Process Authentication with HSM

TL;DR

This guide shows how to authenticate Windows or Linux processes using a Hardware Security Module (HSM). This adds strong security by tying process execution to a trusted hardware device, preventing tampering and unauthorized access. We’ll cover key concepts, setup steps for both operating systems, and basic code examples.

Understanding the Concepts

An HSM is a dedicated cryptographic processor designed to protect sensitive keys and perform cryptographic operations securely. Process authentication with an HSM typically involves these steps:

• Key Generation: A unique key pair is generated within the HSM. The private key never leaves the HSM.
• Signing: Before a process runs, it requests a signature from the HSM using its private key. This signature proves the process’s identity and integrity.
• Verification: A trusted component verifies the signature against the corresponding public key (which can be distributed safely). If verification succeeds, the process is allowed to run; otherwise, it’s blocked.

Windows Setup

1. HSM Driver Installation: Install the driver provided by your HSM vendor. This allows Windows to communicate with the device. Ensure the driver is compatible with your Windows version.
2. CryptoAPI Configuration: Configure CryptoAPI (Cryptographic Application Programming Interface) to use the HSM as a cryptographic service provider (CSP). You might need to add the HSM to the list of available CSPs in certmgr.msc.
3. Key Generation using CryptoAPI: Use CryptoAPI functions (e.g., CryptGenKey) to generate a key pair within the HSM. Specify the appropriate key algorithm and key length.

   HCRYPTPROV hProv = NULL;
   if (!CryptAcquireContext(&hProv, NULL, MS_ENHANCED_PROV, PROV_RSA_HSM, CRYPT_VERIFYCONTEXT))
   {
       // Handle error
   }
   

4. Process Signing: Implement a signing mechanism. Before the process starts:
   • Hash the process executable file.
   • Use CryptoAPI to sign the hash with the HSM’s private key.
5. Signature Verification: Create a trusted component (e.g., a kernel driver or a secure bootloader) that verifies the signature before allowing the process to run. Use CryptoAPI functions (e.g., CryptVerifySignature) for verification.

   if (CryptVerifySignature(hHash, NULL, hSigBlob, dwSigLen, phKey))
   {
       // Signature is valid
   }
   

Linux Setup

1. PKCS#11 Library Installation: Install the PKCS#11 library provided by your HSM vendor. This provides a standard interface for interacting with the HSM.
2. HSM Configuration: Configure the PKCS#11 library to connect to your HSM. This usually involves specifying the path to the library file and any required PINs or authentication credentials.
3. Key Generation using PKCS#11: Use the PKCS#11 API (e.g., C_GenerateKey) to generate a key pair within the HSM.

   CK_RV rv = C_GenerateKey(hSession, &keyGenTemplate);
   if (rv != CKR_OK)
   {
       // Handle error
   }
   

4. Process Signing: Implement a signing mechanism. Before the process starts:
   • Hash the process executable file using a secure hashing algorithm (e.g., SHA-256).
   • Use PKCS#11 functions to sign the hash with the HSM’s private key.
5. Signature Verification: Create a trusted component (e.g., using systemd or a custom init script) that verifies the signature before allowing the process to run. Use PKCS#11 functions (e.g., C_Verify) for verification.

   CK_RV rv = C_Verify(hSession, hKey, hash, dwHashLen);
   if (rv != CKR_OK)
   {
       // Signature is invalid
   }
   

Important Considerations

• Secure Boot: Integrate the public key into a secure boot process to ensure that only signed processes can run.
• Tamper Detection: Implement mechanisms to detect if the process executable has been modified after signing.
• Key Management: Securely manage the HSM keys, including backups and access control.
• Auditing: Log all key usage events for auditing purposes.