Salted hashing method for response-based cryptography

A method of generating one or more cryptographic keys at a server device, the server device having a database of previously measured physical characteristics of physical-unclonable-function (“PUF”) devices of an addressable array of PUF devices on a client device, comprising:

• at the server device,
• generating a set of instructions including PUF challenges identifying a range of PUF devices in the addressable array of PUF devices;
• transmitting the set of instructions to the client device;
• retrieving, from the database, previously measured physical characteristics of PUF devices identified by the set of instructions, and generating therefrom a first seed;
• computing a first cryptographic hash from the first seed;
• receiving, from the client device, a second cryptographic hash of a response bitstream generated by, in response to the transmitted set of instructions, measuring physical characteristics of PUF devices of the addressable array of PUF devices identified in the instructions;
• comparing the first and second cryptographic hash;
• if the first and second cryptographic hashes do not match, iteratively modifying the first seed to create a modified first seed, hashing the modified first seed to create a hashed modified first seed, and comparing the hashed modified first seed to the second cryptographic hash until the hashed modified first seed matches the second cryptographic hash, or a predetermined timeout threshold is crossed, and
• when the first cryptographic hash or the hashed modified first seed match the second cryptographic hashes, salting the first seed to create a salted first seed, in accordance with a predetermined salting algorithm and generating one or more cryptographic keys from the salted first seed using a predetermined cryptographic key generation algorithm.

A method of cryptographic communication between a client device having a physical-unclonable-function (“PUF”) array of addressable PUF devices and a server device having a database of previously measured physical characteristics of PUF devices of the addressable array of PUF devices on the client device, comprising:

• at the server device,
• generating a set first of instructions including PUF challenges identifying a first range of addressable PUF devices in the array of addressable PUF devices;
• transmitting the first set of instructions to the client device;
• retrieving, from the database, previously measured physical characteristics of the first range of PUF devices identified by the first set of instructions, and generating therefrom a first seed;
• computing a first cryptographic hash from the first seed;
• at the client device,
• receiving the first set of instructions including PUF challenges identifying the first range of devices in the PUF array;
• measuring a set of physical characteristics of the first range of PUF devices identified by the first instructions and generating a second seed from responses resulting from measurements of the set of physical characteristics;
• computing a cryptographic hash of the second seed, and transmitting the hash of the second seed to the server device;
• modifying the second seed according to a predetermined salting algorithm resulting in a salted second seed,
• generating one or more cryptographic keys with the salted second seed;
• at the server device,
• hashing the first seed resulting in a cryptographic hash of the first seed;
• comparing the cryptographic hash of the first seed to the cryptographic hash of the second seed, and if the cryptographic hash of the first seed matches the cryptographic hash of the second seed, modifying the first seed according to the predetermined salting algorithm resulting in a salted first seed, and generating one or more cryptographic keys with the first salted seed,
• wherein, at the server, if the cryptographic hash of the first seed and the cryptographic hash of the second seed do not match, iteratively modifying the first seed resulting in a modified first seed, hashing the modified first seed, and comparing a hash of the modified first seed to the cryptographic hash of the second seed until a hash of the modified first seed matches the cryptographic hash of the second seed, or a predetermined timeout threshold is crossed.