PhaseStream 1 Writeup

Solved by: Legend

• Each character will be XOR with each character of the key and the length of the key is 5 characters.

    start =  bytearray.fromhex('2e313f2702')  #Randomly tried from starting of given cipher
    text = 'CHTB{'.encode()
    
    key = b''
    output = b''
    
    for i in range(len(start)):
            key += bytes([text[i] ^ start[i]])
    
    print('Key: ' + str(key))
    print('Key len: '+ str(len(key)))
    print('Key type: ' + str(type(key)))
    print('Key hex: ' + key.hex())
    
    for i in range(int(len(start))):
            output += bytes([start[i] ^ key[i % len(key)]])
    
    print('2e313f2702 --> '+ '(' + output.hex() + ')' + ' == ' + str(output) + '(text)')
    
    shifr  = bytearray.fromhex('2e313f2702184c5a0b1e321205550e03261b094d5c171f56011904')
    
    output2 = b''
    
    for i in range(len(shifr)):
            output2 += bytes([shifr[i] ^ key[i % len(key)]])
    
    output_dec = output2.decode(errors='ignore')
    
    print('Flag: '+ output_dec)
    print('Flag hex: '+ output.hex())

Flag: CHTB{u51ng_kn0wn_pl41nt3xt}