AWS CloudHSM

Overview 

• Hardware Security Module in the cloud
• Separation of duties
  • AWS operates device but does not have access to key material
  • Customer has access the key material
• Certified by 3rd parties (e.g. government agencies)
• Multiple devices
  • HSM device may be deployed on-premise (e.g. backup HSM)
• Integrated with CloudTrail
• In 2017/08 new release (old is now CloudHSM Classic)
  • Easier provisioning
  • Different pricing model (no up-front cost)
  • Higher certification (compliance)

Use Cases

• Oracle Transparent Data Encryption (TDE)
• SSL Offloading
  • e.g. Apache offloads SSL operations to HSM
• Storing keys for Certificate Authority
• Regulatory or contractual requirements

HSM

• Physical device
  • Storage of key material
    • Key material never leaves the device
  • Crypto operations (e.g. encrypt/sign)
• Single tenant (dedicated)
• Tamper detection (key material is wiped out)
• Lives in dedicated CloudHSM VPC
  • Has Elastic Network Interface associated
    • located in customer VPC (not AWS-owned CloudHSM VPC)
    • same AZ

HSM User

• Most operations require authentication
• User Types
  • Precrypto Officer (PRECO) - temporary (default password). Becomes CO
  • Crytpto Office (CO) - user management (control plane)
  • Crypto User (CU) - key management + crypto operations (data plane)
  • Appliance User (AU) - cloning, synchronization (used by AWS)
• Quorum Authentication (M of N)
  • 2 or more HSM users required to perform an operation

Cluster

• Collection of HSM devices (1-28)
• Use cases
  • High Availability
  • Throughput (load balancing)
• Keys are synchronized between devices
• Initialization
  • Retrieve CSR
  • Create private key 
  • Sing CSR

Client

• CloudHSM Client
  • Mutual authentication (client <-> HSM)
    • Certificate based
  • Runs on any instance that can connect to HSM ENI
    • Not only EC2
  • Lives in different VPC than HSM
  • All other consumers go through that client
• Protocols
  • Java JCA/JCE (Java Cryptography Architecture/Java Cryptography Extensions)
  • PKCS#11 (programming interface)

Backup

• Natively supported
• Scheduled/on-demand
• Restore to cluster
• Backed-up
  • Key material
  • Users
  • Configurations
• Stored in Bucket (AWS owned)
  • Encrypted based on embedded key

HSM vs. KMS

• HSM total control but requires management (e.g. access control)
• KMS designed for the cloud (scalability, durability, performance) - easier to use
  
  • Integrated with other services
  • Access controlled through policy
  • Allows envelope encryption
  • Easier key-rotation: enough to re-encrypt the data key - not entire data set

HSM vs. TPM

• TPM is a chip on motherboard (often on laptops)
  • Used for disk encryption as "root of trust"
    • Integrity authentication for boot process
  • Includes unique RSA key burnt into it
• HSM is added as external device
  • Smaller devices can be put on corporate ID badge
  • performs sign/encrypt on the device

Key Hierarchy approach to encryption

• Single Master Key used to encrypt Data Key
• Encrypted Data Key stored along with ciphertext
• Benefits
  • Easier to protect single (master) key, e.g. KMS/HSM
  • Segmentation of data that is protected (different data keys)

References

• http://security.stackexchange.com/questions/88744/what-are-the-differences-between-tpm-and-hsm
• https://docs.aws.amazon.com/cloudhsm/latest/userguide/hsm-users.html