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challenge_15.py
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challenge_15.py
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from functools import reduce
def pkcs7(plaintext, blocksize):
padding = blocksize - len(plaintext) % blocksize
pad = chr(padding)
# print(bytes(''.join((plaintext, pad*padding)),'utf-8'))
return ''.join((plaintext, pad*padding))
text = pkcs7("ICE ICE BABY",16).encode()
text2 = b"ICE ICE BABY\x05\x05\x05\x05"
text3 = b"ICE ICE BABY\x01\x03\x02\x03"
# candidatePadding = 0
# count = 0
blocksize = 16
# for c in text:
# print(c)
# if c < blocksize - 1:
# if count == 0:
# candidatePadding = c
# count+=1
# elif c == candidatePadding:
# count +=1
# else:
# break
# # raise Exception("Sorry, invalid padding")
# if(count == candidatePadding):
# print(text[0:len(text) - count])
# else:
# print("count: " + str(count) + " candidate: " + str(candidatePadding))
# raise Exception("Sorry, invalid padding")
def valid_pkcs(text):
possiblePadding = int.from_bytes(text[-1:],'little')
if possiblePadding == 0:
possiblePadding = 16
val = int.from_bytes(text[-1:], "little")
if all(elem == val for elem in text[-possiblePadding:]):
print(len(text))
return text[:len(text) - possiblePadding]
raise Exception("Sorry, invalid padding")
print(valid_pkcs(text3))