// (1) Copy text into tmp buffer and remove non-alpha chars.

Chdir(PATH_ONLY)
BOF
Reg_Copy(10, ALL)                       // copy text to new buffer
Buf_Switch(Buf_Free)
Reg_Ins(10)
BOF
Replace ("|!|A", "", BEGIN+ALL+NOERR)   // remove non-alpha chars
Reg_Copy_Block(10,0,EOB_pos)            // @10 = text to be analysed

#20 = Buf_Num                           // buffer for text being analyzed
#21 = Buf_Free                          // buffer for English frequency list (A-Z)
Buf_Switch(#21)
Ins_Text("8167 1492 2782 4253 12702 2228 2015 6094 6966 153 772 4025 2406 6749 7507 1929 95 5987 6327 9056 2758 978 2360 150 1974 74")
File_Open("unixdict.txt")               // or use "|(MACRO_DIR)\scribe\english.vdf"
#23 = Buf_Num                           // buffer for dictionary
#24 = Buf_Free                          // buffer for key canditates

Buf_Switch(#24)
for (#1=0; #1<5; #1++) {                // Fill table for 5 keys of 50 chars
    Ins_Char('.', COUNT, 50)
    Ins_Newline
}
#22 = Buf_Free                          // buffer for results

#25 = Reg_Size(10)                      // number of letters in the text
#26 = 26                                // number of characters in the alphabet
#61 = min(#25/10, 50)                   // max key length to try

// (2) Check Index of coincidence (or Kp) for each key length

Buf_Switch(#22)                         // buffer for results
Ins_Text("KeyLen Kp   dist ") Ins_Newline
Ins_Text("-----------------") Ins_Newline
#13 = Cur_Pos
#7 = 0                                  // no Caesar encryption
for (#5=1; #5<=#61; #5++) {
    Buf_Switch(#20)                     // text being analyzed
    BOF
    #54 = 0;                            // sum of Kp's
    for (#6=0; #6<#5; #6++) {           // for each slide
        Goto_Pos(#6)
        Call("CHARACTER_FREQUENCIES")
        Call("INDEX_OF_COINCIDENCE")    // #51 = Kp * 10000
        #54 += #51
    }
    #54 /= #5                           // average of Kp's
    Buf_Switch(#22)
    Num_Ins(#5, COUNT, 3)               // write key length
    IT(": ")
    Num_Ins(#54, NOCR)                  // average Kp
    Num_Ins(670-#54)                    // distance to English Kp
}
Buf_Switch(#22)
Sort_Merge("5,12", #13, Cur_Pos, REVERSE)  // sort the results by Kp value
Ins_Newline

// (3) Check the best 4 key lengths to find which one gives the best decrypt result

#38 = 0                                 // max number of correct characters found
#19 = 1                                 // best key length
for (#14 = 0; #14<4; #14++) {           // try 4 best key lengths
    Buf_Switch(#22)                     // results buffer
    Goto_Pos(#13) Line(#14)
    #5 = Num_Eval(SUPPRESS)             // #5 = key length
    Call("FIND_KEYS")                   // find Caesar key for each key character
    #4 = -1                             // try best match key chars only
    Call("BUILD_KEY")
    EOF
    Ins_Text("Key length ")
    Num_Ins(#5, LEFT)
    Reg_Ins(10)                         // encrypted text
    BOL
    Call("DECRYPT_LINE")
    BOL
    Call("FIND_ENGLISH_WORDS")          // #37 = number of English chars
    EOL Ins_Newline
    Ins_Text("Correct chars: ")
    Num_Ins(#37)
    if (#37 > #38) {
        #38 = #37
        #19 = #5
    }
    Update()
}

Ins_Text("Using key length: ") Num_Ins(#19) Ins_Newline
#5 = #19
Call("FIND_KEYS")                       // find Caesar key for each key character

// (4) Decrypt with different key combinations and try to find English words.
//     Try key combinations where max one char is taken from 2nd best Caesar key.

#38 = 0                                 // max number of chars in English words found
#39 = -1                                // best key number found
for (#4 = -1; #4 < #19; #4++)
{
    Call("BUILD_KEY")
    Buf_Switch(#22)                     // results
    Reg_Ins(10)                         // encrypted text
    BOL
    Call("DECRYPT_LINE")
    BOL
    Update()
    Call("FIND_ENGLISH_WORDS")          // #37 := number of correct letters in text
    if (#37 > #38) {
        #38 = #37                       // new highest number of correct chars
        #39 = #4                        // new best key
    }

    EOL IT(" -- ")                      // display results
    Num_Ins(#4, COUNT, 3)               // key number
    Ins_Text(": ")
    for (#6=0; #6<#19; #6++) {          // display key
        #9 = 130 + #6
        Ins_Char(#@9)
    }
    Ins_Text("  correct chars =")
    Num_Ins(#37)
}
Ins_Text("Best key = ")
Num_Ins(#39, LEFT)
#4 = #39
Ins_Newline

// Display results
//
Buf_Switch(#24)                         // table for key canditates
BOF
Reg_Copy_Block(14, Cur_Pos, Cur_Pos+#19)  // best Caesar key chars
Line(1)
Reg_Copy_Block(15, Cur_Pos, Cur_Pos+#19)  // 2nd best Caesar key chars
Call("BUILD_KEY")
Buf_Switch(#22)
Ins_Text("Key 1: ") Reg_Ins(14) Ins_Newline
Ins_Text("Key 2: ") Reg_Ins(15) Ins_Newline
Ins_Text("Key:   ")
for (#6=0; #6 < #19; #6++) {
    #9 = #6+130
    Ins_Char(#@9)
}
Ins_Newline
Ins_Newline

// decrypt the text with selected key
Ins_Text("Decrypted text:") Ins_Newline
Reg_Ins(10)
BOL
Call("DECRYPT_LINE")
BOL Reg_Copy(13,1)
EOL Ins_Newline

// Find English words from the text
Reg_Ins(13)
Call("FIND_ENGLISH_WORDS")
EOL
Ins_Newline
Num_Ins(#37, NOCR) IT(" of ")
Num_Ins(#25, NOCR) IT(" characters are English words. ")
Ins_Newline

Buf_Switch(#20) Buf_Quit(OK)
Buf_Switch(#21) Buf_Quit(OK)
Buf_Switch(#23) Buf_Quit(OK)
Buf_Switch(#24) Buf_Quit(OK)

Statline_Message("Done!")
Return

/////////////////////////////////////////////////////////////////////////////
//
// Caesar decrypt current line and count character frequencies.
//   in: #5 = step size, #7 = encryption key, #26 = num of chars in alphabet
//  out: #65...#90 = frequencies, #60 = number of chars

:CHARACTER_FREQUENCIES:
    Save_Pos
    for (#8 = 'A'; #8<='Z'; #8++) {
        #@8 = 0                         // reset frequency counters
    }
    #60 = 0                             // total number of chars
    while (!At_EOL) {
        if (Cur_Char >= 'A' && Cur_Char <= 'Z') {
            #8 = (Cur_Char-'A'+#26-#7) % #26 + 'A'  // decrypted char
            #@8++
            #60++
        }
        Char(#5)
    }
    Restore_Pos
Return

// Calculate Index of Coincidence (Kp).
//   in: character frequencies in #65...#90, #60 = num of chars
//  out: #51 = IC * 10000
//
:INDEX_OF_COINCIDENCE:
    Num_Push(10,15)
    #10 = 0
    for (#11 = 'A'; #11<='Z'; #11++) {
        #10 += (#@11 * (#@11-1))        // Calculate sigma{ni * (ni-1)}
    }
    #12 = #60 * (#60-1)                 // #12 = N * (N-1)
    #51 = #10 * 10000 / #12             // #51 = Kp * 10000
    Num_Pop(10,15)
Return

// Find best and 2nd best Caesar key for each character position of Vigenère key.
//   in: #5=step size (key length)
//  out: keys in buffer #24
//
:FIND_KEYS:
    for (#6 = 0; #6 < #5; #6++) {               // for each char position in the key
        #30 = -1                                // best key char found so far
        #31 = -1                                // 2nd best key char
        #32 = MAXNUM                            // smallest error found so far
        #33 = MAXNUM                            // 2nd smallest error found so far
        for (#7 = 0; #7 < #26; #7++) {          // for each possible key value
            #35 = 0                             // total frequency error compared to English
            Buf_Switch(#20)                     // text being analyzed
            Goto_Pos(#6)
            Call("CHARACTER_FREQUENCIES")
            Buf_Switch(#21)                     // English frequency table
            BOF
            for (#8 = 'A'; #8<='Z'; #8++) {     // calculate total frequency error
                #34 = Num_Eval(SUPPRESS+ADVANCE)
                #35 += abs((#@8*100000+50000)/#60-#34)
            }

            if (#35 < #32) {                    // found better match?
                #33 = #32
                #32 = #35
                #31 = #30
                #30 = #7
            } else {
                if (#35 < #33) {                // 2nd best match?
                    #33 = #35
                    #31 = #7
                }
            }
        }
        Buf_Switch(#24)                         // table for key canditates
        BOF
        Goto_Col(#6+1)
        Ins_Char(#30+'A', OVERWRITE)            // save the best match
        Line(1)
        Goto_Col(#6+1)
        Ins_Char(#31+'A', OVERWRITE)            // save 2nd best match
    }
    Buf_Switch(#22)                             // results buffer
Return

// Combine actual key from 1st and 2nd best Caesar key characters
// Use 1st key chars and (possibly) one character from 2nd key.
//  #4 = index of the char to be picked from 2nd key, -1 = none.
//  #5 = key length
//
:BUILD_KEY:
    Buf_Switch(#24)                     // table for key canditates
    BOF
    for (#6=0; #6<#5; #6++) {           // copy 1st key
        #8 = 130 + #6
        #@8 = Cur_Char
        Char(1)
    }
    if (#4 >= 0) {
        #8 = 130 + #4                   // pick one char from 2st key
        Line(1)
        Goto_Col(#4+1)
        #@8 = Cur_Char
    }
    Buf_Switch(#22)                     // results buffer
Return

// Decrypt text on current line
//   in: #5 = key length, #130...#189 = key
//
:DECRYPT_LINE:
    Num_Push(6,9)
    #6 = 0
    While (!At_EOL) {
       #9 = #6+130
       #7 = #@9
       #8 = (Cur_Char - #7 + #26) % #26 + 'A'   // decrypted char
       Ins_Char(#8, OVERWRITE)
       #6++
       if (#6 >= #5) {
           #6 = 0
       }
    }
    Num_Pop(6,9)
Return

// Find English words from text on current line
//  out: #37 = number of chars matched
//
:FIND_ENGLISH_WORDS:
    Buf_Switch(#23)                     // dictionary
    BOF
    While (!At_EOF) {
        Reg_Copy_Block(12, Cur_Pos, EOL_Pos)
        if (Reg_Size(12) > 2) {
            Buf_Switch(#22)             // buffer for results
            BOL
            while (Search_Block(@12, Cur_Pos, EOL_Pos, NOERR)) {
                Reg_Ins(12, OVERWRITE)
            }
            Buf_Switch(#23)
        }
        Line(1, ERRBREAK)
    }

    Buf_Switch(#22)
    BOL
    #37 = Search_Block("|V", Cur_Pos, EOL_Pos, ALL+NOERR)
Return