code: func (s *MemoryKeyStore) GetKey(ski []byte) (bccsp.Key, error) {
  	key, ok := s.store[hex.EncodeToString(ski)]
  	if !ok {
  		return nil, fmt.Errorf("Key not found [%s]", ski)
  	}
  	return key, nil
  }
docs: // GetKey returns a key for the provided SKI