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672 lines
16 KiB
Markdown
672 lines
16 KiB
Markdown
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# Lab 2: Symmetric Key
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Objective: The key objective of this lab is to understand the range of symmetric key methods used within symmetric key encryption. We will introduce block ciphers, stream ciphers and padding. The key tools used include OpenSSL, Python and JavaScript. Overall Python 2.7 has been used for the sample examples, but it should be easy to convert these to Python 3.x.
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Lab Demo: [here](https://youtu.be/N3UADaXmOik)
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## A OpenSSL
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OpenSSL is a standard tool that we used in encryption. It supports many of the standard symmetric key methods, including AES, 3DES and ChaCha20.
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### A.1
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Using:
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* openssl list-cipher-commands
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* openssl version
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Outline five encryption methods that are supported:
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Outline the version of OpenSSL:
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### A.2
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Using openssl and the command in the form:
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<pre>
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openssl prime –hex 1111
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</pre>
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Check if the following are prime numbers:
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* 42 [Yes][No]
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* 1421 [Yes][No]
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### A.3
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Now create a file named myfile.txt (using nano).
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Next encrypt with aes-256-cbc
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<pre>
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openssl enc -aes-256-cbc -in myfile.txt -out encrypted.bin
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</pre>
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and enter your password.
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Use the following command to view the output file:
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<pre>
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cat encrypted.bin
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</pre>
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Is it easy to write out or transmit the output: [Yes][No]
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### A.4
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Now repeat the previous command and add the –base64 option.
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<pre>
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openssl enc -aes-256-cbc -in myfile.txt -out encrypted.bin –base64
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</pre>
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Use following command to view the output file:
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<pre>
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cat encrypted.bin
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</pre>
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Is it easy to write out or transmit the output: [Yes][No]
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### A.5
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Now Repeat the previous command and observe the encrypted output.
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<pre>
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openssl enc -aes-256-cbc -in myfile.txt -out encrypted.bin –base64
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</pre>
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Has the output changed? [Yes][No]
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Why has it changed?
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### A.6
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Now let's decrypt the encrypted file with the correct format:
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<pre>
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openssl enc -d -aes-256-cbc -in encrypted.bin -pass pass:napier -base64
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</pre>
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Has the output been decrypted correctly?
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What happens when you use the wrong password?
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### A.7
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Now encrypt a file with Blowfish and see if you can decrypt it.
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Did you manage to decrypt the file? [Yes][No]
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## B Padding (AES)
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With encryption, we normally use a block cipher, and where we must pad the end blocks to make sure that the data fits into a whole number of block. Some background material is here:
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Web link (Padding): http://asecuritysite.com/encryption/padding
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In the first part of this tutorial we will investigate padding blocks:
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### B.1
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With AES which uses a 256-bit key, what is the normal block size (in bytes).
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Block size (bytes):
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Number of hex characters for block size:
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### B.2
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Go to: Web link (AES Padding): http://asecuritysite.com/encryption/padding
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Using 256-bit AES encryption, and a message of “kettle” and a password of “oxtail”, determine the cipher using the differing padding methods (you only need to show the first six hex characters).
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If you like, copy and paste the Python code from the page, and run it on your Ubuntu instance.
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CMS:
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Null:
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Space:
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### B.3
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For the following words, estimate how many hex characters will be used for the 256-bit AES encryption:
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Number of hex characters:
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“fox”:
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“foxtrot”:
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“foxtrotanteater”:
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“foxtrotanteatercastle”:
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### B.4
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With 256-bit AES, for n characters in a string, how would you generalise the calculation of the number of hex characters in the cipher text.
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How many Base-64 characters would be used (remember 6 bits are used to represent a Base-64 character): Hex characters:
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Base-64 characters:
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## C Padding (DES)
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In the first part of this lab we will investigate padding blocks.
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### C.1
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With DES which uses a 64-bit key, what is the normal block size (in bytes):
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Block size (bytes):
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Number of hex characters for block size:
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### C.2
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Go to: Web link (DES Padding): http://asecuritysite.com/encryption/padding_des
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Using 64-bit DES key encryption, and a message of “kettle” and a password of “oxtail”, determine the cipher using the differing padding methods.
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If you like, copy and paste the Python code from the page, and run it on your Ubuntu instance.
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CMS:
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Null:
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Space:
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### C.3
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For the following words, estimate how many hex characters will be used for the 64-bit key DES encryption:
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Number of hex characters:
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“fox”:
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“foxtrot”:
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“foxtrotanteater”:
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“foxtrotanteatercastle”:
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### C.4
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With 64-bit DES, for n characters in a string, how would you generalise the calculation of the number of hex characters in the cipher text.
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How many Base-64 characters would be used (remember 6 bits are used to represent a Base-64 character): Hex characters:
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Base-64 characters:
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## D Python Coding (Encrypting)
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In this part of the lab, we will investigate the usage of Python code to perform different padding methods and using AES. First download the code from:
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Web link (Cipher code): http://asecuritysite.com/cipher01.zip
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The code should be:
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```python
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from Crypto.Cipher import AES
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import hashlib
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import sys
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import binascii
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import Padding
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val='hello'
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password='hello'
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plaintext=val
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def encrypt(plaintext,key, mode):
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encobj = AES.new(key,mode)
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return(encobj.encrypt(plaintext))
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def decrypt(ciphertext,key, mode):
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encobj = AES.new(key,mode)
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return(encobj.decrypt(ciphertext))
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key = hashlib.sha256(password).digest()
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plaintext = Padding.appendPadding(plaintext,blocksize=Padding.AES_blocksize,mode='CMS')
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print "After padding (CMS): "+binascii.hexlify(bytearray(plaintext))
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ciphertext = encrypt(plaintext,key,AES.MODE_ECB)
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print "Cipher (ECB): "+binascii.hexlify(bytearray(ciphertext))
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plaintext = decrypt(ciphertext,key,AES.MODE_ECB)
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plaintext = Padding.removePadding(plaintext,mode='CMS')
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print " decrypt: "+plaintext
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plaintext=val
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```
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Now update the code so that you can enter a string and the program will show the cipher text. The format will be something like:
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<pre>
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python cipher01.py hello mykey
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</pre>
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where “hello” is the plain text, and “mykey” is the key. A possible integration is:
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```python
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import sys
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if (len(sys.argv)>1):
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val=sys.argv[1]
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if (len(sys.argv)>2):
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password=sys.argv[2]
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```
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Now determine the cipher text for the following (the first example has already been completed):
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Message Key CMS Cipher
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“hello” “hello123”
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0a7ec77951291795bac6690c9e7f4c0d
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“inkwell” “orange”
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“security” “qwerty”
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“Africa” “changeme”
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Now copy your code and modify it so that it implements 64-bit DES and complete the table (Ref to: http://asecuritysite.com/encryption/padding_des):
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Message Key CMS Cipher
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“hello” “hello123” 8f770898ddb9fb38
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“inkwell” “orange”
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“security” “qwerty”
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“Africa” “changeme”
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Now modify the code so that the user can enter the values from the keyboard, such as with:
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```python
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cipher=raw_input('Enter cipher:')
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password=raw_input('Enter password:')
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```
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## E Python Coding (Decrypting)
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Now modify your coding for 256-bit AES ECB encryption, so that you can enter the cipher text, and an encryption key, and the code will decrypt to provide the result. You should use CMS for padding. With this, determine the plaintext for the following (note, all the plain text values are countries around the World):
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CMS Cipher (256-bit AES ECB) Key Plain text
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b436bd84d16db330359edebf49725c62 “hello”
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4bb2eb68fccd6187ef8738c40de12a6b “ankle”
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029c4dd71cdae632ec33e2be7674cc14 “changeme”
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d8f11e13d25771e83898efdbad0e522c “123456”
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Now modify your coding for 64-bit DES ECB encryption, so that you can enter the cipher text, and an encryption key, and the code will decrypt to provide the result. You should use CMS for padding. With this, determine the plaintext for the following (note, all the plain text values are countries around the World):
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CMS Cipher (64-bit DES ECB) Key Plain text
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f37ee42f2267458d “hello”
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67b7d1162394b868 “ankle”
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ac9feb702ba2ecc0 “changeme”
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de89513fbd17d0dc “123456”
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Now update your program, so that it takes a cipher string in Base-64 and converts it to a hex string and then decrypts it. From this now decrypt the following Base-64 encoded cipher streams (which should give countries of the World):
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CMS Cipher (256-bit AES ECB) Key Plain text
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/vA6BD+ZXu8j6KrTHi1Y+w== “hello”
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nitTRpxMhGlaRkuyXWYxtA== “ankle”
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irwjGCAu+mmdNeu6Hq6ciw== “changeme”
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5I71KpfT6RdM/xhUJ5IKCQ== “123456”
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PS … remember to add "import base64".
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## F Catching exceptions
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If we try “1jDmCTD1IfbXbyyHgAyrdg==” with a passphrase of “hello”, we should get a country. What happens when we try the wrong passphrase?
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Output when we use “hello”:
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Output when we use “hello1”:
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Now catch the exception with an exception handler:
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```python
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try:
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plaintext = Padding.removePadding(plaintext,mode='CMS')
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print " decrypt: "+plaintext
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except:
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print("Error!")
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```
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Now implement a Python program which will try various keys for a cipher text input, and show the decrypted text. The keys tried should be:
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["hello","ankle","changeme","123456"]
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Run the program and try to crack:
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<pre>
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1jDmCTD1IfbXbyyHgAyrdg==
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</pre>
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What is the password:
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## G Stream Ciphers
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The Chacha20 cipher is a stream cipher which uses a 256-bit key and a 64-bit nonce (salt value). Currently AES has a virtual monopoly on secret key encryption. There would be major problems, though, if this was cracked. Along with this AES has been shown to be weak around cache-collision attacks. Google thus propose ChaCha20 as an alternative, and actively use it within TLS connections. Currently it is three times faster than software-enabled AES and is not sensitive to timing attacks. It operates by creating a key stream which is then X-ORed with the plaintext. It has been standardised with RFC 7539.
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### G.1 We can use node.js to implement ChaCha20:
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```javascript
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var chacha20 = require("chacha20");
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var crypto = require('crypto');
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var keyname="test";
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var plaintext = "testing";
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var args = process.argv;
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if (args.length>2) plaintext=args[2];
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if (args.length>3) keyname=args[3];
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var key = crypto.createHash('sha256').update(keyname).digest();
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var nonce = new Buffer.alloc(8);
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nonce.fill(0);
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console.log( key);
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var ciphertext = chacha20.encrypt(key, nonce, new Buffer.from(plaintext));
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console.log("Ciphertext:\t",ciphertext.toString("hex"));
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console.log("Decipher\t",chacha20.decrypt(key,
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nonce, ciphertext).toString());
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```
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If we use a key of "qwerty", can you find the well-known fruits (in lower case) of the following ChaCha20 cipher streams:
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<pre>
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e47a2bfe646a
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ea783afc66
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e96924f16d6e
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</pre>
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What are the fruits?
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What can you say about the length of the cipher stream as related to the plaintext?
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How are we generating the key and what is the key length?
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What is the first two bytes of the key if we use a pass-phrase of “qwerty”?
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What is the salt used in the same code?
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How would you change the program so that the cipher stream was shown in in Base64?
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How many bits will the salt use? You may have to look at the node.js documentation on the method for this.
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### G.2
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RC4 is a standard stream cipher and can be used for light-weight cryptography. It can have a variable key size. The following is a node.js implementation:
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```javascript
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// RC4
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var crypto = require('crypto');
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var keyname="test";
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var plaintext = "testing";
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var args = process.argv;
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if (args.length>2) plaintext=args[2];
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if (args.length>3) keyname=args[3];
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var key = crypto.createHash('sha256').update(keyname).digest();
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var cipher = crypto.createCipheriv('rc4', key,'' );
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var ciphertext = cipher.update( plaintext, 'utf8', 'hex');
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console.log("Ciphertext:\t",ciphertext);
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var decipher = crypto.createDecipheriv('rc4', key,'' );
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var text = decipher.update( ciphertext, 'hex','utf8');
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console.log("Decipher:\t",text);
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```
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For a password of "napier", find out the fruits used for these RC4 cipher streams:
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<pre>
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8d1cc8bdf6da
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911adbb2e6dda57cdaad
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8907deba
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</pre>
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What are the fruits?
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What happens to the cipher when you add an IV (salt) string?
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For light-weight cryptography, what is the advantage of having a variable key size:
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How might we change the program to implement RC4 with a 128-bit key?
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## H Node.js for encryption
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Node.js can be used as a back-end encryption method. In the following we use the crypto module (which can be installed with “npm crypto”, if it has not been installed). The following defines a message, a passphrase and the encryption method.
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```javascript
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var crypto = require("crypto");
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function encryptText(algor, key, iv, text, encoding) {
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var cipher = crypto.createCipheriv(algor, key, iv);
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encoding = encoding || "binary";
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var result = cipher.update(text, "utf8", encoding);
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result += cipher.final(encoding);
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return result;
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}
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function decryptText(algor, key, iv, text, encoding) {
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var decipher = crypto.createDecipheriv(algor, key, iv);
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encoding = encoding || "binary";
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var result = decipher.update(text, encoding);
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result += decipher.final();
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return result;
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}
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var data = "This is a test";
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var password = "hello";
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var algorithm = "aes256"
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#const args = process.argv.slice(3);
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#data = args[0];
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#password = args[1];
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#algorithm = args[2];
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console.log("\nText:\t\t" + data);
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console.log("Password:\t" + password);
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console.log("Type:\t\t" + algorithm);
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var hash,key;
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if (algorithm.includes("256"))
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{
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hash = crypto.createHash('sha256');
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hash.update(password);
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key = new Buffer.alloc(32,hash.digest('hex'),'hex');
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}
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else if (algorithm.includes("192"))
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{
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hash = crypto.createHash('sha192');
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hash.update(password);
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key = new Buffer.alloc(24,hash.digest('hex'),'hex');
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}
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else if (algorithm.includes("128"))
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{
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hash = crypto.createHash('md5');
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hash.update(password);
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key = new Buffer.alloc(16,hash.digest('hex'),'hex');
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}
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const iv=new Buffer.alloc(16,crypto.pseudoRandomBytes(16));
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console.log("Key:\t\t"+key.toString('base64'));
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console.log("Salt:\t\t"+iv.toString('base64'));
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var encText = encryptText(algorithm, key, iv, data, "base64");
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console.log("\n================");
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console.log("\nEncrypted:\t" + encText);
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var decText = decryptText(algorithm, key, iv, encText, "base64");
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console.log("\nDecrypted:\t" + decText);
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```
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Save the file as "h_01.js" and run the program with:
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<pre>
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node h_01.js
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</pre>
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Now complete the following table:
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Text Pass phrase Type Ciphertext and salt (just define first four characters of each)
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This is a test hello Aes128
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France Qwerty123 Aes192
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Germany Testing123 Aes256
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Now reset the IV (the salt value) to an empty string (“”), and complete the table:
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||
|
||
Text Pass phrase Type Ciphertext
|
||
|
||
This is a test hello Aes128
|
||
|
||
France Qwerty123 Aes192
|
||
|
||
Germany Testing123 Aes256
|
||
|
||
|
||
Does the ciphertext change when we have a fixed IV value?
|
||
|
||
|
||
Using an Internet search, list ten other encryption algorithms which can be used with createCipheriv:
|
||
|
||
|
||
|
||
|
||
|
||
## I Reflective questions
|
||
1. If we have five ‘a’ values (“aaaaa”). What will be the padding value used for 256-bit AES with CMS:
|
||
|
||
|
||
|
||
|
||
|
||
2. If we have six ‘a’ values (“aaaaaa”). What will be the hex values used for the plain text:
|
||
|
||
|
||
|
||
|
||
|
||
3. The following cipher text is 256-bit AES ECB for a number of spaces (0x20):
|
||
|
||
<pre>
|
||
c3f791fad9f9392116b2d12c8f6c4b3dc3f791fad9f9392116b2d12c8f6c4b3dc3f791fad9f9392116b2d12c8f6c4b3dc3f791fad9f9392116b2d12c8f6c4b3da3c788929dd8a9022bf04ebf1c98a4e4
|
||
</pre>
|
||
|
||
What can you observe from the cipher text:
|
||
|
||
|
||
|
||
What is the range that is possible for the number of spaces which have been used:
|
||
|
||
|
||
|
||
How might you crack a byte stream sequence like this:
|
||
|
||
|
||
|
||
|
||
|
||
4. For ChaCha20, we only generate a key stream. How is the ciphertext then created:
|
||
|
||
|
||
|
||
|
||
|
||
## J What I should have learnt from this lab?
|
||
The key things learnt:
|
||
|
||
• How to encrypt and decrypt with symmetric key encryption, and where we use a passphrase to generate the encryption key.
|
||
• How padding is used within the encryption and decryption processes.
|
||
• The core difference between a block cipher and a stream cipher.
|
||
|
||
## Notes
|
||
The code can be downloaded from:
|
||
|
||
git clone https://github.com/billbuchanan/esecurity
|
||
|
||
If you need to update the code, go into the esecurity folder, and run:
|
||
|
||
git pull
|
||
|
||
To install a Python library use:
|
||
|
||
pip install libname
|
||
|
||
To install a Node.js package, use:
|
||
|
||
npm install libname
|
||
|
||
## Possible solutions
|
||
Have a look at: https://github.com/billbuchanan/esecurity/blob/master/unit02_symmetric/lab/possible_ans.md
|
||
|