From d51c07097514a60bd2862699b85471770e726101 Mon Sep 17 00:00:00 2001
From: Luxferre <lux@ferre>
Date: Tue, 8 Apr 2025 10:39:13 +0300
Subject: [PATCH] added a TI-74 port

---
 README.md    | 20 ++++++++++++++
 dracondi.b74 | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)
 create mode 100644 dracondi.b74

diff --git a/README.md b/README.md
index 39a0cfe..d24da81 100644
--- a/README.md
+++ b/README.md
@@ -139,6 +139,26 @@ implementation to be considered correct:
 4. The decryption part shall sanitize the ciphertext before processing,
    removing any whitespace and non-letter characters from the input.
 
+TI-74 BASIC port
+----------------
+The [dracondi.b74](dracondi.b74) file in this repository contains a port of the
+cipher to the Texas Instruments TI-74 handheld computer in its native BASIC
+language dialect. This port has been developed and tested on the TI-74S model
+and contains the following limitations:
+
+1. The message length is restricted by the device's line limit.
+2. No message prefiltering is done: enter the plaintext strictly in lowercase,
+without any spaces and non-alphabetical characters.
+3. The resulting ciphertext is divided with spaces every five characters but
+the last group is not autofilled.
+4. When decrypting, you can enter the ciphertext with spaces but no other non-
+alphabetical characters are allowed.
+5. No explicit exit command provided, use the BREAK key to exit the program.
+
+For field operation, this port requires your keyphrases to be hardcoded in the
+line 100 and 110 `DATA` statements. You can change the line numbers as long as
+they remain the first `DATA` statements in the device's program memory.
+
 Credits
 -------
 Created by Luxferre in 2025, released into the public domain with no warranties.
diff --git a/dracondi.b74 b/dracondi.b74
new file mode 100644
index 0000000..a18de82
--- /dev/null
+++ b/dracondi.b74
@@ -0,0 +1,73 @@
+100 DATA firstkeyphrase
+110 DATA secondkeyphrase
+120 PRINT "Initializing keys..."
+130 RANDOMIZE
+140 READ P1$,P2$
+150 CALL KEYGEN(P1$,KA1$)
+160 CALL KEYGEN(P2$,KA2$)
+170 LINPUT "Operation (k/e/d): ";OP$
+180 IF OP$="k" THEN 190 ELSE 220
+190 PRINT "KA1: ";KA1$:PAUSE
+200 PRINT "KA2: ";KA2$:PAUSE
+210 GOTO 170
+220 IF OP$="e" THEN 230 ELSE 270
+230 LINPUT "Msg: ";MSG$:IF MSG$="" THEN 170
+240 CALL DRENC(MSG$,KA1$,KA2$,RES$)
+250 PRINT "Enc: ";RES$:PAUSE
+260 GOTO 230
+270 IF OP$="d" THEN 280 ELSE 170
+280 LINPUT "Msg: ";MSG$:IF MSG$="" THEN 170
+290 CALL DRDEC(MSG$,KA1$,KA2$,RES$)
+300 PRINT "Dec: ";RES$:PAUSE
+310 GOTO 280
+320 SUB DRENC(M$,KA1$,KA2$,RES$)
+330 OFFS=INT(26*RND)
+340 RES$=SEG$(KA1$,OFFS+1,1)
+350 L=LEN(M$):SK=1
+360 FOR I=1 TO L
+370 C$=SEG$(M$,I,1)
+380 CI=POS(KA1$,C$,1)+OFFS
+390 IF CI>26 THEN CI=CI-26
+400 CT$=SEG$(KA1$,CI,1):RES$=RES$&CT$
+410 SK=SK+1
+420 IF SK=5 THEN 430 ELSE 440
+430 SK=0:RES$=RES$&" "
+440 OFFS=POS(KA2$,CT$,1)+I-1
+450 IF OFFS>25 THEN OFFS=OFFS-26*INT(OFFS/26)
+460 NEXT I
+470 SUBEND
+480 SUB DRDEC(M$,KA1$,KA2$,RES$)
+490 OFFS=POS(KA1$,SEG$(M$,1,1),1)-1
+500 M$=SEG$(M$,2,1024)
+510 RES$="":L=LEN(M$):RI=0
+520 FOR I=1 TO L
+530 C$=SEG$(M$,I,1):IF C$=" " THEN 600
+540 RI=RI+1
+550 CI=POS(KA1$,C$,1)-OFFS
+560 IF CI<1 THEN CI=CI+26
+570 RES$=RES$&SEG$(KA1$,CI,1)
+580 OFFS=POS(KA2$,C$,1)+RI-1
+590 IF OFFS>25 THEN OFFS=OFFS-26*INT(OFFS/26)
+600 NEXT I
+610 SUBEND
+620 SUB KEYGEN(P$,KA$)
+630 KA$=""
+640 L=LEN(P$)
+650 FOR I=1 TO L
+660 C$=SEG$(P$,I,1)
+670 IF POS(KA$,C$,1)>0 THEN 680 ELSE 710
+680 CK=ASC(C$)-72:IF CK>25 THEN CK=CK-26
+690 C$=CHR$(97+CK)
+700 GOTO 670
+710 KA$=KA$&C$
+720 NEXT I
+730 KA$=KA$&"abcdefghijklmnopqrstuvwxyz"
+740 KR$="":L2=LEN(KA$)
+750 FOR I=1 TO L2
+760 C$=SEG$(KA$,I,1)
+770 IF POS(KR$,C$,1)=0 THEN KR$=KR$&C$
+780 NEXT I
+790 L=L-INT(L/26)*26
+800 KA$=SEG$(KR$,L+1,26)&SEG$(KR$,1,L)
+810 SUBEND
+820 END