;Project $2-$ Encryption and Decryption message using encryption key and special

logic.

;The line with "Add code here" need to supply the LC$-3$ Instruction for asm program

run success.

;Algorithm

;

;The encryption algorithm is as follows. Each ASCII code in the message will be

transformed as follows:

;

; $1.$The low order bit of the code will be toggled. That is$,$ if it is a $1,$

; it will be replaced by a $0,$ if it is a $0,$ it will be replaced by a $1.$

;

; $2.$ The key will be added to the result of step $1$ above.

; For example, if the input $($plain text$)$ is A and the encryption key is $6,$

; the program should take the ASCII value of A$,01000001,$ toggle bit $[0$:$0],$

; producing $01000000$ and then add the encryption key, $6.$

; The final output character would be $01000110,$ which is the ASCII value F$.$

;

;The decryption algorithm is the reverse. That is$,$

; $1.$Subtract the encryption key from the ASCII code. $2.$ Toggle the low order bit

of the result of step $1.$

; For example, if the input $($cipher text$)$ is F$,$ and the encryption key is $6,$

; we first subtract the encryption key $($i$.$e$.,$ we add $-6)$ from the ASCII value

of F$,$

; $01000110+11111010,$ yielding $01000000.$ We then toggle bit $[0$:$0],$

; producing $01000001,$ which is the ASCII value for A$.$

;

;The result of the encryption$/$decryption algorithm should be stored in locations

x$3116$ to x$3129.$

;

;Output

;

;Your program should output the encrypted or decrypted message to the screen.

;Note that the encryption$/$decryption algorithm stored the message to be output

starting in location x$3116.$

$.$ORIG x$3000$

AND R$0,$ R$0,$ #$0$ ;Clear R$0$

AND R$1,$ R$1,$ #$0$ ;Clear R$1$

AND R$2,$ R$2,$ #$0$ ;Clear R$2$

AND R$3,$ R$3,$ #$0$ ;Clear R$3$

AND R$4,$ R$4,$ #$0$ ;Clear R$4$

AND R$5,$ R$5,$ #$0$ ;Clear R$5$

AND R$6,$ R$6,$ #$0$ ;Clear R$6$

LD R$1,$ STORE ; Sets R$1$ to x$3100$ for memory storage and access

LEA R$0,$ PROMPT$1$ ; Load Prompt$1"($E$)$ncryption or $($D$)$ecryption

PUTS ; Output Prompt$1$ same as TRAP $22.$ Write null$-$

terminated string to console.

IN ; Get character input from keyboard same as

TRAP $20$

STR R$0,$ R$1,$ #$0$ ; Stores$/$write character at memory location

indicated by R$1$

LEA R$0,$ PROMPT$2$ ; Load Prompt$2$ Encryption Key $"0-9"$

PUTS ; Output Prompt$2$ same as TRAP $22$

IN ; Get character input from keyboard same as

TRAP $20$