Flag: `ctfzone{2e71b73d355eac0ce5a90b53bf4c03b2}`

```
from pwn import *

s = remote('crypto-01.v7frkwrfyhsjtbpfcppnu.ctfz.one', 1337)

s.sendafter('Login: ', 'A' * 7 + 'B' * 16 + 'C')
s.sendafter('$ ', 'session --get')

iv, ct = s.recvline().strip().split(':')

# _ = unknown character
# pt[0:16] = '_________AAAAAAA'
# pt[16:32] = 'BBBBBBBBBBBBBBBB'
# pt[32:48] = 'C_______regular\x01'

mask = xor('regular\x01', 'root\x04\x04\x04\x04')
ct = b64d(ct)
ct = ct[:24] + xor(ct[24:32], mask) + ct[32:]

s.sendafter('$ ', 'session --set {}:{}'.format(iv, b64e(ct)))
s.sendafter('$ ', 'cat flag.txt')

print s.recvline().strip()
```