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Can someone explain to me what exactly this line does, when I try to understand it, I end up curling up even more:
#Vars definidas:
import sys
key = sys.argv[2]
mode = sys.argv[3]
posiçãoDoChar = 0
xored = ''
for char in msg:
xored += chr(ord(key[posiçãoDoChar%len(key)]) ^ ord(char)) # ESTÁ LINHA EXATAMENTE
posiçãoDoChar += 1
print(xored)
3
The line makes some function calls and an "xor" operation, using the operator ^ - and concatenates the result into a string he calls "xored".
we can unfold in parts to make it easier to understand:
xored += chr(ord(key[posiçãoDoChar%len(key)]) ^ ord(char))
is the same as:
posicao_da_letra_da_chave = posicaoDoChar % len(key)
# O "modulo" - "%" é o resto da divisão -entao
# se sua chave tem 4 letras, quando
# estiver na letra "5", 5%4 vale 1:
# a letra na posicao "1" da chave é reutilizada, e assim por diante.
letra_da_chave = key[posicao_da_letra_da_chave]
codigo_numerico_da_letra_da_chave = ord(letra_da_chave) # converte o caractere em seu código numérico UNICODE (se for um caractere ASCII, isso é equivalente ao código ASCII)
codigo_numerico_da_letra_da_mensagem = ord(char)
codigo_numerico_cifrado = codigo_numerico_da_letra_da_chave ^ codigo_numerico_da_letra_da_mensagem # Operação de transformação reversível usando 'xor'
nova_letra = chr(codigo_numerico_cifrado)
xored += nova_letra # contatena a nova letra na mensagem cifrada final
So, in fact, when we unfold, only that line makes 8 distinct operations.
The key of the process is the "xor", made with the operator " ": this is an operation made bit by bit between the two values: if one of the two values is "1" and the other "0" the result is "1". If the two values are equal, the result is "0". This operation has an interesting property that it is reversible: if I make a "xor" of an X number that I have, with a Y number, the result is a different number "Z". If I take back Z with Y, the result is "X" - which is why this algorithm can retrieve the original message - in decryption, each encrypted character will undergo an xor with the same letter as the key with which it was "scanned" in the encryption operation.
Here the XOR working with numerical variables:
In [10]: x = 43254
In [11]: y = 64636
In [12]: z = x ^ y
In [13]: z
Out[13]: 21642
In [14]: y ^ z
Out[14]: 43254
In [15]: y ^ z == x
Out[15]: True
And again, but this time using the prefix 0b and the call bin to visualize the process by seeing the numbers in binary:
In [16]: x = 0b11110000
In [17]: y = 0b10101010
In [18]: z = x ^ y
In [19]: bin(z)
Out[19]: '0b1011010'
In [20]: bin(z ^ y)
Out[20]: '0b11110000'
I still have some difficulties, until why the var will receive an info that was processed by 8 methods, more so now became clearer the understanding, business is now practice, thank you very brother, helped me mto...
If you can understand how these 8 operations are on that first line, you can already understand a lot - try to read the descriptions of the operations I did from the end to the beginning - it’s kind of like what happens on that line. Like, "oh, I’m going to do the xor of a value from the original message with a value that came from the key." How do I get these values? Ah - on the top line he calls the "Ord" - and so on.
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