hash verification

Hash Verification

Overview

Every file operation in CyberPatchMaker is protected by SHA-256 hashing at three verification points.

Verification Points

1. Pre-Verification (Source Version)

Before any changes, the applier verifies:

• Key file exists and its SHA-256 matches the expected source hash
• All required files exist and match their expected hashes
• If ANY mismatch is found, patch is rejected, no backup created, no changes made

2. During Operations

• Modify: Old file checksum verified before applying replacement, new file checksum verified after write
• Add: Written file checksum verified against expected hash
• Delete: File verified to exist with correct checksum before deletion

3. Post-Verification (Target Version)

After all operations, verifies:

• Key file hash matches target version
• All modified and added files match expected target hashes
• If verification fails: automatic rollback from backup restores original state

Note: Delete, delete-directory, and add-directory operations are not re-verified post-patch (no meaningful checksum to verify).

Implementation

// pkg/utils/checksum.go
func CalculateFileChecksum(filePath string) (string, error)  // SHA-256 of file
func CalculateDataChecksum(data []byte) string              // SHA-256 of bytes
func VerifyFileChecksum(filePath, expectedChecksum string) (bool, error)  // compare

// Streaming: io.Copy into sha256.New() for memory-efficient hashing

Parallel checksum computation is handled by scanner.ScanDirectoryParallel() using a worker pool.

Failure Example

Pre-verification failed: key file checksum mismatch
Expected: abc123...
Got:      xyz789...
This patch requires version 1.0.0
Your installation may be corrupted or modified

Security Properties

• Collision resistance: Finding two files with same SHA-256 is computationally infeasible
• Pre-image resistance: Cannot create a file that matches a specific hash
• Tamper evidence: Any byte change produces a completely different hash
• Checksum verification in the self-contained EXE header prevents patch data tampering