Solution_Pad.py

#usr/bin/python

#Faid Mohammed Amine 
#Fb : piratuer

#Pad 200 pts ( YUBITSEC CTF 2017 )

f = open("encrypted_2","w")

secret = "***REDACTED***"
key = "JdKeVFaSdfCxZ3471ZxCVbN"


startchar = ' ' # 32
endchar = '~'   # 126
modular = ord(endchar) - ord(startchar) + 1

def encrypt(message, key):
    ret = ""
    for i in range(len(message)):
        messagechar = ord(message[i]) - ord(startchar)
        keychar = ord(key[i]) - ord(startchar)
        calculatedchar = (messagechar + keychar) % modular
        convertedchar = chr(calculatedchar + ord(startchar))
        ret += convertedchar
    return ret

#f.write(encrypt(secret,key))
#output : " $:m/+y'v@N3bIzs,yMh9>K,",key "

def decrypt(ciphertext, key):
    retn = []
    for i in range(len(ciphertext)):
        messagechar = ord(ciphertext[i]) - ord(startchar)
        keychar = ord(key[i]) - ord(startchar)
        calculatedchar = (messagechar - keychar) % modular
        convertedchar = chr(calculatedchar + ord(startchar))
        retn.append(convertedchar)
    return "".join(retn)
        
ciphertxt = open('encrypted_2').read()

print decrypt(ciphertxt,key)
#print decrypt("$:m/+y'v@N3bIzs,yMh9>K,",key)

#Thanks