There will be many challenges where RsaCtfTool can crack the encryption for you. Print(long_to_bytes('the long number').decode('utf-8')) In order to get the long decrypted integer back into text, just use: from import long_to_bytes Print(long_to_bytes(root).decode('utf-8')) We can then try to find the correct cube root, in order to print out the outcome as UTF-8.

The returned value can then be converted in to string in order to be viewed as plaintext. If we gave a ciphertext we can decrypt it by typing m = pow(c**d %N), which is the same as Message = (Ciphertext^d) modulus N. Given we need numbers to do math, we first have to convert the message/plaintext in to a number value. If we have a plaintext/message (m) then we can encrypt it to a Ciphertext (c) with python by typing c = pow(m**e %N), which is the same as Ciphertext = (Message^e) modulus N. To find the value of phiwe can use python and calculate phi = (p-1)*(q-1).ĭ can then be calculated with python by using this two methods: import gmpy2 The private key is the pair of N and the private exponent d. The public key is the pair of N and the public exponent e. In RSA we need keys for the encryption and decryption. The website alpertron might also be handy.

There is also databases with factorized numbers, like factordb. This might give you the solution without knowing all the factors. In those cases it might be smart to try some basic equations with unkowns. In some cases we can stumble upon variations of the RSA where the primes like pand qand other ones may be reused in calculating other N values. If we have N and either por q, we can find the missing value like this: p = N/q It is possible for N to be the product of more then just two primes, but the conscept is the same by just adding them togheter.

The value of N is the product of the two primes p * q. The most common variables is: p - First factor of the RSA modulus The following is my notes regarding RSA-basics in a CTF (capture the flag)-perspective. It is based on prime numbers and have a way to construct those primes in to values which is used later on in the encryption/decryption-process.

Rsa decrypt python pow