I’m attempting to implement the TEA algorithm in assembly language (8086 TASM). However, I’m encountering difficulties in two areas

1. String Input: I need assistance in implementing a mechanism to input strings from the user within my assembly program.

2. Hexadecimal Conversion: After obtaining user input, I aim to convert each letter of the input string into its corresponding hexadecimal representation to prepare it for TEA encryption. I’m seeking guidance on how to accomplish this conversion efficiently.

3. Encrypted Message Decryption: Following encryption using the TEA algorithm, I’m encountering difficulty in converting the resulting encrypted message back into readable string letters. I require assistance in decrypting and converting the encrypted message into its original form.

I’ve successfully implemented the encrypt and decrypt functions for the TEA algorithm. These functions seem to perform encryption and decryption operations correctly. However, I’m stuck at handling string input and converting them into a format suitable for encryption. Additionally, after encryption, the output contains unknown symbols, and I need assistance in converting it into readable encrypted strings.

Here is my encrypt / decrypt functions:

proc encrypt
    pusha

    mov cx, 32
    encryptLoop:
        ; sum += delta
        mov ax, [delta]
        add [sum], ax

        xor eax,eax
        ; ((p2 << 4) + k0)
        mov dx, [p2]
        shl dx, 4
        add dx, [k0]

        ; (p2 + sum)
        mov bx, [p2]
        add bx, [sum]

        ; ((p2 << 4) + k0) ^ (p2 + sum)
        xor dx, bx

        xor bx, bx

        ; ((p2 >> 5) + k1)
        mov bx, [p2]
        shr bx, 5
        add bx, [k1]
        ; ((p2 << 4) + k0) ^ (p2 + sum) ^ ((p2 >> 5) + k1)
        xor dx, bx
        add [pe1], dx

        ; ((p1 << 4) + k2)
        mov dx, [p1]
        shl dx, 4
        add dx, [k2]

        ; (p1 + sum)
        mov bx, [p1]
        add bx, [sum]

        ; ((p0 << 4) + k2) ^ (p0 + sum)
        xor dx, bx

        xor bx, bx

        ; ((p1 >> 5 ) + k3)
        mov bx,[p1]
        shr bx, 5
        add bx, [k3] 
        ; ((p0 << 4) + k2) ^ (p0 + sum) ^ ((p1 >> 5 ) + k3)
        xor dx, bx

        add [pe2], dx
    loop encryptLoop

    popa
    ret
endp encrypt

proc decrypt
   pusha

    mov cx, 32
    decryptLoop:
        ; ((p1 << 4) + k2)
        mov dx, [p1]
        shl dx, 4
        add dx, [k2]

        ; (p1 + sum)
        mov bx, [p1]
        add bx, [sum]

        ; ((p0 << 4) + k2) ^ (p0 + sum)
        xor dx, bx

        xor bx, bx

        ; ((p1 >> 5 ) + k3)
        mov bx,[p1]
        shr bx, 5
        add bx, [k3] 
        ; ((p0 << 4) + k2) ^ (p0 + sum) ^ ((p1 >> 5 ) + k3)
        xor dx, bx

        sub [pe2], dx

        xor ax,ax
        ; ((p2 << 4) + k0)
        mov dx, [p2]
        shl dx, 4
        add dx, [k0]

        ; (p2 + sum)
        mov bx, [p2]
        add bx, [sum]
        
        ; ((p1 << 4) + k0) ^ (p1 + sum)
        xor dx, bx

        xor bx, bx

        ; ((p2 >> 5) + k1)
        mov bx, [p2]
        shr bx, 5
        add bx, [k1]
        ; ((p2 << 4) + k0) ^ (p2 + sum) ^ ((p2 >> 5) + k1)
        xor dx, bx
        sub [pe1], dx

        ; sum -= delta
        mov ax, [delta]
        sub [sum], ax
    loop decryptLoop

    popa

    ret
endp decrypt

DS section:

delta dw 79b9h ; 79b9h for 16 bits, 9e3779b9h for 32 bits

sum dw 0
p1 dw 0
p2 dw 0

k0  dw 0                  
k1  dw 0                   
k2  dw 0                   
k3  dw 0         

; Two part of the plaintext after encryption
pe1 dw 0
pe2 dw 0