Greeting, I am trying to run this assembly program. I get the error "Source.asm(56): error A2070: invalid instruction operands" (XOR buffer[ESI],key[EDX] ). Can you, please, help me fix this problem and anything that I may have missed? Do I have to use PUSHAD and POPHD too? I got the code from the solution from chapter 6.11.2, problem 8 Message Encryption, and it has the same error. Thanks.

; This program clears the screen, creates the key and inputs ; plain text from the user, encrypts plain text and display it, ; decrypt the cipher text and display it

INCLUDE Irvine32.inc

BUFFMAX = 128

.data strPlainText BYTE "Enter the plain text:",0 strEncrptPlainText BYTE "The encrypt plain text is:",0 strDecrptPlainText BYTE "The Decrypt cipher text is:",0 buffer BYTE BUFFMAX+1 DUP(0) buffSize DWORD ? key BYTE "ABXmv#7" keySize DWORD 7

.code

main PROC ;call the procedures

CALL Clrscr ;clear the screen CALL InputPlainText ;input plain text from the user CALL ConvertText MOV EDX, OFFSET strEncrptPlainText CALL DisplayText ;display encrypted text

CALL ConvertText MOV EDX, OFFSET strDecrptPlainText ;display decrypted text CALL DisplayText exit main ENDP

InputPlainText PROC USES ECX EDX ;input the plain text, receive and return nothing MOV EDX, OFFSET strPlainText CALL WriteString ;write the string strPlainText CALL Crlf MOV ECX, BUFFMAX ;store the length of maximum buffer MOV EDX, OFFSET buffer CALL ReadString ;read the buffer

MOV buffSize, EAX ;store the input buffer CALL Crlf RET InputPlainText ENDP

ConvertText PROC USES ESI ECX EDX ;encrypt the text and decrypt the cipher text, receive and return nothing

MOV ECX, buffSize ;convert each character of buffer text MOV EDX, 0 ;initialize index of key string MOV ESI, 0 ;initialize index of buffer string

L1: XOR buffer[ESI],key[EDX] ;convert the buffer text INC ESI ;increment ESI register INC EDX ;increment EDX register

CMP EDX, keySize ;compare if EDX equals keySize JE L2 ;jump to L2 JMP L1

L2: MOV EDX, 0 ;reinitialize index to 0 LOOP L1

RET

ConvertText ENDP

DisplayText PROC USES EDX ;display the encrypt and decrypt text

MOV EDX, OFFSET buffer CALL WriteString ;write the content of buffer CALL Crlf CALL Crlf

RET DisplayText ENDP

END main