code: func NewSigncryptSealStream(ciphertext io.Writer, ephemeralKeyCreator EphemeralKeyCreator, sender SigningSecretKey, receiverBoxKeys []BoxPublicKey, receiverSymmetricKeys []ReceiverSymmetricKey) (io.WriteCloser, error) {
  	return newSigncryptSealStream(ciphertext, sender, receiverBoxKeys, receiverSymmetricKeys, ephemeralKeyCreator, defaultSigncryptRNG{})
  }
docs: // NewSigncryptSealStream creates a stream that consumes plaintext data. It
  // will write out signed and encrypted data to the io.Writer passed in as
  // ciphertext. The encryption is from the specified sender, and is encrypted
  // for the given receivers.
  //
  // ephemeralKeyCreator should be the last argument; it's the 2nd one
  // to preserve the public API.
  //
  // If initialization succeeds, returns an io.WriteCloser that accepts
  // plaintext data to be encrypted and a nil error. Otherwise, returns
  // nil and the initialization error.