# PicoCTF 2k14 - Web Interception

# cat web_interception.py
import socket

host = 'vuln2014.picoctf.com'
port = 65414

def print_recvdata(data):
 for i in range(0, len(data), kl * 2):
  print '<<< ' + data[i:i + (kl * 2)]

def sendrecv(msg):
 s = socket.socket()
 s.connect((host, port))
 s.recv(1024)
 s.send(msg)
 data = s.recv(1024)
 s.close()
 return data

kl = 16  # key length
cdl = 80 # current data length

for i in range(1, 30):
 msg = 'aa' * i
 data = sendrecv(msg)[:-1]
 dl = len(data)/2 # data length
 if cdl < dl:
  print_recvdata(data)
  print 'Data    = ', dl
  print 'Get     = ', gl
  print 'Message = ', ml
  print 'Secret  = ', sl
  break
 else:
  gl = len('GET /')
  ml = len(msg)/2
  sl = dl - ml - gl # secret length
 print i

pad = sl + kl - gl

found = ''

for i in range(pad - 1, kl - gl, -1):
 msg = 'aa' * i
 print '>>> ' + msg + '..' * (pad - len(msg)/2)
 data = sendrecv(msg)[:-1]
 f = 0 # from block1
 t = (kl * 2) * (sl/kl + 1) # to block1 + #blocks(sl)
 key = data[f:t]
 #print_recvdata(data)
 for j in range(0, 256):
  h = format(j, '02x')
  nh = msg + found + h
  data = sendrecv(nh)[:-1]
  if data[f:t] == key:
   print '>>> ' + nh
   #print_recvdata(data)
   print 'found = \'' + chr(j) + '\''
   found += h
   break

print 'secret_data = \'' + found.decode('hex') + '\''

# python web_interception.py
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11
<<< c2ede3651650defcac13ecd82b7b9e7b
<<< 7a7bc20c2692db821734385bfa01f1db
<<< 7bb2c562649b06c08ae178a597ba85d2
<<< c87adffd4197a50cdc4d47384db2b219
<<< 8e930fb9cdf30c3a2c914731545f9fb3
<<< 695e6035c5752aa0d133f436a7d4475f
Data    =  96
Get     =  5
Message =  11
Secret  =  64
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20
found = ' '
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa2048
found = 'H'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa204854
found = 'T'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454
found = 'T'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa2048545450
found = 'P'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f
found = '/'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f31
found = '1'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e
found = '.'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e31
found = '1'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d
'ound = '
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a
found = '
'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a43
found = 'C'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b
found = 'k'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69
found = 'i'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b6965
found = 'e'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a
found = ':'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20
found = ' '
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a2066
found = 'f'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c
found = 'l'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61
found = 'a'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c6167
found = 'g'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d
found = '='
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d63
found = 'c'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e
found = 'n'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67
found = 'g'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e6772
found = 'r'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e677261
found = 'a'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174
found = 't'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e6772617473
found = 's'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f
found = '_'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e
found = 'n'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f
found = '_'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f79
found = 'y'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75
found = 'u'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f7572
found = 'r'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f
found = '_'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66
found = 'f'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f6669
found = 'i'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f666972
found = 'r'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273
found = 's'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f6669727374
found = 't'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f
found = '_'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f65
found = 'e'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563
found = 'c'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f656362
found = 'b'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f
found = '_'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64
found = 'd'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f6465
found = 'e'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa............................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f646563
found = 'c'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..............................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372
found = 'r'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f6465637279
found = 'y'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa..................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f646563727970
found = 'p'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa....................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372797074
found = 't'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa......................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f6465637279707469
found = 'i'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372797074696f
found = 'o'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaa..........................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372797074696f6e
found = 'n'
>>> aaaaaaaaaaaaaaaaaaaaaaaaaa............................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372797074696f6e0d
'ound = '
>>> aaaaaaaaaaaaaaaaaaaaaaaa..............................................................................................................................
>>> aaaaaaaaaaaaaaaaaaaaaaaa20485454502f312e310d0a436f6f6b69653a20666c61673d636f6e67726174735f6f6e5f796f75725f66697273745f6563625f64656372797074696f6e0d0a
found = '
'
secret_data = ' HTTP/1.1
Cookie: flag=congrats_on_your_first_ecb_decryption
'

Reference

https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation