Android Question How to implement a XOR between array of bytes

prbmjr · Apr 21, 2021

Hi everyone,

I must implement a XOR operation between arrays of bytes, because I need to implement a special data encryption requeted by my client..

I found only the bit.xor function between integers, Is there a way to implement a XOR with arrays?

Thank you in advance!

br,

Paulo Bueno

prbmjr · Apr 21, 2021

For reference, it would be a function like numpy.bitwise_xor (python) - https://numpy.org/doc/stable/refere....html?highlight=bitwise_xor#numpy.bitwise_xor

Erel · Apr 22, 2021

B4X:

Sub ArrayXor (b1() As Byte, b2() As Byte) As Byte()
    'assuming that the arrays are with the same length
    Dim b3(b1.Length) As Byte
    For i = 0 To b1.Length - 1
        b3(i) = Bit.Xor(b1(i), b2(i))
    Next
    Return b3
End Sub

prbmjr · Apr 22, 2021

Erel said:

B4X:

Sub ArrayXor (b1() As Byte, b2() As Byte) As Byte()
    'assuming that the arrays are with the same length
    Dim b3(b1.Length) As Byte
    For i = 0 To b1.Length - 1
        b3(i) = Bit.Xor(b1(i), b2(i))
    Next
    Return b3
End Sub

Hi Erel,

Thank you very much for your answer. I had something like this already implemented, but my concern is about the performance, if I have to use this type of code instead a real function/library using big arrays, like 500k, 50mb, etc... These arrays are entires files that must be encrypted... I have a similar code in python for reference and this runs really fast using the function numpy.bitwise_xor . I will try and I let you know with the result.

br,

Paulo Bueno

Erel · Apr 22, 2021

Test it.

B4X:

Dim b1(500000), b2(500000) As Byte
For i = 1 To 100
    Dim n As Long = DateTime.Now
    ArrayXor(b1, b2)
    Log(DateTime.Now - n)
Next

On my device it takes between 0 to 1 millisecond.

prbmjr · Apr 22, 2021

Erel said:
Test it.

B4X:

Dim b1(500000), b2(500000) As Byte For i = 1 To 100 Dim n As Long = DateTime.Now ArrayXor(b1, b2) Log(DateTime.Now - n) Next

On my device it takes between 0 to 1 millisecond.

Hi Erel,

I tested with this code:

B4X:

Sub ArrayXor_teste As Byte()
    'assuming that the arrays are with the same length
    Dim b1(552643), b2(552643) As Byte
    Dim b3(b1.Length) As Byte

    For i = 0 To b1.Length - 1
        
        b3(i) = Bit.Xor(b1(i), b2(i))
    Next
    Return b3
End Sub

In my test I used a Sansung S8 device and takes 32 seg, why??

DonManfred · Apr 22, 2021

prbmjr said:
In my test I used a Sansung S8 device and takes 32 seg, why??

Did you tested it in RELEASE mode?? NEVER do performance measures in DEBUG mode.

prbmjr · Apr 22, 2021

DonManfred said:
Did you tested it in RELEASE mode?? NEVER do performance messures in DEBUG mode.

Hi,

No, In debug mode, I will test in release mode now...

Thank you!

DonManfred · Apr 22, 2021

i did a quick test in one app of mine.
As the app does other things in parallel too i got 135ms as result. Still FAST; 0,135 Seconds.

prbmjr · Apr 22, 2021

DonManfred said:
i did a quick test in one app of mine.
As the app does other things in parallel too i got 135ms as result. Still FAST; 0,135 Seconds.

Hi,

I tested in release mode and all process is quite fast now..

Android Question How to implement a XOR between array of bytes

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