# Siberia: A Self-Sovereign Identity and Multi-Factor Authentication Framework for Industrial Access
## 2 Materials and Methods
### Secure SASV Module  
The overall architecture of the secure SASV module implemented in SIBERIA is shown in Figure 3. It comprises two independent components interacting with the SSI module: (1) the Keys Manager, responsible for the generation and management of keys used in the HE of voiceprints, and (2) the biometric processor, which handles voiceprint generation and the identity verification of the holder. These two components are deployed on separate servers to enhance security and privacy, ensuring that the private keys required for decryption are stored independently from the encrypted voiceprints. The process of biometric authentication, considering the SIBERIA SASV module, consists of five steps, detailed as follows:  
* The issuer in the SSI module sends a request to the Keys Manager to generate a set of cryptographic keys for secure SASV processing.
* The Keys Manager returns the set of public and cryptographic keys to the holder. The private key is securely retained by the Keys Manager and is later used to decrypt the biometric scores.
* During enrollment, the issuer submits an audio sample from the holder along with the public key to the biometric processor, which generates the encrypted voiceprint that is stored in a voice VC. During authentication, the verifier provides a verification audio sample from the holder, the encrypted enrollment voiceprint stored within the VC, and the set of public, Galois, and relin keys. These are used to perform identity verification entirely within the HE domain.
* The biometric processor returns either the encrypted voiceprint to the issuer during the enrollment phase or a pair of encrypted biometric and anti-spoofing scores during authentication of the holder's identity.
* The pair of biometric and anti-spoofing scores is sent by the SSI verifier to the Keys Manager, which decrypts them and performs a score-level fusion to produce the final SASV authentication score.  
Figure 2: High-level architecture of the SIBERIA SSI module.  
Finally, the SASV score is sent back to the SSI verifier, where it is evaluated against a predefined threshold to determine whether the identity should be accepted or rejected.  
To preserve the holder's privacy and adhere to SSI principles, no identifiable information is stored on either the Keys Manager or the biometric processing servers. The encrypted voiceprint is stored locally on the holder's digital wallet, ensuring that biometric data remains under the holder's control. The Keys Manager retains a copy of the cryptographic keys, which are required for encrypting voiceprints and decrypting the biometric and anti-spoofing scores. The public keys are made accessible to the holder through authenticated API calls to the Keys Manager. The biometric module is stateless with respect to the holder. It does not retain any personal or biometric information. All data required for enrollment or authentication are transmitted through secure API requests initiated by the SSI module.  
The following subsections describe each of the individual components included in both the Keys Manager and the biometric authentication module.