I have been reading up on RSA attacks and came across a problem that could be called a most-significant-bit (MSB) oracle attack.
For the sake of clarity, let's define RSA primes $(p, q)$, private key d and the public key $(e, N)$ where N is the modulus.
Now assume an oracle exists that will decrypt a given ciphertext $C$ using the private key d and checks the decrypted cipher -- it will return true or false if the decrypted cipher's most significant bit is 1 or 0.
How can I achieve such an attack while given a challenge cipher $C$! http://www.cits.rub.de/imperia/md/content/may/hw2.pdf