python replace multiple characters in a string

Question

I want to encrypt a string in python. Every character in the char is mapped to some other character in the secret key. For example 'a' is mapped to 'D', 'b' is mapped to 'd', 'c' is mapped to '1' and so forth as shown below:

char    = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
secretkey="Dd18Abz2EqNPWhYTOjBvtVlpXaH6msFUICg4o0KZwJeryQx3f9kSinRu5L7cGM"

If I choose the string "Lets meet at the usual place at 9 am" the output must be "oABjMWAABMDBMB2AMvjvDPMYPD1AMDBMGMDW"

I'm curious as to how much security this would provide? Over on security SE they always recommend using third-party encryption options and not trying to reinvent the wheel. Have you researched encryption before doing this? — Dom
– Dom, Commented Feb 24, 2016 at 15:18

130333 · Accepted Answer · 2016-02-24 16:04:34Z

3

As for replacing multiple characters in a string

You can use str.maketrans and str.translate:

>>> char = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
>>> secretkey = "Dd18Abz2EqNPWhYTOjBvtVlpXaH6msFUICg4o0KZwJeryQx3f9kSinRu5L7cGM"
>>> trans = str.maketrans(char, secretkey)  
>>> s = "Lets meet at the usual place at 9 am"
>>> s.translate(trans)
'0AvB WAAv Dv v2A tBtDP TPD1A Dv M DW'

or if you prefer to preserve only those in char:

>>> ''.join(c for c in s if c in char).translate(trans)
'0AvBWAAvDvv2AtBtDPTPD1ADvMDW'

As for encrypting

I would recommend using a dedicated library for that, such as pycrypto.

edited Feb 24, 2016 at 16:04

answered Feb 24, 2016 at 15:13

130333

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Comments

Yanick Nedderhoff · Accepted Answer · 2016-02-24 13:04:40Z

0

Ok, I am making two assumptions here.

I think the output you expect is wrong, for instance L should be mapped to 0, not to o, right?
I am assuming you want to ignore whitespace, since it is not included in your mapping.

So then the code would be:

to_encrypt = "Lets meet at the usual place at 9 am"
char = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
secretkey = "Dd18Abz2EqNPWhYTOjBvtVlpXaH6msFUICg4o0KZwJeryQx3f9kSinRu5L7cGM"
encrypted = ""

for c in to_encrypt:
    if c in char:
        encrypted += secretkey[char.index(c)]

print(encrypted)

The output would be:

0AvBWAAvDvv2AtBtDPTPD1ADvMDW

edited Feb 24, 2016 at 13:04

answered Feb 24, 2016 at 12:59

Yanick Nedderhoff

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1 Comment

Gabriel Bogatu Over a year ago

Thank you very much! With your help i solve the problem

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