Is an ECPrivateKey stored in transient memory automatically in javacard, or do you have to specify (and how would you do that)?

by

Summary

A JavaCard appletTurkish an EC private key in persistent memory by default during key pair generation, exposing it to cold-boot attacks and unintended retention. This postmortem reveals how to correctly secure sensitive keys in transient RAM and why this oversight poses critical security risks.

Root Cause

  • Default memory allocation: JavaCard’s KeyBuilder creates keys in persistent memory (EEPROM/Flash) by default.
  • Missing transient flag: Developers fail to explicitly request volatile storage using KeyBuilder.TYPE_PRIVATE_TRANSIENT_RESET.
  • Lifecycle assumptions: Engineers incorrectly assume high-sensitivity keys are ephemeral by design, but JavaCard requires explicit configuration.

Why This Happens in Real Systems

  • JavaCard API prioritizes persistence for keys to survive reboots, aligning with stored credentials like payment certificates.
  • Transient memory allocation isn’t the default because:
    • Cards historically lacked secure RAM cleanup mechanisms
    • Persistent storage simulates “permanent” cryptographic identity
  • Documentation emphasizes domain parameter initialization over memory-safety nuances.

Real-World Impact

  • Cold-boot attacks: Private keys retained in persistent memory can be extracted via physical tampering or side-channel attacks after card removal.
  • Wear-out: Repeated EEPROM writes (from key generation) degrade memory sectors prematurely.
  • Security certifications: Fails FIPS/Common Criteria requirements for key zeroization after userofiler resolutionCryptography

Example or Code

// CORRECT: Force transient storage using KeyBuilder flags
KeyPair keyPair = new KeyPair(
    KeyPair.ALG_EC_FP,
    KeyBuilder.LENGTH_EC_FP_256 | KeyBuilder.TYPE_PRIVATE_TRANSIENT_RESET // Critical flag
);

pubKey = (ECPublicKey)keyPair.getPublic();
privKey = (ECPrivateKey)keyPair.getPrivate();

// Initialize curves BEFORE generation
initialiseDomainParameters(pubKey);
initialiseDomainParameters(privKey);
keyPair.genKeyPair(); // Private key now resides in volatile RAM

How Senior Engineers Fix It

  1. Always combine flags: Use KeyBuilder.LENGTH_* | KeyBuilder.TYPE_PRIVATE_TRANSIENT_RESET when allocating private keys.
  2. Validate memory type: Verify key transient status post-creation with privKey.isTransient().
  3. Zeroize explicitly: Call privKey.clearKey() immediately after use even for transient keysdefense-in-depth.
  4. Bound key usage: Restrict operations to cryptographicecia
  5. Test memory wipe: Power-cycle the card and confirm key destruction via error handling.

Why Juniors Miss It

  • API unfamiliarity: KeyBuilder flags documentation lacks emphasis on memory implications.
  • Misplaced focus: Over-prioritizing curve parameter setup while neglecting storage attributes.
  • Lab-environment bias: Testing on simulators that ignore memory persistence nuances.
  • False assumption: Believing “private” implies automatic volatility despite JavaCard’s persistent-by-default rule.
  • Legacy code mimicry: Copying non-secure examplesang.