[FIXED] Custom encryption algorithm in python

Issue

I have made a string encryption method, but i can't find out how to make a decryption method. My encryption function is below (in python)

def encrypt(text, key):
        cmp=["q","w","e","r","t","y","i","u","p","o","s","a","f","d","h","g","k","j","k","l","z","x","c","v","b","n","m","Q","l","E","W","T","R","U","Y","O","I","A","P","D","S","G","F","J","H","L","K","X","Z","V","C","N","B","`","M","2","1","4","3","6","5","8","7","0","9","=","-","!","~","#","@","%","$","&","^","(","*","_",")"," ","+","[","]","\\","{","}","|",",",".","/","<",">","/"]
        md={}
        c=0
        
        for id in cmp:
            md[id]=c
            c+=1

        keyInFigs=0
        for char in key:
            keyInFigs+=md[char]
        textObj=text
        textInFigs=""
        for char in textObj:
            textInFigs+=str(md[char])+" "
        textInFigs=textInFigs.removesuffix(" ")
        output=""
        for char in textInFigs.split():
            output += str(int(char) * keyInFigs) + " "
        return output

Solution

Let's start by re-writing parts of your algorithm, for clarity:

# these will be needed to decrypt as well

# strings are iterables, no need for a list
cmp = "qwertyiupo" + "safdhgkjkl" + "zxcvbnm" + "QlEWTRUYOIAP" + "DSGFJHLK" + "XZVCNB`M" + "2143658709" + "=-!~#@%$&^(*_)" + " +[]\\{}|,./<>/"

# enumerate is simpler
md = {char: index for index, char in enumerate(cmp)}

def encrypt(text, key):
        # sum is clearer
        keyInFigs = sum(md[char] for char in key)
        
        # no need to loop twice, both operations can be combined
        output = " ".join(str(md[char] * keyInFigs) for char in text)
        return output

From there, we can decrypt, simply applying the same steps in the reverse order:

def decrypt(text, key):
    # this is also needed to decrypt
    keyInFigs = sum(md[char] for char in key)
    
    # the text looks like "1234 4324 545365"
    parts = text.split()
    # divide by the key as int, and find the corresponding character
    decoded_values = [cmp[int(part) // keyInFigs] for part in parts]
    output = "".join(decoded_values)
    return output

>>> k = "foobar"
>>> e = encrypt("Hello world!", k)
>>> e
'2992 136 1904 1904 612 5372 68 612 204 1904 884 4556'
>>> decrypt(e, k)
'Hello world!'

Answered By - njzk2