Hardware Security Module

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A Hardware Security Module (often abbreviated to HSM, also often called a Host Security Module) is a plug-in card (PCI) or external device (RS232/SCSI/IP/USB/PCMCIA) for a general purpose computer and may even be an embedded system itself.

The job of the HSM is to securely generate and/or store long term secrets for use in cryptography and physically protect the access to and use of those secrets over time. Generally these are private keys used in Public-key cryptography; some HSMs also allow for hardware protection of symmetric keys.

Many HSM systems have a means to securely backup the keys either in a wrapped form via the computer's operating system or externally using a smartcard or some other USB token. The most robust HSM systems are those when secrets are not exported even when migrating between HSMs or performing backup operations.

Most HSM systems are also hardware cryptographic accelerators. Since they do not allow the keys to be removed from the device in an unencrypted form, they must be able to perform the common cryptographic operations, as a happy consequence these HSMs will accelerate the intense maths (especially the case in Public-key cryptography) and provide better performance than a completely software based crypto system.

It is important to note that keys protected by HSM are only truly 'hardware protected' if they were generated inside the hardware itself, importing a standard software protected key into an HSM will still mean that a non-hardware protected copy of the key material might still exist on old backups.

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[edit] Tamper Resistance

The physical security of the HSM is usually assigned as a level of the FIPS 140-2 validation, being FIPS 140-2 Level 3 and the recent FIPS 140-2 Level 4 the ones preferred by customers, since they assure high physical security.

[edit] HSM Software APIs

Ingrian Networks, RSA, Sun/IBM Java, Microsoft, Mozilla Foundation and OpenSSL all provide or implement API level hooks that allow software to make use of a HSM. Below is a list of popular cryptography APIs that can be used with hardware modules from different vendors.

  • PKCS#11 - RSA's API, designed to be platform independent, defining a generic interface to HSMs. Also known as 'cryptoki'
  • JCE/JCA - Java's Cryptography API
  • Microsoft CAPI - Microsoft's API as used by IIS, CA and others, also available from .net

[edit] Card Payment System HSMs

Special HSMs are used in card processing systems, that do not use the PKCS#11 API. While there is no global standard on the low level API for "payment" HSMs, common principles are shared among HSM software developers.

There are two main groups of HSMs used here:

OEM or integrated modules for automated teller machines and POS terminals:

  • to encrypt the PIN entered when using the card.
  • to load keys into protected memory.

Authorisation and personalisation modules may be used to:

  • check an on-line PIN by comparing with an encrypted PIN block.
  • verify credit/debit card transactions by checking card security codes or by performing host processing component of an EMV based transaction
  • support a crypto-API with a Smart Card (such as an EMV).
  • re-encrypt a PIN block to send it to another authorisation host.
  • support a protocol of POS ATM network management.
  • support de-facto standards of host-host key|data exchange API.
  • generate and print a "PIN mailer".
  • generate data for a magnetic stripe card (PVV, CVV).
  • generate a card keyset and support the personalisation process for Smart Cards.

[edit] Organizations Manufacturing HSMs

  • Thales e-Security - HSM 8000, P3 Crypto Module, WebSentry, SafeSign Crypto Module
  • Utimaco - SafeGuard CryptoServer
  • xyzmo - xyzmo SIGNificant server

[edit] External links