The present invention relates to a method and a system for securely transmitting data, particularly using encryption of packetized data and multi-channel transmission.

When electronically transmitting data, for example through a computer network, it is generally desirable to protect the transmitted content from being captured and read by an unauthorized third party. This is important for reasons of privacy protection for communications containing sensitive private information, but essential for the transmission of commercial data, such as data relating to e-commerce, communication within companies for protecting business secrets, privileged attorney-client communication, or governmental and military communication.

A wide variety of possibilities to encrypt data communication is available, including symmetric encryption or encryption using public keys, using standards such as the Advanced Encryption Standard (AES) or publicly available applications like Pretty Good Privacy (PGP).

A method for securely storing and transmitting data is described in EP 1 732 259 A1 which discloses generating a random sequence of characters as a key stream as a one-time pad. The keystream is bitwise combined with plaintext using an exclusive-OR operation to create ciphertext. The keystream and ciphertext are routed over physically separate communication paths to a receiving host, which decrypts by applying the keystream to the ciphertext using exclusive-OR.

WO 2012/139174 A1 and EP 2 555 466 A1 relate to the distribution of cryptographic keys and teach using a quantum channel for distributing and synchronizing bits used as one-time pad.

There is still a need to further increase the security of data transmission, and to provide a convenient system that allows encryption at a very high level.

The present invention is defined by the appended independent claims; the dependent claims describe embodiments of the invention.

The transmission method of the present invention allows secure transmission of a data stream between a sender and a recipient, and further allows multi-user transmission between multiple senders to multiple recipients. According to the invention the sender receives a data stream. The data stream may be received by the sender from a user equipment (UE), such as a personal computer, mobile device, or a server distributing, e.g. media content. The transmission between the UE and the sender may be performed in any known way, such as wired or wireless using e.g. LAN, WLAN or mobile communication standards. Alternatively, the UE, e.g. a mobile device, may be configured as the sender to prepare and transmit the data stream. The bit stream to be transmitted is packetized at the sender into a plurality of data packets that may have the same or varying sizes. The packetizing may use already existing packets, such as internet protocol (IP) packets. Alternatively, proprietary packetizing may be performed, such as collecting data into packets up to a predefined size (resulting in packets of equal size) or collecting bits during a predefined time (packets of varying sizes).

Each data packet is split into at least two subpackets. The subpackets are formed such that the information of the underlying data packet can be restored from a combination of the subpackets only, the individual subpackets include unusable information.

Preferably, two subpackets are formed from each data packet. This may be achieved by encrypting the data packet using a random key, preferably a symmetrical key such as used in AES encryption. In this case, the key represents one of the subpackets while the encrypted data represent the other one of the two subpackets. Restoring the original data packet is only possible with both subpackets, by using the key to decrypt the encrypted subpacket.

Alternatively, secret sharing may be used to form the at least two subpackets that again are only useful in combination to restore the original information.

Before being transmitted, a one-time pad is overlaid over the subpackets, and the encrypted subpackets are transmitted to the receiver.

The sender and the receiver are connected at least via two distinct transmission paths. The different paths may use different transmission technologies, such as wireless or wired transmission. The paths may also be locally separated by using, for example, different transmission cables, or may use different frequencies for wireless transmission, and/or may be temporarily separated. Radio transmission may also be used a transmission path. That is, the data transmission may be wireless using for example GSM, UMTS, LTE or via a radio network, or wired using for example DSL.

The sender and the receiver are the components which are installed at the respective user's site, preferably without installation of further IT components, i.e. on a plug & play basis.

The sender and the receiver may be part of a single system, i.e. each user may have a system having a sender and a receiver installed therein. This way each user has sending and receiving capabilities.

Two of the encrypted subpackets formed from an individual data packet are transmitted via different transmission paths. In the preferred case of two subpackets being formed from each data packet, one of the encrypted subpackets is transmitted over a first transmission path and the other one of the two encrypted subpackets is transmitted over a second transmission path from the sender to the receiver.

At the receiver, the encrypted subpackets are decrypted using an identical copy of the one-time pad held by the receiver and the information of the data packets is restored by using the combined information of the subpackets being formed from each data packet.

The invention further provides a system for securely transmitting a data stream. The system comprises at least one sender, at least one recipient, and at least two different transmission paths. The sender and the recipient are configured to perform the transmission method of the invention.

The keys used for splitting the data packets in the embodiment using symmetric encryption may be pregenerated at the sender and stored in a key buffer. Furthermore, the keys are transmitted to the receiver. Also at the receiver, a key buffer is provided for storing the transmitted keys. Later, when data packets should be transmitted, the keys stored in the key buffers at the sender and at the receiver can be used to encrypt and decrypt the data packets without the need of simultaneously transmitting the corresponding keys. Thereby, also in the case a transmission channel used for transmitting the keys is unavailable, e.g. due to transmission problems or an attack to this channel, the encrypted data, i.e. the second subpacket, can be transmitted on another transmission path and the communication can continue uninterrupted.

According to the present invention, all subpackets are additionally overlaid with a one-time pad. This applies to both the key and the encrypted data when using symmetric encryption for splitting the data packets, and also for the different subpackets formed using secret sharing. The random numbers of the one-time pad must be available at the sender, and, in an identical copy, at the receiver. Preferably, the bits of the one-time pad are generated quantum mechanically, using a quantum random number generator (QRNG). A huge amount of random numbers may be pregenerated as one-time pad data and stored in a memory provided at the sender. An identical copy of the one-time pad may be produced and transferred to receiver side. Each time subpackets are to be transmitted, the subpacket may then be overlaid with a portion of the pregenerated one-time pad data. The one-time pad data stored in the memories at the sender and the receiver must be regularly replaced in order to assure that each portion of the one-time pad data is only used once.

For example, two identical copies of quantum mechanically generated random numbers may be centrally produced and transferred to the sender and the receiver. In order to further increase security, the identical copies may be stored on two memory devices, e.g. hard discs, that are shipped and installed to the sender and the receiver. In order to avoid the need to frequently replace the memory devices, devices with sufficient storage space should be used, such as hard drives having disc spaces of 500 GB or more. If the one-time pad data is “consumed” before the memories have been replaced, permutations of the stored random numbers may be used. This, however, leads to a decrease of the level of security that depends on the size of the stored one-time pad data.

According to an embodiment of the invention, a portable or mobile device may be configured as the sender and/or the recipient, e.g. a cell phone, a tablet or a notebook computer. As storage still is an issue for mobile devices, only limited space may be assigned for storing the one-time pad data. In order to regularly update the one-time pad data in a mobile device, the “complete” one-time pad data, identically stored at the sender and the receiver, may be locally stored in a memory at or connected to a docking station, e.g. a docking station that is used to regularly charge the mobile device. Each time the mobile device is connected to the docking station, a portion of the one-time pad data may be transferred to the mobile device for subsequent use.

