NeverEnCode

from pwn import *

## The in order list of chars being used for the encryption cipher
algorithmns_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~ !\"#$%&'()*+,-./0123456789:;<=>?@"


## Pass in the offset (shift) the program is using this run through and the encrypted text
## decrypt it
def decrypt(encrypted, index):
    global algorithmns_list
    solved = ''
    for c in encrypted:
        plain_char_posn = (algorithmns_list.index(c) - offset) % len(algorithmns_list)
        solved += algorithmns_list[plain_char_posn]

    return solved


## Find the offset (shift) being used for this run through
def find_offset(result):
    global algorithmns_list
    index = algorithmns_list.index(result)
    return index


## connect and receive banner
conn = remote('neverending.tuctf.com', 12345)



## solve over and over until we reach 50 solves
count = 1
while True:

    banner = conn.recvuntil('text:')

    ## send an A and receive what A encrypts to
    conn.send('A\r\n')
    result = conn.recvline()
    #strip away everything but the encrypted result
    result = result[-3]

    ##find the offset for this current attempt
    offset = find_offset(result)

    ## receive the encrypted text to solve
    solve = conn.recvline()
    conn.recvuntil(':')

    ## cut out the superfluous crap  received along with the solve string
    solve = solve[8:-12]

    ## attempt to decrypt the string
    solution = decrypt(solve, offset)


    ## send solution and check if its right
    print 'Sending solution: %s' %(solution)
    conn.sendline(solution)


    ## Once we reach 50 solves, print stop and receive all text back from the server to get the flag
    if count == 50:
        result = conn.recvall()
        print result
        break

    else:
        conn.recvline()

    count += 1

conn.close()