Implementing-cryptography-using-python

Chapter 1 ■ Introduction to Cryptography and Python 29
Figure 1.4: Module methods
Now that you understand the importance of Python modules, let’s import
the hashlib library and then use the MD5 and SHA message digests. Type the
following in Python:
>>> import hashlib
>>> hashlib.md5('hello world'.encode()).hexdigest()
'5eb63bbbe01eeed093cb22bb8f5acdc3'
>>> hashlib.sha512('hello world'.encode()).hexdigest()
'309ecc489c12d6eb4cc40f50c902f2b4d0ed77ee511a7c7a9bcd3ca86d4cd86f
989dd35bc5ff499670da34255b45b0cfd830e81f605dcf7dc5542e93ae9cd76f'
NOTE
are hashed.
Python 3 and higher require that Unicode objects be encoded before they
Creating a Reverse Cipher
For this next exercise, we build on what we have learned in this chapter by creating
a function named reverseCipher that accepts one parameter: plaintext.
We can then call our function and pass the plaintext into it and print out the
return ciphertext. Our method modifies the plaintext so that the ciphertext is
the complete reverse:
def reverseCipher(plaintext):
ciphertext = ''
i = len(plaintext) - 1
while i >= 0:
ciphertext = ciphertext + plaintext[i]
i = i - 1
return ciphertext
plaintext = 'If you want to keep a secret, you must also hide it from
yourself.'
ciphertext = reverseCipher (plaintext)
print(ciphertext)
This code should produce the following result:
.flesruoy morf ti edih osla tsum uoy ,terces a peek ot tnaw uoy fI