Help with pow() function

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#1

Hey i am attempting to make a RSA encryption but there is a problem with the encryption. i have figured out it is my pow() function that is not working correctly

I have based my RSA encryption off of this YouTube video (made in python, attempting to port in LUA)

The problem with the pow function, in python you could do:

pow(101, 13, 143)
# returns 140

I have attempted to implement the pow function as such:

local function pow(x, y, z)
	return (x ^ y) % z
end
pow(101, 13, 143)

when calling it with the arguments: 101, 13, 143 it just returns 0
image

Running the code in python it works fine

def custompow(x, y, z):
	return (x ** y) % z # python ** is the same as  ^ in LUA

image

Is there anything I have done wrong (e.g used wrong operator)? Any help is appreciated

#2

Screenshot 2020-10-07 at 1.04.16 AM
maybe lua just can’t handle this big number

1 Like
#3

guess this is an error with LUA? since running the same command in python it returns correct answer (140)
image

#4

RSA requires you to use integers which lua doesn’t use. Use another algorithm which works with doubles or use a BigNumInt library (very slow)

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#5

Lua 5.1 from the manual 2.5.1, modulus is defined as: a % b == a - math.floor(a/b)*b, I think the problem comes from this algorithm.
This is almost certainly a bug and it returns the correct result in Lua 5.3.

(You can use math.fmod which doesn’t have this problem)

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#6

I didnt actually know this, guess i will have to do some more researching. Got any other algorithms? Preferably one that works similar to RSA (Public-key cryptography)