ぱいそんとお友達になろう-csawctf 2011 Crypto3 writeup編-

python練習用にみてた、 @shiracamus氏のCTFのためのパイソン入門というスライドにあった、csawctfの過去問のひとつ。
これだけ少し詰まった（主にpythonでの文字列の操作）ので、メモ。

以下の文字列が問題として渡される。

010011000110000101110011011101000010000001110111011001010110010101101011011100110010000001101101011 001010110010101110100011010010110111001100111001000000111011101100001011100110010000001100001001000 000110011101110010011001010110000101110100001000000111001101110101011000110110001101100101011100110 111001100101110001000000101011101100101001000000111001101100101011001010110110100100000011101000110 111100100000011000100110010100100000011001110110010101101110011001010111001001100001011101000110100 101101110011001110010000001100001001000000110110001101111011101000010000001101111011001100010000001 100010011101010111101001111010001000000110000101100010011011110111010101110100001000000111010001101 000011001010010000001101101011011110111011001100101011011010110010101101110011101000010111000100000 010101000110100001100101001000000110101101100101011110010010000001100110011011110111001000100000011 011100110010101111000011101000010000001110111011001010110010101101011011100110010000001101101011001 010110010101110100011010010110111001100111001000000110100101110011001000000111001001100101011100110 110100101110011011101000110000101101110011000110110010100101110001000000100100101100110001000000111 010001101000011001010111001001100101001000000110100101110011001000000110000101101110011110010110111 101101110011001010010000001100101011011000111001101100101001000000111100101101111011101010010000001 101011011011100110111101110111001000000110111101100110001000000111010001101000011000010111010000100 000011011010110000101111001001000000110001001100101001000000110100101101110011101000110010101110010 011001010111001101110100011001010110010000100000011010010110111000100000011010100110111101101001011 011100110100101101110011001110010000001100010011100100110100101101110011001110010000001110100011010 000110010101101101001000000111010001101111001000000111010001101000011001010010000001101101011001010 110010101110100011010010110111001100111001000000111010001101000011010010111001100100000011101110110 010101100101011010110010111000100000010010010111010000100000011101110110100101101100011011000010000 001100010011001010010000001101000011001010110110001100100001000000111001101100001011011010110010100 100000011101000110100101101101011001010010110000100000011100110110000101101101011001010010000001110 

やることはすぐにおもいつく。2->asciiだろうなぁと
でも2byteずつに区切られておらず、よくみるとところどころにスペースがはいっていたので、
文字列をaに代入し、スペースをけしてbに代入。
んで、8文字ずつに分けるのどうやろう（できればforとか使わずスマートにやりたい）と考えていたところ、Pythonで文字列を2文字ずつ分割する - Python入門
というページを発見。そこのを参考に８文字ずつに分ける。
こんな感じ

list = re.split('(........)',b)

が、空文字が交互に入ってくる。なにかよい解決策があれば教えて下さい......情弱でつらい。ちなみに、後ろの[]の中身の挙動についていまいち理解できてない。普通のlistの動きとはちがうぽ？

上記のとおり、空文字がリストに入ってしまったのでそれを削除。
参考：no workaround: python リストから空の要素を削除

while list.count("") > 0:
         list.remove("")

for使いたくないって言ってたくせにwhile使ってるのはどうなの？とか言ってはいけない

あとはスライドで学んだように操作。
全体の流れはこんな感じ。

>>>a = '
010011000110000101110011011101000010000001110111011001010110010101101011011100110010000001101101011 001010110010101110100011010010110111001100111001000000111011101100001011100110010000001100001001000 000110011101110010011001010110000101110100001000000111001101110101011000110110001101100101011100110 111001100101110001000000101011101100101001000000111001101100101011001010110110100100000011101000110 111100100000011000100110010100100000011001110110010101101110011001010111001001100001011101000110100 101101110011001110010000001100001001000000110110001101111011101000010000001101111011001100010000001 100010011101010111101001111010001000000110000101100010011011110111010101110100001000000111010001101 000011001010010000001101101011011110111011001100101011011010110010101101110011101000010111000100000 010101000110100001100101001000000110101101100101011110010010000001100110011011110111001000100000011 011100110010101111000011101000010000001110111011001010110010101101011011100110010000001101101011001 010110010101110100011010010110111001100111001000000110100101110011001000000111001001100101011100110 110100101110011011101000110000101101110011000110110010100101110001000000100100101100110001000000111 010001101000011001010111001001100101001000000110100101110011001000000110000101101110011110010110111 101101110011001010010000001100101011011000111001101100101001000000111100101101111011101010010000001 101011011011100110111101110111001000000110111101100110001000000111010001101000011000010111010000100 000011011010110000101111001001000000110001001100101001000000110100101101110011101000110010101110010 011001010111001101110100011001010110010000100000011010010110111000100000011010100110111101101001011 011100110100101101110011001110010000001100010011100100110100101101110011001110010000001110100011010 000110010101101101001000000111010001101111001000000111010001101000011001010010000001101101011001010 110010101110100011010010110111001100111001000000111010001101000011010010111001100100000011101110110 010101100101011010110010111000100000010010010111010000100000011101110110100101101100011011000010000 001100010011001010010000001101000011001010110110001100100001000000111001101100001011011010110010100 100000011101000110100101101101011001010010110000100000011100110110000101101101011001010010000001110 '
>>>b = a.replace(' ','')
>>>import re
>>>list = re.split('(........)',b)
>>>while list.count("") > 0:
....       list.remove("")
>>>int2 = lambda s: int(s,2)
>>>map(chr,map(int2,list))
>>>''.join(map(chr,map(int2,list)))
'Last weeks meeting was a great success. We seem to be generating a lot of buzz about the movement. The key for next weeks meeting is resistance. If there is anyone else you know of that may be interested in joining bring them to the meeting this week. It will be held same time, same place.'

すっごい久々に触ってみたけどpython、便利ですね。もっとpython力と文字列操作力というかプログラミング力つけたい。（つけねば）

もっとスマートな解き方あれば、ぜひ教えて下さい。ツッコミとかも（優しくね）