Is it okay to use a variable-time RSA implementation to verify TLS certificates?
Two answers to the question:


It is about principles and reusability of the cryptographic primitives. Once there are implemented by insecure manner, nothing prevents reusing or misusing the insecure functionality later.
TLS validation (during the SSL handshake) involves a secret as well - during the SSL handshake a piece of data is encrypted and sent over to decrypt to proof ownership of the private key. This is the part when the side-channel attack needs to be mitigated.


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