This question already has an answer here:

What are the increased possibilities (if any) of being able to crack a private key given the following:

  1. The associated bitcoin (ECDSA Secp256k1-based) public key is known.
  2. The private key has been used to generate a public key from a different ECDSA curve and that public key is also known.
  3. It is known that the two public keys are derived from the same private key.
  4. It is known which ECDSA curves were used to generate the public keys.
  5. It is known which ECDSA curve was used to generate which public key.

merged by mikeazo Mar 30 '14 at 0:40

This question was merged with Is it possible to weaken a bitcoin private key by “using” it elsewhere? because it is an exact duplicate of that question.

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