'Copyright 2000 The American Cryptogram Association (ACA)
'3613 Piedmont Drive, Plano TX 75075-6234
'All rights reserved.

'Program code from the Computer Column
'for Nov/Dec 2000.  The program drags
'a crib through three-square ciphertext
'and displays the number of matches at
'each cipher position.  See the Computer
'Column for details.

'Sq3Crib.Bas    Demo ciphertext is from
'E-21 Jul/Aug 2000

C$=   "ENT VUB VET BLA BTB BEU MIA KPY"
C$=C$+"LPE ONH ASY MQG ANN AHT OZY BYA"
C$=C$+"DWC MXC ENB MPE KNH LII VKN HLP"
C$=C$+"NMG CMF ISL KRP PML SKU RKM ZVM"
C$=C$+"FWT QMR YNX LQO ASS GKB XKS XME"
C$=C$+"WVV TMZ NLY UWH VUN MUC CKA BNI"
C$=C$+"OID PVF IUU FKL DOR RVO GIG HTV"
C$=C$+"ERT ZMR TKY BKX LPE USC XKF MWB"
C$=C$+"KMI QMM VXL CYR FKX YSH HDN NYK  
C$=C$+"IKE SSO PLF RLU XMS ZLZ BSA WRT"
C$=C$+"AMG LLL ENR NMV OCY CWQ DRX KNX" 
C$=C$+"GVC CWI PYD TCS UVR EBX"

'Crib is next
Pt$="MAYBEONEOFMANYTHINGSITCANMEAN"

Ct3$ = RemoveSpaces$(C$)
Ct2$ = RemoveMiddleLtr$(Ct3$)
LPt  = Len(PT$)
LCt2 = Len(Ct2$)
NumPtPosns = LCt2 - LPt + 1

'Ct2$ is cipher with middle letters
'omitted. Pt$ is dragged from posn
'1 to NumPtPosns in Ct2$,  CLin$
'receives triads to be printed. NLin$
'holds the counts to be printed. 10,
'11, 12 are shown as a, b, c, etc.

CLin$="" : NLin$="" : TriadCount=0
For I = 1 to NumPtPosns Step 2
  Triad$ = Mid$(Ct3$,2*I-(I+1)\2,3)
  CLin$  = CLin$+Triad$+" "
  CtSeg$ = Mid$(Ct2$,I,LPt)
  N1$    = Coincidences$(CtSeg$,Pt$)
  CtSeg$ = Mid$(Ct2$,I+1,LPt)
  N2$    = Coincidences$(CtSeg$,Pt$)
  NLin$  = NLin$+N1$+" "+N2$+" "
  TriadCount    = TriadCount+1
  If TriadCount >= 18 Then
     Print CLin$ : Print NLin$
     CLin$= ""   : NLin$=""
     TriadCount =  0
  End If
Next I
  If Clin$<>"" Then 
     Print CLin$ : Print NLin$
  End If
End ' End of main program

'Returns count as char: 0-9, a=10 etc.
Function Coincidences$(C$,P$)
C=0            'C is count of matches
L = Len(P$)
For I=1 to L
  If Mid$(C$,I,1) = Mid$(P$,I,1) Then
     C = C + 1
  End If
Next I
If C<10 then A=48 else A=97 : C=C-10
Coincidences$ = Chr$(A + C)
End Function 'Coincidences$

Function RemoveMiddleLtr$(S$)
  T$=""
  L = Len(S$)
  For I=1 to L
    If ((I+1) Mod 3)<>0 Then
       C$=Mid$(S$,I,1)
       T$=T$+C$
    End If
  Next I
  RemoveMiddleLtr$=T$
End Function 'RemoveMiddleLtr

Function RemoveSpaces$(S$)
  T$=""
  L = Len(S$)
  For I=1 to L
    C$=Mid$(S$,I,1)
    If C$<>" " Then T$=T$+C$
  Next I
  RemoveSpaces$=T$
End Function 'RemSpaces