# Secure Cryptographic Key Encapsulation and Recovery Scheme in Noisy Network Conditions
## 4 CRP Mechanism
###### Operating a terminal device in noisy networks  
Before releasing the terminal device (a rover, a drone, some other kind of robot, etc.) in the noisy network, a fixed set of encrypted commands are downloaded during what is called the enrollment cycle, which is described below. The commands can be anything that is appropriate to the application, like a set of navigational waypoints, a simple directional movement, or anything else of arbitrary complexity. The command files can be encrypted with a symmetric cipher, each with its own separate key. Only the cipher texts are saved onto the terminal device, while the plain texts and keys are kept in the server driving the device. The CRP mechanism needed to encapsulate these keys with a subset of responses, as presented in Section 5, is directly based on the encrypted commands. During the initial key encapsulation cycle, which is done during enrollment, the system hashes each encrypted command (that is, it hashes the cipher text) using the extended output Secure Hash Algorithms; SHA3-256 cryptographic hash function. A password that is shared between the two devices produces sets of challenges, which the system uses to query the hash digests of the cipher texts and from those queries produce sets of responses. Finally, for each set of responses, the key used to encrypt the associated command data produces a subset of responses, where the responses that are kept correspond to the set positions of the key. Responses corresponding to unset key positions are discarded, along with the key once the process is completed. The terminal device loaded with the encrypted command data and the shared password, which go out into the field is deployed.When the device operator wishes to issue a  
Figure 1: Challenge response pair mechanism for authentication. The user requests to verify itself. The server, having access to the same crypto table, issues a challenge, and the user utilizes the crypto table to generate a response unique to that challenge. The server can verify the user’s authenticity by generating the corresponding response on its own and comparing it with the received one. particular command to the terminal device, they transmit the response subset associated with the required command. This transmission can be corrupted in transit; alone, this transmission can tolerate up to 40% noise. Combined with additional ECCs that we discuss, we expect that this technology can exchange bit-perfect keys at staggering levels of corruption. To recover the command, the terminal device receives a corrupted response subset. The device uses its shared password, the cipher text of the command file, and the same CRP mechanism to produce a full set of responses from the cipher text; this response set will be a pristine version of the responses computed during enrollment. The device then runs the matching algorithm described in Section 5, matching the full set of responses with their received subset, thereby reconstructing the set and unset bit positions and recovering the key despite the noise injected in the subset of responses. **Template-less key generation from biometric images:** An additional application involves the use of biometric images for the CRP mechanism. Each biometric image is used as a PUF, which represents an innovative framework within the realm of security technologies, leveraging distinctive and inherent physical traits of individuals to construct resilient and non-replicable digital identifiers. As opposed to conventional security systems that preserve sensitive data in centralized databases, such as passwords, fingerprints, or facial features, the idea of using biometric PUFs to generate keys without storing facial information is an exciting concept. This innovative methodology not only mitigates the vulnerabilities associated with the centralized storage of biometric information but also augments overall security.