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python help needed |
stranac
Member
Posts: 124
Location: Croatia
Joined: 15.11.08
Rank: God |
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I'm trying to make a program that will xor a file with a preset key (and do some more minor stuff) and then save it as a .jpg.
I got a working program now, but the problem is it only does it for the first 1156 bytes (and doing it right), like the rest isn't there (the original file is 20kB in size).
So here's the code :
# xoring a file with string 'secret'
from operator import xor
key = list('secret')
for i in range (6) :
key[i] = ord(key[i])
index = 0
f = open ('data.bin')
g = open ('xored.jpg', 'w')
data = list(f.read())
f.close()
for i in range (20426) :
hex = ord(data[i])
if index==6 :
index = 0
rez = xor (hex, key[index])
if rez == 23 :
rez = 0
elif rez == 0 :
rez = 23
elif rez == 78 :
rez = 66
elif rez == 66 :
rez = 78
elif rez == 36 :
rez = 144
elif rez == 144 :
rez = 36
rez = chr (rez)
index = index + 1
g.write (rez)
g.close()
Any help is welcome, and so are suggestions on optimizing my programing. |
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| Author |
RE: python help needed |
stranac
Member
Posts: 124
Location: Croatia
Joined: 15.11.08
Rank: God |
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Sorry, just wasn't thinking. It's a binary file and i forgot to append b to the file mode (rb & wb).
Edited by stranac on 20-05-09 13:29 |
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| Author |
RE: python help needed |
ynori7
Future Emperor of Earth
Posts: 1481
Location: #valhalla
Joined: 08.10.07
Rank: Diabolical |
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for i in range (20426):
Maybe I'm misunderstanding something here, but if this is tracing through the file, you're only going through the first 2KB. Since data is a list, you could do this instead to ensure all data is modified:
for i in data:
Also, importing xor from operator and using that as a method is unnecessary. The xor operator is built in, you use the ^ symbol:
>>> ord('d')
100
>>> ord('a')
97
>>> 100^97
5
>>> from operator import xor
>>> xor(100, 97)
5
Also, instead of looping through your list and applying ord to it, you could just use the built in map function:
map(ord, key)
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| Author |
RE: python help needed |
stranac
Member
Posts: 124
Location: Croatia
Joined: 15.11.08
Rank: God |
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ynori7 wrote:
for i in range (20426):
Maybe I'm misunderstanding something here, but if this is tracing through the file, you're only going through the first 2KB. Since data is a list, you could do this instead to ensure all data is modified:
for i in data:
Actually it's 20kB but yes, you're right about the alternative, it is better.
ynori7 wrote:
Also, importing xor from operator and using that as a method is unnecessary. The xor operator is built in, you use the ^ symbol:
>>> ord('d')
100
>>> ord('a')
97
>>> 100^97
5
>>> from operator import xor
>>> xor(100, 97)
5
Also, instead of looping through your list and applying ord to it, you could just use the built in map function:
map(ord, key)
This is some stuff I didn't know. I'm glad someone told me about it, and I'm of to do some research on map.
Thanks for your help. |
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| Author |
RE: python help needed |
ynori7
Future Emperor of Earth
Posts: 1481
Location: #valhalla
Joined: 08.10.07
Rank: Diabolical |
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stranac wrote:
Actually it's 20kB but yes, you're right about the alternative, it is better.
Whoops, I was counting that as bits. Anyway, 20KB is 20480 bytes, not 20426. But like I said it's best to use "for i in list" because you probably don't know exactly how many characters are in your list.
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