In today’s world security and privacy of data is a major concern when it comes to transacting with people via mobile applications. Also not all data can be sent via the internet due to unavailability of data connection in mobile phones at all times. To cater to such a requirement of an offline means of performing a transaction in a secure manner, we have developed an Android API. The project constitutes the construction of an API that follows a strict protocol with a well-defined message format that enables a developer to create a pair of apps that can securely communicate with each other. For end-to-end security of the data we have employed the use of the RSA algorithm to sign the data being sent. For enabling offline exchange of messages we have used QR codes (also provided the option of Bluetooth). The API is simple and requires only a method call with the data to be sent from the developer’s side for each phase respectively. This makes it easy for the developer to not worry about the implementation details of the API and can concentrate on only handling the data at the developer’s end. In this attempt to ensure security, our API also includes the concept of conflict resolution when a situation of disagreement in the data arises. We have a provision for resolving the conflict in favour of one of the communicating parties without the involvement of a third-party (i.e. offline). Also there is a provision for the user to acquire control in case of handling certain situations like a conflict or stale data or unapproved data to be sent to the other party. Thus we have attempted to make an API that can securely exchange messages between two parties in an offline manner.