Method and System for determining a cryptographic key

A system for determining a cryptographic key, comprising:

• at least one input/output device for inputting a cyphertext and outputting the cryptographic key;
• at least one tensor network with parameters representing a candidate cryptographic key;
• an optimiser for adjusting the parameters of the at least one tensor network by classical optimisation;
• and
• a comparator for determining an overlap between the target ciphertext and the candidate ciphertext.

Computer system for determining a cryptographic key, the computer system comprising a classical processor configured to:

• construct a tensor network with parameters representing a candidate cryptographic key;
• adjust the parameters of the tensor network;
• generate a new candidate key sample and obtaining a candidate ciphertext obtained with the candidate cryptographic key;
• calculate a cost function with respect to a target ciphertext;
• measure an overlap between the target ciphertext and the candidate ciphertext,
• determine whether the overlap has reached a threshold value is reached;
• and
• if threshold value is not reached, repeat the method by further adjusting the parameters of the tensor network, if the threshold value is reached, determine that the candidate cryptographic key is the cryptographic key.

A computer program product comprising logic for executing, by means of a classical processor, a method for determining a cryptographic key, the method comprising the steps of:

• constructing a tensor network with parameters representing a candidate cryptographic key;
• adjusting the parameters of the tensor network;
• generating a new candidate key sample and obtaining a candidate ciphertext obtained with the candidate cryptographic key;
• calculating a cost function with respect to a target ciphertext;
• measuring an overlap between the target ciphertext and the candidate ciphertext;
• determining whether the overlap has reached a threshold value is reached;
• and
• if threshold value is not reached, repeating the method by further adjusting the parameters of the tensor network, if the threshold value is reached, determining that the candidate cryptographic key is the cryptographic key.