Blinding uses slow algorithm

[tomato42]

The private key operations generate a new blinding factor for every new signature:

python-rsa/rsa/key.py

Lines 440 to 453 in 4beb68d

	def blinded_encrypt(self, message: int) -> int:
	"""Encrypts the message using blinding to prevent side-channel attacks.
	:param message: the message to encrypt
	:type message: int
	:returns: the encrypted message
	:rtype: int
	"""
	blind_r = self._get_blinding_factor()
	blinded = self.blind(message, blind_r) # blind before encrypting
	encrypted = rsa.core.encrypt_int(blinded, self.d, self.n)
	return self.unblind(encrypted, blind_r)

Given that blinding requires calculating inverse modulo of of the blinding factor, it is a slow operation (rule of thumb is that inverse is as costly as calculating 100 modulo multiplications).

The existing literature[1] (section 9) suggests generating a blinding factor, its inverse, and then squaring both of them for next operation.