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#RSA algorithm
import string
def CharCode(l):
return ord(l) - ord('a')+1
def ModExp(a,e):
'''calculate a^e mod 3233'''
aa, bb = a % 3233, 1
for i in range(e):
bb = aa*bb % 3233
return bb
def toCode(phrase):
'''convert phrase = block of letters
return a code number < 3233
'''
#convert a phrase to a number base 30
sum = 0
for x in phrase:
sum = 30*sum + CharCode(x)
#do the RSA conversion
return ModExp(sum,17)
def toLetters(codedNum):
'''convert codeNum <3233
return a block of letters
'''
#undo the RSA conversion
num = ModExp(codedNum,2753)
#convert a number base 30 to a phrase
ll= []
while num >0:
r , num = num % 30, num / 30
ll.append(string.lowercase[r-1])
ll.reverse()
return "".join(ll)
def codeText(text):
'''text = string
return a list of coded numbers'''
#pad out to the right length with extra letters
if len(text) % 2 ==1:
text += "a"
#cut into blocks
blocks = [text[i:i+2] for i in range(0,len(text),2)]
return [ toCode(ablock ) for ablock in blocks]
qq= codeText('helloworld')
print qq
print "".join([toLetters(block) for block in qq])
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