Implement file encryption and security features

[b0ase]

Description

Add end-to-end encryption and comprehensive security features.

Tasks

• Implement client-side AES-256 encryption
• Create key derivation from user credentials
• Add file integrity verification with SHA-256
• Implement secure key storage with HandCash
• Add file access control lists (ACLs)
• Create sharing with encryption keys
• Implement zero-knowledge proofs for privacy
• Add security audit logging
• Create penetration testing suite

References

• PRD Section 7: Security Requirements
• End-to-end encryption mentioned

Priority: High