Answer:
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Step-by-step explanation:
1) Assembly language code for Encryption using rotate operations.
INCLUDE Irvine32.inc
INCLUDE Macros.inc
BufSize = 80
.data
key BYTE 6, 4, 1, 2, 7, 5, 2, 4, 3, 6
myText BYTE "This text is going to be encrypted.", 0
buffer BYTE BufSize DUP(?),0,0
stdInHandle HANDLE ?
bytesRead DWORD ?
.code
main PROC
;Pass the pointer to the text string in EDX,
MOV EDX, OFFSET myText
;the array size to ECX
MOV ECX, SIZEOF myText
;pointer to the key array in ESI,
MOV ESI, OFFSET key
;the direction value (0 or 1) in EBX
MOV EBX, 0 ; rotate left for encryption
call WriteString
call Crlf
call encDecText
call WriteString
call Crlf
MOV EBX, 1
call encDecText
call WriteString
call Crlf
;bonus - get string from console and encrypt
mWriteln "Write a text to be encrypted."
; Get handle to standard input
INVOKE GetStdHandle, STD_INPUT_HANDLE
mov stdInHandle,eax
; Wait for user input
INVOKE ReadConsole, stdInHandle, ADDR buffer,
BufSize, ADDR bytesRead, 0
;encrypt and output to console
MOV EDX, OFFSET buffer
MOV ECX, BufSize
MOV EBX, 0
call encDecText
call WriteString
call Crlf
;decrypt and output to console
MOV EBX, 1
call encDecText
call WriteString
INVOKE ExitProcess,0 ; end the program
main ENDP
encDecText PROC
;Receives EDX - OFFSET of the text
; ECX - SIZE of the text
; ESI - OFFSET of the key
; EBX - rotation direction 0 for left 1 for right
PUSHAD
CMP EBX, 0
JE equals
MOV EBX, ESI
ADD EBX, 9 ;the length of key
loopNotEquals:
MOV AL, [EDX] ; value of the text
PUSH ECX
MOV CL, [ESI] ; value of the key
ROR AL, CL ; ror the text by the key
MOV [EDX], AL
POP ECX
CMP ESI, EBX ; if all the keys are used, reset the offset so it uses the beginning
JE reset1
INC ESI
JMP endReset1
reset1:
SUB ESI, 9
endReset1:
INC EDX
loop loopNotEquals
mWriteln "Input decrypted."
JMP endCMP
equals:
MOV EBX, ESI
ADD EBX, 9 ; the length of key
loopEquals:
MOV AL, [EDX] ; value of the text
PUSH ECX
MOV CL, [ESI] ; value of the key
ROL AL, CL ; rol the text by the key
MOV [EDX], AL
POP ECX
CMP ESI, EBX ; if all the keys are used, reset the offset so it uses the beginning
JE reset2
INC ESI
JMP endReset2
reset2:
SUB ESI, 9
endReset2:
INC EDX
loop loopEquals
mWriteln "Input encrypted."
endCMP:
POPAD
RET
encDecText ENDP
END main
Save the files with .asm extension.