Abstract: This invention provides for the encoding of synchronization information in the transmitted streamed data so that the receiver and transmitter may synchronize their internal cipher states. It uses a random number generator at the transmitter subsystem as well as one-way cryptographic hash functions, and streaming cipher algorithms at both the transmitter subsystem and the receiver subsystem. The output of the random number generator at the transmitter is included in the transmitted data packet, and data in the packet is encrypted using a key derived from this same output value. Since this derivation is carried out using a number of encryption steps, such as a one-way hash function and a streaming cipher algorithm, to produce a key that is then used to encrypt the data before it is transmitted, the value of this key is of little use in decrypting the message.

Abstract: This invention provides an improved mechanism to guard against message sequencing threats. It can be used in any system which makes use of a transform which uses a state machine such as encryption/decryption and compression/decompression systems, and where the transform and the inverse transform use the same state machines. The invention is implemented as a matching pair of applications at both ends of a transmission link. The transmitting end encodes the current value of a particular state using a one-way hash function and adds this value as a field in the transmitted packet. At the receiving end, the packet is passed to the decoding algorithm which derives the current value of the same state, and passes it through the same one way hash function. The receiver can compare the result of these operations with the value in the field sent by the transmitting end.

Abstract: The invention allows the introduction in real-time of at least sufficient security to minimize the risk of intruders overhearing data on a particular link. This reduces the risk of being victim to either a Type 1—Unauthorized access threat or a Type 3—Message sequencing threat. The method involves encryption at the physical data link level where the form of the encryption affects groups of data bits. The effect of introducing the invention is to add noise to the signal in such a way that it can be subtracted from the received signal leaving only the original signal. The resulting signal, were it to be observed by a person other than the intended recipient, would have an effective Signal to Noise (S/N) ratio of less than 1. The masking effect of this added ‘noise’ signal hides the original signal from any eavesdroppers, since it well-known in the art that for a non-periodic signal to be effectively recovered it must have a S/N greater than 1.