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Bill Buchanan
2022-02-03 14:10:19 +00:00
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unit02_symmetric/lab/possible_ans.md
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## Q1
You may need to install "Crypto" with:
<pre>
pip install pycrypto
</pre>
And Padding with:
<pre>
pip install padding
</pre>
Note: The Padding library has not implemented the fully range of padding methods.
```python
from Crypto.Cipher import AES
import hashlib
import sys
import binascii
import Padding
val='hello'
password='hello'
plaintext=val
def encrypt(plaintext,key, mode):
encobj = AES.new(key,mode)
return(encobj.encrypt(plaintext))
def decrypt(ciphertext,key, mode):
encobj = AES.new(key,mode)
return(encobj.decrypt(ciphertext))
key = hashlib.sha256(password.encode()).digest()
plaintext = Padding.appendPadding(plaintext,blocksize=Padding.AES_blocksize,mode='CMS')
print ("After padding (CMS): ",binascii.hexlify(bytearray(plaintext.encode())))
ciphertext = encrypt(plaintext.encode(),key,AES.MODE_ECB)
print ("Cipher (ECB): ",binascii.hexlify(bytearray(ciphertext)))
plaintext = decrypt(ciphertext,key,AES.MODE_ECB)
plaintext = Padding.removePadding(plaintext.decode(),mode='CMS')
print (" decrypt: ",plaintext)
plaintext=val
### Other padding methods have not been implemented in the library
plaintext = Padding.appendPadding(plaintext,blocksize=Padding.AES_blocksize,mode='ZeroLen')
print ("After padding (CMS): ",binascii.hexlify(bytearray(plaintext.encode())))
ciphertext = encrypt(plaintext.encode(),key,AES.MODE_ECB)
print ("Cipher (ECB): ",binascii.hexlify(bytearray(ciphertext)))
plaintext = decrypt(ciphertext,key,AES.MODE_ECB)
plaintext = Padding.removePadding(plaintext.decode(),mode='ZeroLen')
print (" decrypt: ",plaintext)
plaintext=val
plaintext = Padding.appendPadding(plaintext,blocksize=Padding.AES_blocksize,mode='Space')
print ("After padding (CMS): ",binascii.hexlify(bytearray(plaintext.encode())))
ciphertext = encrypt(plaintext.encode(),key,AES.MODE_ECB)
print ("Cipher (ECB): ",binascii.hexlify(bytearray(ciphertext)))
plaintext = decrypt(ciphertext,key,AES.MODE_ECB)
plaintext = Padding.removePadding(plaintext.decode(),mode='Space')
print (" decrypt: ",plaintext)
plaintext=val
plaintext = Padding.appendPadding(plaintext,blocksize=Padding.AES_blocksize,mode='Random')
print ("After padding (Random): ",binascii.hexlify(bytearray(plaintext.encode())))
ciphertext = encrypt(plaintext.encode(),key,AES.MODE_ECB)
print ("Cipher (ECB): ",binascii.hexlify(bytearray(ciphertext)))
plaintext = decrypt(ciphertext,key,AES.MODE_ECB)
plaintext = Padding.removePadding(plaintext.decode(),mode='Random')
print (" decrypt: ",plaintext)
```
An example is [here](https://repl.it/@billbuchanan/ch02ans01#main.py).
## Q2