Contract
- Input: data to protect, threat model, regulatory requirements.
- Output: cryptographic design + implementation checklist.
- Side effects: none (design only).
- Dependencies: none.
- Stop condition: design saved; anti-patterns identified; checklist complete.
- Risk: medium — weak cryptography has severe consequences.
- Boundary: designs cryptographic system; does not deploy unless explicitly executed.
Applied Cryptography
Apply cryptography correctly — encryption, signatures, key management, TLS — with implementation guidance and anti-pattern detection.
Process
1. Classify the data
- Sensitivity: public / internal / confidential / secret.
- Regulatory: GDPR (PII encryption), PCI-DSS (cardholder data), HIPAA (PHI), financial (PSD2), government (FIPS 140-2).
- At-rest vs in-transit vs in-use protection needed.
Completion criterion: data classification and protection requirements saved.
2. Choose primitives
- Encryption: AES-GCM (default), ChaCha20-Poly1305 (mobile / constrained), never ECB or unauthenticated CBC.
- Key exchange: X25519 (ECDH), RSA-KEM (hybrid).
- Signatures: Ed25519 (default), ECDSA (interoperability), RSA-PSS (legacy).
- Hashing: SHA-256 (SHA-3 as backup); Argon2id for passwords; BLAKE3 for fast hashing.
- MAC: HMAC-SHA256 (default); Poly1305 (with ChaCha20).
Completion criterion: primitives selected with justification.
3. Key management design
- Generation: cryptographically secure random number generator (CSPRNG); HSM for high-security keys.
- Storage: encrypted at rest; never hardcoded; use KMS (AWS KMS / GCP Cloud KMS / Azure Key Vault) or HSM.
- Rotation: automatic rotation schedule (e.g. annual for encryption keys; 90-day for session keys).
- Destruction: secure wipe when key expires.
Completion criterion: key management design saved.
4. TLS / PKI
- TLS 1.3 only (TLS 1.2 only if legacy requires; disable older versions).
- Cipher suite: only AEAD (AES-GCM, ChaCha20-Poly1305); disable RC4, 3DES, CBC.
- Certificate: issued by trusted CA; certificate chain validated; mutual TLS (mTLS) for service-to-service.
- HSTS header; OCSP stapling.
Completion criterion: TLS configuration documented.
5. Anti-pattern audit
Check for: hardcoded keys, password-based encryption (use KDF: Argon2id / scrypt), ECB mode, no MAC on encrypted data, IV reuse, missing key rotation, weak random, deprecated algorithms (MD5, SHA1 for signatures), lack of forward secrecy.
Completion criterion: anti-patterns listed; each fixed or documented with justification.
6. Deliver
Cryptographic design document + implementation checklist (key lengths, modes, rotation schedule) + anti-pattern corrections.
1---2name: sec-cryptography-applied3description: Apply cryptography — encryption at rest / in transit, digital signatures, key management, MACs, TLS/PKI, HSM, secure enclaves — with implementation guidance and anti-patterns.4---56## Contract78- **Input:** data to protect, threat model, regulatory requirements.9- **Output:** cryptographic design + implementation checklist.10- **Side effects:** none (design only).11- **Dependencies:** none.12- **Stop condition:** design saved; anti-patterns identified; checklist complete.13- **Risk:** medium — weak cryptography has severe consequences.14- **Boundary:** designs cryptographic system; does not deploy unless explicitly executed.1516# Applied Cryptography1718Apply **cryptography** correctly — encryption, signatures, key management, TLS — with implementation guidance and anti-pattern detection.1920## Process2122### 1. Classify the data23- Sensitivity: public / internal / confidential / secret.24- Regulatory: GDPR (PII encryption), PCI-DSS (cardholder data), HIPAA (PHI), financial (PSD2), government (FIPS 140-2).25- At-rest vs in-transit vs in-use protection needed.2627**Completion criterion:** data classification and protection requirements saved.2829### 2. Choose primitives30- **Encryption:** AES-GCM (default), ChaCha20-Poly1305 (mobile / constrained), never ECB or unauthenticated CBC.31- **Key exchange:** X25519 (ECDH), RSA-KEM (hybrid).32- **Signatures:** Ed25519 (default), ECDSA (interoperability), RSA-PSS (legacy).33- **Hashing:** SHA-256 (SHA-3 as backup); Argon2id for passwords; BLAKE3 for fast hashing.34- **MAC:** HMAC-SHA256 (default); Poly1305 (with ChaCha20).3536**Completion criterion:** primitives selected with justification.3738### 3. Key management design39- **Generation:** cryptographically secure random number generator (CSPRNG); HSM for high-security keys.40- **Storage:** encrypted at rest; never hardcoded; use KMS (AWS KMS / GCP Cloud KMS / Azure Key Vault) or HSM.41- **Rotation:** automatic rotation schedule (e.g. annual for encryption keys; 90-day for session keys).42- **Destruction:** secure wipe when key expires.4344**Completion criterion:** key management design saved.4546### 4. TLS / PKI47- TLS 1.3 only (TLS 1.2 only if legacy requires; disable older versions).48- Cipher suite: only AEAD (AES-GCM, ChaCha20-Poly1305); disable RC4, 3DES, CBC.49- Certificate: issued by trusted CA; certificate chain validated; mutual TLS (mTLS) for service-to-service.50- HSTS header; OCSP stapling.5152**Completion criterion:** TLS configuration documented.5354### 5. Anti-pattern audit55Check for: hardcoded keys, password-based encryption (use KDF: Argon2id / scrypt), ECB mode, no MAC on encrypted data, IV reuse, missing key rotation, weak random, deprecated algorithms (MD5, SHA1 for signatures), lack of forward secrecy.5657**Completion criterion:** anti-patterns listed; each fixed or documented with justification.5859### 6. Deliver60Cryptographic design document + implementation checklist (key lengths, modes, rotation schedule) + anti-pattern corrections.
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