check that the public keys lie on the curve.? #271

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1. tomato42 commented on Nov 27, 2021

   

   tomato42

   on Nov 27, 2021

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   All the public methods in VerifyingKey check if the public key lies on the curve, it's controlled by the validate_point option like:
   

   python-ecdsa/src/ecdsa/keys.py

   Lines 202 to 204 in b3b27cd

   	def from_public_point(
   	cls, point, curve=NIST192p, hashfunc=sha1, validate_point=True
   	):

   
   or:
   

   python-ecdsa/src/ecdsa/keys.py

   Lines 286 to 293 in b3b27cd

   	def from_string(
   	cls,
   	string,
   	curve=NIST192p,
   	hashfunc=sha1,
   	validate_point=True,
   	valid_encodings=None,
   	):

   and how to check that after the operation of multiplication I left the border of the curve?

   if a point was on the curve before multiplication, then the result will be on the curve...

   You can double check that on high level, by exporting the point to a byte string and then create a new VerifyingKey instance, that will verify if it is on curve still.

   On low level, you need to get the CurveFp() and call contains_point() for short Weierstrass curves:
   

   python-ecdsa/src/ecdsa/ellipticcurve.py

   Line 131 in b3b27cd

   def contains_point(self, x, y):

   
   or the contains_point() of CurveEdTw() for twisted Edwards curves:
   

   python-ecdsa/src/ecdsa/ellipticcurve.py

   Line 197 in b3b27cd

   def contains_point(self, x, y):
2. tomato42

   added

   question

   on Nov 27, 2021
3. tlsfuzzer

   locked and limited conversation to collaborators on Nov 27, 2021
4. tomato42

   closed this as completedon Nov 27, 2021