Implementing-cryptography-using-python

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Chapter 5 ■ Stream Ciphers and Block Ciphers 169iv: öhLÒôÏ2q]>°mâciphertext: BDE+z8ME6r0QgkraNXLuuQ==File Encryption Using AESNext, you can encrypt a file using AES by implementing the following Pythonrecipe. The primary difference is opening the file and passing the packs intoblocks:aes = AES.new(key, AES.MODE_CBC, iv)filesize = os.path.getsize(infile)with open (encrypted, ‘w’) as fout:fout.write(struct.pack(‘<Q’, filesize))fout.write(iv)File Decryption Using AESTo decrypt the previous example, use the following code to reverse the process:with open(verfile, 'w') as fout:while True:data = fin.read(sz)n = len(data)if n == 0:breakdecd = aes.decrypt(data)n = len(decd)if fsz > n:fout.write(decd)else:fout.write(decd[:fsz]) # <- remove padding on last blockfsz -= nSummaryAfter completing this chapter, you should feel comfortable converting betweenhexdigest and plaintext using the binascii library. The binascii module providesseveral methods to convert between ASCII-ended binary expressions andbinary. We then took a survey of how both stream ciphers and block cipherswork. You should understand that a stream cipher is a symmetric key cipherwhere plaintext digits are combined with a pseudorandom cipher digit stream.In a stream cipher, each plaintext digit is encrypted one at a time with thecorresponding digit of the keystream, to give a digit of the ciphertext stream.
170 Chapter 5 ■ Stream Ciphers and Block CiphersWhile most stream ciphers are used at the hardware layer, you now understandhow to both create and use the Salsa20, ChaCha20, and Vernam ciphers.We then turned our focus on block ciphers and the various modes of operations.We concluded the block cipher exploration by examining which modesallow block ciphers to operate like stream ciphers. We also explored how tocreate a DIY cipher using a Feistel Network. We finished with an introductionto the Advanced Encryption Standard (AES) cryptosystem. You will exploremore about block mode operations and AES in the next chapter as you learnto encrypt images.
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ImplementingCryptography UsingPytho
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To Stephanie, Eden, Hayden, and Ken
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viAbout the Authorbook, Shannon is
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Contents at a GlanceIntroductionxvi
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xiiContentsUsing Conditionals 16Usi
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xivContentsPseudorandomness115Break
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xviContentsInstalling and Testing W
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xviiiIntroductionprivacy advocates.
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CHAPTER1Introduction to Cryptograph
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Chapter 1 ■ Introduction to Crypt
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CHAPTER2Cryptographic Protocolsand
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Chapter 2 ■ Cryptographic Protoco
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66 Chapter 3 ■ Classical Cryptogr
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CHAPTER4Cryptographic Mathand Frequ
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Chapter 4 ■ Cryptographic Math an
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220 Chapter 7 ■ Message Integrity
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222 Chapter 7 ■ Message Integrity
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224 Chapter 8 ■ Cryptographic App
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CHAPTER9Mastering CryptographyUsing
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Chapter 9 ■ Mastering Cryptograph
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IndexSYMBOLS\ (backslash), 10- oper
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Index ■ D-D 279CIA Triad, 35-36ci
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Index ■ I-M 281hashlib module, 28
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Index ■ Q-S 283Preneel, Bart, 145
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