48 Post Quantum Crypto for Dummies Don’t Lose Your Keys Secure storage for digital keys comes in many shapes and sizes. Smart cards are an example of secure storage that you carry on you every day, e.g., in your phone (SIM cards) or in your wallet (credit cards). These offer limited cryptographic functionality but nonetheless prevent usage of private information without proper authorization like the entry of your PIN. Other devices like TPMs and HSMs, which are more powerful, offer a broad range of cryptographic functionality. HSMs typically are plugin cards or network appliances that are deployed in data centers and are accessible over communication networks. We will look at TPMs and HSMs in more detail. TPMs A special kind of HSMs are Trusted Platform Modules (TPMs). These modules typically are bundled more closely with a specific device than HSMs. For example, dedicated TPMs can be soldered onto the main board of a system or logical TPMs can be implemented within a secure enclave of the processor. The TPM specification defines an API for the communication between the TPM and the host CPU. This API specifies the format of input and output buffers, commands, and cryptographic primitives that are implemented on the TPM. The TPM API has been defined with cryptographic agility in mind. However, the specific requirements of post-quantum cryptography will require changes to the current TPM implementations. For example, a future PQC-TPMwill need larger IO buffers for signatures and for importing and exporting public keys. A study on the impact of post-quantum cryptography on the TPM API can be found in https://www.sit.fraunhofer.de/ en/pqc-tpm/. HSMs Unlike TPMs, full-fledged HSMs offer the full gamut of cryptographic features. Cryptographic secrets are secured through a combination of dedicated hardware, secure storage, and certified firmware. Often, HSMs contain hardware support for key features like random number generation or hardware acceleration for cryptographic primitives. Additional properties, like physical tamper detection and an implementation of cryptographic functionality that is resistant to attacks using side-channel analysis, are essential to providing a protected environment with a strong security boundary. Digital keys are protected within that secure environment for their entire lifecycle: Secure keys are generated within the HSM and can be designated as secret or non-exportable. The former prevents access to the key material in plain text (while encrypted export of the key material is still permitted) whereas the latter
PQC_for_Dummies
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