What's the Technical Difference Between HSM and TPM

Introduction

Both Hardware Security Module (HSM) and Trusted Platform Module (TPM) are hardware devices used to provide cryptographic functions and key management capabilities in order to secure sensitive data, keys, applications and computer systems. However, there are some notable differences between the two technologies.

HSM refers to an external standalone appliance or add-on card that safeguards and manages digital keys or other sensitive cryptographic data. It protects critical security parameters such as cryptographic keys, passwords, certificates through hardened secure cryptoprocessors. HSMs enable a high degree of physical tamper resistance and provide crypto processing acceleration.

On the other hand, TPM is a dedicated microprocessor or chip embedded into the motherboard of a computer system to serve as its hardware-based root of trust. The TPM secure cryptoprocessor offers facilities to generate, store and limit the use of keys including encryption keys. It provides a set of capabilities to ensure platform integrity, platform authentication, and protects data via crypto functions.

While both HSM and TPM offer cryptographic functionality, there are significant technical differences between the two solutions in terms of design, security level, management, capabilities, use cases and compliance. Understanding the key differences helps to determine when to deploy a TPM vs HSM use case.

Key Differences Between HSM and TPM

Design and Form Factor

• HSM is designed as an external standalone network-connected appliance or PCI add-on card that is dedicated to provide crypto processing and key management. It is physically separated from the server systems.

• TPM is designed as an integrated chip directly embedded into the motherboard of a computer system. It is physically bound to the host system.

Level of Security

• HSM offers robust physical security through hardened tamper-resistant cryptomodules enclosed in tamper-evident enclosures. It actively detects and responds to tampering attempts.

• TPM offers relatively basic security through its embedded cryptoprocessor. It relies on the physical security of the computer system.

Cryptographic Capabilities

• HSM supports a wide range of cryptographic algorithms, key lengths and Functions like symmetric/asymmetric encryption/decryption, digital signatures, hash/message digest, MAC generation, true random number generation etc.

• TPM has limited crypto capabilities in terms of algorithms and functions. Mainly used for encryption/decryption, digital signatures, hash and random number generation.

Key Management and Storage

• HSM provides advanced key management capabilities including generating, importing, storing, backup, redundancy, and destroying keys in a secure vault.

• TPM has limited key management capabilities focused on securing keys related to the platform. Keys are generated and stored on the TPM chip.

Performance and Scalability

• HSM offers very high-performance crypto processing with thousands of operations per second and supports concurrent connections from multiple applications.

• TPM performance is much slower given its limited resource computer chip. It serves keys for one dedicated computer system.

Certificate Storage

• HSM can securely store X.509 certificates and perform functions like validating certificate paths.

• TPM has very limited certificate storage and lacks capabilities to validate certificate chains.

Supported Applications and Use Cases

• HSM can support a wide variety of applications like payment processing, PKI, identity and access management, TLS/SSL, code signing, database encryption etc.

• TPM use cases are mainly to secure platform authentication, disk encryption, DRM, integrity verification, and limited crypto functions.

Standards and Certifications

• HSM complies with stringent standards like FIPS 140-2 Level 3 or Level 4, Common Criteria EAL 4+ that validate its security claims.

• TPM follows TPM specifications published by Trusted Computing Group. It meets basic FIPS 140-2 Level 2 security in most cases.

Access Control and Authentication

• HSM provides extensive access controls backed by robust authentication mechanisms like smart cards, passphrases etc.

• TPM relies on access control mechanisms provided by the platform and OS. Uses weaker authentication via Platform Configuration Registers in some cases.

Backup and Redundancy

• HSM offers built-in redundancy and backup mechanisms to backup keys and restore them from tamper-proof backup.

• TPM does not provide any backup mechanisms for keys stored on the chips. Keys will be permanently lost if TPM is damaged or keys are deleted.

When to use Hardware Security Module (HSM)?

• Payment processing systems like EMV and credit card transactions
• Public Key Infrastructure (PKI) and certificate authority keys
• Critical database encryption keys
• Securing private keys for TLS/SSL and code signing
• Cryptographic keys for tokenization services
• Protecting credential issuance and identity management systems
• Key storage for Cryptocurrency wallets and exchanges
• High-value enterprise application and root encryption keys
• Use cases needing FIPS 140-2 Level 3 or higher security
• Applications requiring high-performance cryptography

When to use Trusted Platform Module (TPM)?

• Validating computer platform integrity
• Secure platform authentication
• Full disk encryption keys
• Digital rights management (DRM)
• Measured boot processes
• Integrity verification for early boot components
• Key protection for software-based BitLocker encryption
• Virtual TPM instances in virtualized environments
• Use cases with limited crypto performance needs

Conclusion

While HSM and TPM are both hardware secure cryptoprocessors, they are optimized for very different use cases. HSM offers robust security, versatile crypto functions, centralized key management, high performance, redundancy, and agility needed for business-critical applications with sensitive data. TPM provides basic embedded security keyed to one computer platform with focus on integrity measurements and platform authentication. Understanding their technical capabilities and differences allows organizations to determine the appropriate solution based on their specific requirements and use cases.

Related FAQs

1. Is HSM more secure than TPM?

Yes, HSM provides a far superior level of security compared to TPM. HSM offers robust physical tamper resistance and active anti-tampering protection of the cryptomodule. It also supports stringent standards like FIPS 140-2 Level 3/4 and Common Criteria EAL4+ certifications. TPM only provides basic embedded security relying on the physical computer system protections.

2. Can TPM be used instead of HSM?

TPM has very limited crypto capabilities, key management, and performance compared to dedicated HSM solutions. TPM is not a viable substitute for HSM in use cases like payment processing, PKI, enterprise database encryption, or high-value keys. TPM serves the niche use of securing platform-specific keys for a computer system.

3. Does TPM need separate driver support?

Yes, TPM requires a supporting driver called a TPM Device Driver to operate on the host system. The OS communicates with the TPM chip through this driver. HSM appliances work independently without need for any drivers.

4. Can HSM backup keys outside its boundaries?

HSM provides secure built-in backup mechanisms to optionally backup keys in an encrypted form to external secure media. However, the HSM vendor does not hold or have access to any keys outside the HSM boundary.

5. Is TPM vulnerable to physical attacks?

Yes, TPM being an embedded chip is susceptible to physical attacks like interception of bus communications, power analysis attacks, fault injection attacks, etc. HSM is more resilient against sophisticated physical attacks.

6. Does using TPM reduce need for trusted OS?

No, TPM relies on the OS and software for access control and authentication. HSM removes dependency on the OS and system software by providing secure embedded access controls isolated from rest of the system.

7. Can HSM be used for platform authentication or attestation?

While HSM is focused on cryptography, some models like SafeNet Luna HSM do provide support for platform attestation capabilities using measurements of HW/SW components extending TPM-based attestation.