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75 lines
2.6 KiB
ReStructuredText
75 lines
2.6 KiB
ReStructuredText
Block cipher lab
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################
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:date: 2012-02-14 01:36
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:author: Russell Ballestrini
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:tags: Code, Security, Python
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:slug: block-cipher-lab
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:status: published
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| **Consider the following block cipher.** Suppose that each block
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cipher T simply reverses the order of the eight input bits (so that,
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for example 11110000 becomes 00001111).
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| Further suppose that the 64-bit scrambler does not modify any bits.
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With n = 3 iterations and the original 64-bit input equal to 10100000
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repeated eight times, what is the value of the output?
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| Now change the last bit of the original 64-bit input from 0 to a 1.
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Now suppose that the 64-bit scrambler inverses the order of the 64
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bits.
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| **Solution in python:**
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::
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def chunks( l, n ):
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"""accept a list and chuck size, return chunks"""
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return [ l[ i:i+n ] for i in range( 0, len(l), n ) ]
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def T( blocks ):
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"""for each block, reverse block, return blocks"""
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result = []
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for block in blocks:
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result.append( ''.join( [bit for bit in reversed( block )] ) )
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return result
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def scrambler( input ):
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"""inverse the order of input"""
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return ''.join( [i for i in reversed( input ) ] )
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def cipher1( input, n = 3, chunk_length = 8 ):
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"""make chucks out of input, reverse each chunk return result"""
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blocks = chunks( input, chunk_length )
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for i in range( 0, n ): blocks = T( blocks )
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return ''.join( blocks )
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def cipher2( input, n = 3, chunk_length = 8 ):
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"""same as cipher1 but with scrambler"""
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blocks = chunks( input, chunk_length )
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for i in range( 0, n ):
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blocks = T( blocks )
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blocks = chunks( scrambler( ''.join( blocks ) ), chunk_length )
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return ''.join( blocks )
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if __name__ == "__main__":
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input = "1010000010100000101000001010000010100000101000001010000010100000"
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print cipher1( input )
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# output: 0000010100000101000001010000010100000101000001010000010100000101
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input = "1010000010100000101000001010000010100000101000001010000010100001"
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print cipher1( input )
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# output: 0000010100000101000001010000010100000101000001010000010110000101
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input = "1010000010100000101000001010000010100000101000001010000010100000"
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print cipher2( input )
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# output: 1010000010100000101000001010000010100000101000001010000010100000
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input = "1010000010100000101000001010000010100000101000001010000010100001"
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print cipher2( input )
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# output: 1010000110100000101000001010000010100000101000001010000010100000
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.. contents::
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