mirror of
https://github.com/bvanroll/odiseectf.git
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83 lines
2.6 KiB
Python
83 lines
2.6 KiB
Python
import sys
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import os
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import getpass
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from Crypto.Cipher import AES
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# from Crypto.Random import get_random_bytes, random
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# from Crypto.Util import Padding
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from Crypto.Hash import MD5, SHA256
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# generates key based on password
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def generatekey():
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password = getpass.getpass('Password for decryption: ')
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h = MD5.new()
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h.update(''.join(password))
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return h.digest()
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# calculates and return hash for message
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def calculatehash(message):
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h = SHA256.new()
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h.update(message)
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# use hexdigest to prevent problems with control characters
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# e.g. \r in charcter 5, appends 4, then overwrites beginning of message with rest of digest
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return h.hexdigest()
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# check integrity and return cleartext or error message
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def checkintegrity(decryptedcontent):
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return calculatehash(decryptedcontent[0:-64]) == decryptedcontent[-64:]
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# encrypts content in AES CBC mode
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def decrypt_AES_CBC(inputfilename, encryptedContent):
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# create encrypted filename, keep extension
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outputfilename = inputfilename[0:inputfilename.find('.', len(inputfilename) - 5)] + '_decrypted' + inputfilename[
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inputfilename.find(
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'.'):len(
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inputfilename)]
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key = generatekey()
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decipher = AES.new(key, AES.MODE_CBC)
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decryptedcontent = decipher.decrypt(encryptedContent)
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ivlength = 16
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# remove iv and padding
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decryptedcontent = decryptedcontent[ivlength:-ord(decryptedcontent[-1])]
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# check Integrity and retain cleartext
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if checkintegrity(decryptedcontent):
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cleartext = decryptedcontent[0:-64]
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else:
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cleartext = 'Integrity check error'
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# useful only for decrypted text files
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# print(cleartext)
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# write to file
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outputfile = open(outputfilename, 'wb')
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outputfile.write(cleartext)
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outputfile.close()
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for i in sys.argv[1:]:
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inputfilename = i
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try:
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inputfile = open(inputfilename, 'rb')
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except IOError:
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print("File " + inputfilename + " not found, working directory: " + os.getcwd())
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continue
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else:
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# if file opened, read content into variable
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content = inputfile.read()
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inputfile.close()
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# apply symmetric encryption
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decrypt_AES_CBC(inputfilename, content)
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# encrypt_AES_ECB(inputfilename,content)
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