Windows Catalog (CAT) File Format

Overview

Windows Catalog (CAT) files are cryptographic catalog files used by Microsoft Windows to store digital signatures and security information for groups of files. They serve as a central repository for digital signatures, allowing the operating system to verify the authenticity and integrity of system files, drivers, and applications without embedding signatures directly in each file.

Technical Details

File Extension: .cat
MIME Type: application/vnd.ms-pki.seccat
Format Type: PKCS#7 Cryptographic Message
Digital Signature: Authenticode-based
Hash Algorithms: MD5, SHA-1, SHA-256, SHA-512
Platform: Windows NT family

CAT files contain:

• Digital signatures for file collections
• Hash values of cataloged files
• Certificate chains and trust information
• Timestamp information
• File attribute data

Key Features

• Centralized Signing: Single signature file for multiple files
• Integrity Verification: Detects file tampering or corruption
• Trust Validation: Verifies publisher authenticity
• Performance Optimization: Faster signature verification
• Scalability: Efficient for large file collections
• Timestamp Support: Allows signature validation beyond certificate expiry

File Structure

CAT File Structure (PKCS#7):
├── Content Info
├── Signed Data
│   ├── Version
│   ├── Digest Algorithms
│   ├── Content Info
│   │   ├── Content Type (SPC_CAT_OBJID)
│   │   └── Content (Catalog Data)
│   │       ├── Catalog Header
│   │       ├── Catalog Entries
│   │       │   ├── File Hash
│   │       │   ├── File Attributes
│   │       │   └── Member Info
│   │       └── Catalog Attributes
│   ├── Certificates
│   └── Signer Info
│       ├── Version
│       ├── Issuer and Serial Number
│       ├── Digest Algorithm
│       ├── Authenticated Attributes
│       ├── Signature Algorithm
│       └── Signature

Common Use Cases

1. Driver Signing: Hardware driver package validation
2. System File Protection: Windows system file integrity
3. Software Distribution: Application package validation
4. Update Packages: Windows Update file verification
5. Enterprise Deployment: Corporate software validation
6. Security Compliance: Meeting digital signature requirements

Windows Integration

System File Protection

Windows uses CAT files for:
├── %SystemRoot%\system32\catroot\
├── %SystemRoot%\system32\catroot2\
├── %SystemRoot%\system32\DriverStore\
└── %SystemRoot%\inf\

Driver Store Integration

Driver Package Structure:
├── mydriver.sys
├── mydriver.inf
├── mydriver.cat  (Contains signatures for all files)
└── mydriver.txt

Command Line Tools

Windows SDK Tools

REM Create catalog file
makecat -v catalog.cdf

REM Sign catalog file
signtool sign /f certificate.pfx /p password catalog.cat

REM Verify catalog signature
signtool verify /v /cat catalog.cat file.sys

REM Display catalog contents
signtool catdb /v catalog.cat

Catalog Definition File (CDF)

[CatalogHeader]
Name=MyCatalog.cat
ResultDir=.\
PublicVersion=0x0000001
EncodingType=0x00010001
CATATTR1=0x10010001:OSAttr:2:6.0

[CatalogFiles]
<hash>file1.sys=file1.sys
<hash>file2.dll=file2.dll
<hash>file3.exe=file3.exe

PowerShell Integration

# Get catalog information
Get-AuthenticodeSignature "C:\Windows\system32\catroot\{GUID}\catalog.cat"

# Verify file against catalog
$catalog = "C:\path\to\catalog.cat"
$file = "C:\path\to\file.sys"
Test-FileCatalog -CatalogFilePath $catalog -FilePath $file

# Create new catalog
New-FileCatalog -Path "C:\source\files" -CatalogFilePath "output.cat"

Programming APIs

Windows Cryptography API

#include <windows.h>
#include <wintrust.h>
#include <mscat.h>

// Verify file against catalog
BOOL VerifyFileWithCatalog(LPCTSTR filePath, LPCTSTR catalogPath) {
    HANDLE hCatalog = CryptCATOpen((PWSTR)catalogPath, 
                                   CRYPTCAT_OPEN_EXISTING, 
                                   NULL, 0, 0);
    if (hCatalog == INVALID_HANDLE_VALUE) return FALSE;
    
    // Calculate file hash
    HANDLE hFile = CreateFile(filePath, GENERIC_READ, FILE_SHARE_READ,
                              NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    
    DWORD hashSize = 0;
    BYTE* hashData = NULL;
    
    if (CryptCATCalculateHash(hFile, &hashSize, &hashData)) {
        // Find hash in catalog
        CRYPTCATMEMBER* pMember = CryptCATFindMemberByHash(hCatalog, hashData, hashSize);
        
        if (pMember) {
            // Verify signature
            CATALOG_INFO catInfo = {0};
            catInfo.cbStruct = sizeof(CATALOG_INFO);
            catInfo.pwszCatalogFile = (PWSTR)catalogPath;
            
            WINTRUST_CATALOG_INFO wtci = {0};
            wtci.cbStruct = sizeof(WINTRUST_CATALOG_INFO);
            wtci.dwCatalogVersion = 0;
            wtci.pcwszCatalogFilePath = catalogPath;
            wtci.pcwszMemberTag = pMember->pwszReferenceTag;
            wtci.pcwszMemberFilePath = filePath;
            
            WINTRUST_DATA wd = {0};
            wd.cbStruct = sizeof(WINTRUST_DATA);
            wd.dwUIChoice = WTD_UI_NONE;
            wd.fdwRevocationChecks = WTD_REVOKE_NONE;
            wd.dwUnionChoice = WTD_CHOICE_CATALOG;
            wd.pCatalog = &wtci;
            
            GUID action = WINTRUST_ACTION_GENERIC_VERIFY_V2;
            LONG result = WinVerifyTrust(NULL, &action, &wd);
            
            free(hashData);
            CryptCATClose(hCatalog);
            CloseHandle(hFile);
            
            return (result == ERROR_SUCCESS);
        }
    }
    
    CryptCATClose(hCatalog);
    CloseHandle(hFile);
    return FALSE;
}

.NET Framework

using System.Security.Cryptography.X509Certificates;
using System.Security.Cryptography.Pkcs;

public class CatalogValidator
{
    public bool VerifyFileInCatalog(string filePath, string catalogPath)
    {
        try
        {
            // Read catalog file
            byte[] catalogData = File.ReadAllBytes(catalogPath);
            
            // Parse PKCS#7 signed data
            SignedCms signedCms = new SignedCms();
            signedCms.Decode(catalogData);
            
            // Verify signature
            signedCms.CheckSignature(true);
            
            // Calculate file hash
            byte[] fileHash = CalculateFileHash(filePath);
            
            // Check if hash exists in catalog
            return CheckHashInCatalog(signedCms.ContentInfo.Content, fileHash);
        }
        catch
        {
            return false;
        }
    }
    
    private byte[] CalculateFileHash(string filePath)
    {
        using (var sha256 = SHA256.Create())
        using (var stream = File.OpenRead(filePath))
        {
            return sha256.ComputeHash(stream);
        }
    }
    
    private bool CheckHashInCatalog(byte[] catalogContent, byte[] fileHash)
    {
        // Parse catalog content to find matching hash
        // Implementation depends on catalog structure
        return true; // Placeholder
    }
}

Driver Package Signing

INF2CAT Tool

REM Create catalog for driver package
inf2cat /driver:C:\MyDriver /os:10_X64,10_X86

REM Sign the generated catalog
signtool sign /v /s "My Store" /n "My Certificate" /t http://timestamp.url mydriver.cat

REM Verify the signed catalog
signtool verify /v /cat mydriver.cat mydriver.sys

Driver Package Structure

MyDriver/
├── mydriver.inf     (Driver information file)
├── mydriver.sys     (Driver binary)
├── mydriver.cat     (Generated catalog)
├── coinstaller.dll  (Optional coinstaller)
└── readme.txt       (Documentation)

Security and Trust

Certificate Requirements

For CAT file signing:
├── Code Signing Certificate
├── Extended Validation (EV) for kernel drivers
├── Microsoft Hardware Certification (WHQL)
└── Cross-signing for older Windows versions

Trust Verification Process

// Comprehensive trust verification
BOOL VerifyCompleteTrust(LPCTSTR catalogPath, LPCTSTR filePath) {
    // 1. Verify catalog signature
    if (!VerifyCatalogSignature(catalogPath)) return FALSE;
    
    // 2. Check certificate chain
    if (!VerifyCertificateChain(catalogPath)) return FALSE;
    
    // 3. Verify file hash in catalog
    if (!VerifyFileHashInCatalog(catalogPath, filePath)) return FALSE;
    
    // 4. Check timestamp validity
    if (!VerifyTimestamp(catalogPath)) return FALSE;
    
    return TRUE;
}

Enterprise Deployment

Group Policy Integration

Computer Configuration\
  Windows Settings\
    Security Settings\
      Software Restriction Policies\
        Certificate Rules\
          (Add catalog certificate)

Custom Catalog Deployment

# Deploy custom catalog to enterprise
$catalogPath = "\\server\share\enterprise.cat"
$targetPath = "$env:SystemRoot\system32\CatRoot\{GUID}"

# Copy and register catalog
Copy-Item $catalogPath $targetPath
& certlm.msc # Import certificate if needed

# Verify deployment
Get-ChildItem $targetPath -Filter "*.cat" | 
    ForEach-Object { signtool verify /v $_.FullName }

Performance Considerations

Catalog Size Optimization

Optimization Strategies:
├── Limit files per catalog (recommended: <10,000)
├── Use appropriate hash algorithms (SHA-256 preferred)
├── Optimize certificate chain length
└── Minimize catalog attributes

Verification Performance

// Optimized verification with caching
class CatalogCache {
private:
    std::unordered_map<std::string, bool> verificationCache;
    
public:
    bool VerifyWithCache(const std::string& filePath, 
                        const std::string& catalogPath) {
        std::string key = filePath + "|" + catalogPath;
        
        auto it = verificationCache.find(key);
        if (it != verificationCache.end()) {
            return it->second;
        }
        
        bool result = VerifyFileWithCatalog(filePath.c_str(), 
                                           catalogPath.c_str());
        verificationCache[key] = result;
        return result;
    }
};

Troubleshooting

Common Issues

REM Catalog signature verification failed
signtool verify /v /pa catalog.cat

REM Check Windows trust settings
certlm.msc

REM Rebuild catalog database
sfc /scannow

REM Clear catalog cache
del /q %SystemRoot%\system32\catroot2\*

Debugging Tools

REM View catalog contents
signtool catdb /v catalog.cat

REM Check file hash
certutil -hashfile file.sys SHA256

REM Verify against specific catalog
signtool verify /v /cat catalog.cat file.sys /pa

Windows Catalog files provide a robust and efficient mechanism for maintaining the security and integrity of the Windows ecosystem, enabling scalable digital signature verification while supporting the platform's security architecture.