code: public SRTPCryptoContext deriveContext(long ssrc, int roc, long deriveRate) {
  		return new SRTPCryptoContext(ssrc, roc, deriveRate, masterKey, masterSalt, policy);
  	}
docs: Derive a new SRTPCryptoContext for use with a new SSRC
  
  This method returns a new SRTPCryptoContext initialized with the data of
  this SRTPCryptoContext. Replacing the SSRC, Roll-over-Counter, and the
  key derivation rate the application cab use this SRTPCryptoContext to
  encrypt / decrypt a new stream (Synchronization source) inside one RTP
  session.
  
  Before the application can use this SRTPCryptoContext it must call the
  deriveSrtpKeys method.
  
  @param ssrc
  The SSRC for this context
  @param roc
  The Roll-Over-Counter for this context
  @param deriveRate
  The key derivation rate for this context
  @return a new SRTPCryptoContext with all relevant data set.