Smart Card Cryptography

Smart Card Cryptography

Modern smart cards carry a dedicated crypto coprocessor that executes symmetric and asymmetric cryptographic operations in hardware, at speeds orders of magnitude faster than the card's general-purpose CPU and without exposing intermediate values to the main bus. Understanding which algorithms a card supports — and their performance trade-offs — is essential before selecting a card platform.

Use the EAL Comparator to cross-reference algorithm support against Common Criteria certification level for specific card families.

Asymmetric Algorithms — RSA and ECC

Asymmetric cryptography on smart cards serves key generation, digital signatures, and key agreement. The two dominant families are RSARSACryptographyPublic-key algorithm for smart card signatures and key exchange.Click to view → and Elliptic Curve Cryptography (ECCECCCryptographyEfficient public-key cryptography using elliptic curves.Click to view →).

ECC at 256 bits provides the same security margin as RSA-3072 with significantly smaller key sizes and faster operations — an important consideration for secure element deployments where memory and latency budgets are tight.

Symmetric Algorithms — AES and Legacy

Secure element platforms support AESAESCryptographyNIST symmetric block cipher for smart card encryption.Click to view → natively via the crypto coprocessor. AES-128 is used in SCP03 secure channels, AES-256 in high-assurance key storage and wrapping, and 3DES3DESCryptographyLegacy triple-DES symmetric cipher in payment smart cards.Click to view → is retained only for legacy EMVEMVApplicationGlobal chip payment card standard.Click to view → and SCP02 backward compatibility.

AES-GCM provides authenticated encryption with associated data (AEAD) and is preferred for in-applet secure messagingsecure messagingProtocolCryptographic protection of APDUAPDUProtocolCommunication unit between card and reader.Click to view → command/response pairs.Click to view →. Cards claiming Common Criteria EAL4+ must implement at least AES-128 in all modes required by their protection profile.

Crypto Coprocessor Architecture

The crypto coprocessor is a hardware accelerator physically isolated from the card's CPU address space. Key material passes to the coprocessor through a dedicated key-loading interface; the CPU never has read access to the key registers.

Internally the coprocessor contains:

• Arithmetic logic unit — for modular exponentiation (RSA), scalar multiplication (ECC)
• Key registers — volatile (session) and non-volatile (persistent) storage
• TRNG — True Random Number Generator, typically based on thermal noise sampling
• AES engine — pipelined S-box and key schedule hardware
• DES engine — legacy Feistel hardware for 3DES backward compatibility
• Hash engine — SHASHACryptographyNIST hash functions for smart card integrity and signatures.Click to view →-1 / SHA-256 / SHA-384 / SHA-512 hardware acceleration

Key Hierarchy and Derivation

Keys on a smart card exist in a hierarchy that limits blast radius if a single key is compromised. The root is typically held in a certified HSM at the card management back-end; the card holds only derived or card-unique keys.

Master Key (HSM)
└── Issuer Key (per-batch)
    └── Card Key (per-card, derived from serial number)
        ├── Authentication Key
        ├── Encryption Key (session key wrapped by Card Key)
        └── Applet Key (per-application)

Key derivation uses NIST SP 800-108 counter-mode KDF or EMV-style diversification. The GlobalPlatform specification governs how card-unique keys are structured for SCP03SCP03SoftwareAES-based secure channel protocol.Click to view → sessions. See Key Management for Smart Cards for the complete operational model.

Post-Quantum Readiness

NIST finalised ML-KEM (CRYSTALS-Kyber) and ML-DSA (CRYSTALS-Dilithium) in FIPS 203/204 (2024). Newer secure element platforms are beginning to add post-quantum coprocessors, though embedded memory and power constraints make lattice-based algorithms significantly heavier than ECC on current card silicon. For deployments with 10+ year credential lifetimes, request PQC roadmap documentation from the card vendor.

See Common Criteria for Smart Cards for how algorithm support is verified in formal security evaluations.