UN ps Jo JY wT UT DY qP cX CE EG 
qp sn TJ Nb di pX th uS zO dS be ac bT dJ pW Ic Nv DY EG RQ Je cx Ih pj ER fa 
Aw CS lz Rh de rX ev uS md jc hU li Xs sp cT Ax MW Er QC Mi Aw Md Iy WL Rt oN 
DP OJ IC Jd th NQ nv HW rk jP Yt Ic Qp tM JB WT hu MB yF VJ GQ Ic nv HW rk vL 
bz WB Fi gN lR bW RJ pX zv tO yn Mi th QH kt QV Dh cx Xo wn fD CI Mn Jd Sl oa 
Ua Bt cd kc bL xB fH Ps dN WE dO Bj Xo wn BT bz dx sL ZU Zd yH gZ gt Aj CR vL 
kg zc xt pj sE HW rk br dr Zd Nv wX cu xM Tk ZH OV ks yw Os wQ Er QC il rz FQ 
SL lZ yv AW ps fk gk mt KL gN GL pa sY sg za ac UN rB NX Ar wQ Bq Qx zp jg Wr 
IF EU ab bk Lp by ta Ug wl ig Zj zS RW pH dr iM lY bN Yt Ft dn QM ht rq qI jp 
kT GU eg uM fr kn WI YH ER fa kI jy aB sp nM jR xw Md Nz vb AP Ma pQ ZI gC Go 
sI Ux de rX GP DL mX cU yv Hy Fm ZO rz Mt kf Bv HB mo Fi Qy Qx zp tZ mN PJ Ux 
YF oa lO eD dn gU BJ cG ER mX JY zG CQ IJ YJ Eb QC lN br qB BT bz SJ Bl nD Rt 
CD Py CQ jE aO EU hu Rt uE FV wl RQ dr Mi vy UK fZ Bq yF VJ ks Px wb bP Nx wX 
cu xM Nz vb AP Ma pQ ZI af sO Op qf Rp UK fZ SL Bw kv GA Ax aW Nb aW cj KL Vf 
eJ Tl pW eI gK oE vy jb uN sy ku Yr dn CO bz mN dk vk WO Dz md UA OX cT al ed 
qf SR xm gU cn DY qP SA iM Ax Yl gZ tQ vI Ku qt Bm HW kI pz li YF Iy UM sl oE 
mv xB as zS up Dz PQ UM Nv Ow ks yl ps rX XU Nm cJ Ic Qp tM hQ jy wZ Vb YE Uy 
Mh tb Zf ph Bw Gu lO DY Aw jR dm Uy Kz vy nc Qv al dn za BM Tg Gz NU ch kI RT 
tE Nb di zc JB yZ wZ Ic Qp AV na rX eG GU KZ sy Tk VF gk 

Conditions

• The essense of the challenge is as follows. Me and a counterparty have in our possession the same Latin square. We're exchanging messages and chatting about highly secret stuff. You are tapping our conversation - listening on the wire - and you see only the encrypted text flowing by.
• Crack the above encrypted text.
  • You may assume that it's natural language text (though only a-z are encrypted, spaces and punctuation marks are skipped).
  • Furthermore you may assume that the encryption started at (0,0), just as the example that I have given above.
  • The encrypted message is a result of one (long) text, it's not a simple short sentence repeated ad lib.
  • Also rest assured that the encryption square is different than the example above ;-)
• Send me the solution by e-mail to karel@kubat.nl.
• The first one to send me the solution gets the prize. As simple as that.
• With your solution, send me a description how you did it, and preferably the code that solved it (I'm assuming that you'll need a computer for the cracking.)
• I'm the sole judge of the validity or invalidity of your submission. For example, if you only guess the outcome without a complete decryption process, then your submission won't be considered.
• The winner gets full credits, on this page, plus a set of Zen magnets (see video below).
• I'm pretty sure that Steve Gibson will be very interested if you crack it. Should be interesting!
• Oh by the way. I haven't started cracking this thing yet. I can't comment (yet) on the (im)possibility of the endeavor. I will give it a try though as soon as I find the time. However, also feel free to send me your deliberations, most interesting comments will be included on this page.
• Good hunting!

My own attempts