| name | encryption-pattern |
| description | Security pattern for implementing encryption and decryption operations. Use when encrypting data for confidentiality, selecting encryption algorithms (AES, RSA), configuring cipher modes (GCM, CBC), choosing key lengths, or implementing symmetric/asymmetric encryption. Specialization of Cryptographic action pattern addressing confidentiality requirements. |
Encryption Security Pattern
Encrypt a message (data elements and/or action requests) to ensure its confidentiality with respect to entities that do not possess the correct decryption key.
Core Components
| Role | Type | Responsibility |
|---|
| EntityA | Entity | Wants to encrypt one or more data elements and/or action requests |
| EntityB | Entity | Wants to decrypt received ciphertext (may be same as EntityA) |
| Encrypter | Cryptographic Primitive | Library providing encryption action |
| Decrypter | Cryptographic Primitive | Library providing decryption action |
Note: Encrypter and Decrypter roles can be performed by a single library instance. Similarly, EntityA and EntityB can be the same entity.
Data Elements
- plaintext: Original data to be encrypted
- ciphertext: Encrypted data {plaintext}_k
- keyInfo: Information on cryptographic key (identifier or key material)
- config: Cipher configuration (algorithm, mode, parameters) - optional
Actions
- encrypt: Request to encrypt plaintext using identified key and configuration
- decrypt: Request to decrypt ciphertext using identified key and configuration
Pattern Flow
Encryption
EntityA → [encrypt(plaintext, keyInfo, config)] → Encrypter
Encrypter → [ciphertext] → EntityA
Decryption
EntityB → [decrypt(ciphertext, keyInfo, config)] → Decrypter
Decrypter → [plaintext] → EntityB
Symmetric vs. Asymmetric Encryption
Symmetric Ciphers
- Same secret key for encryption and decryption
- Fast performance
- Use for bulk data encryption
- Key distribution challenge
Asymmetric Ciphers
- Public key encrypts, private key decrypts
- Slower performance (significantly slower decryption)
- Use only for small amounts of data
- Better for key negotiation, digital signatures
Recommendation: Use symmetric ciphers for encrypting data. Use asymmetric ciphers only where appropriate (key exchange, small data).
Algorithm Recommendations
Symmetric Ciphers
| Algorithm | Key Length | Status |
|---|
| AES | 128 bits | Minimum recommended |
| AES | 256 bits | Recommended for long-term (30-50 years) |
| DES | 56 bits | Deprecated - never use |
| 3DES/TDEA | 168 bits | Deprecated - decrypt legacy only |
| Salsa/ChaCha | Variable | Use with caution (less studied than AES) |
Preferred: AES with minimum 128-bit key length. Use AES-256 for long-term protection.
Cipher Modes (for AES)
| Mode | Status | Notes |
|---|
| GCM | Recommended | Authenticated encryption |
| CCM | Recommended | Authenticated encryption |
| CBC | Acceptable | Requires separate MAC |
| CTR | Acceptable | Stream mode, needs MAC |
| ECB | Never use | Reveals patterns in plaintext |
Critical: Always use authenticated encryption modes (GCM, CCM) when possible. They provide both confidentiality AND integrity.
Asymmetric Ciphers
| Algorithm | Key Length | Status |
|---|
| RSA | 3072 bits | Recommended (≈ AES-128 security) |
| RSA | 2048 bits | Minimum acceptable |
| RSA-PKCS#1 v1.5 | Any | Avoid (padding oracle attacks) |
Note: RSA-3072 provides security strength comparable to AES-128.
Security Considerations
Reuse Existing Libraries
Specialization of Cryptographic action.Reuse existing libraries:
- Use well-known cryptographic libraries
- Verify library supports recommended ciphers
- Avoid libraries supporting only deprecated ciphers
- Consult library documentation
Use Keys for Single Purpose
Specialization of Cryptographic action.Use keys for single purpose:
- Never use encryption keys for other purposes (e.g., signing)
- Use different keys for different data types
- Symmetric key: one kind of plaintext only
- Asymmetric: public key for one kind of plaintext, private key for corresponding ciphertexts
Design for Change
Specialization of Cryptographic action.Design for change:
- Algorithms may become deprecated
- Key lengths may need to increase
- Design for easy cipher/library transitions
Authenticated Encryption
General consensus: Use authenticated encryption modes for symmetric ciphers.
Benefits:
- Provides integrity guarantees in addition to confidentiality
- Detects if ciphertext was modified after encryption (e.g., by attacker during transmission)
- Most libraries provide authenticated encryption modes for AES
Random Value Generation (Nonces/IVs)
If Entity must provide random values (nonces, initialization vectors):
- Always use cryptographically-secure generator
- OWASP provides overview of secure generators by language
- Never reuse nonce/IV with same key
Plaintext Leakage
Since plaintext needed encryption, it is likely sensitive:
- Analyze entire plaintext flow for potential leaks
- Check for caching before encryption
- Ensure plaintext doesn't leak through logs, errors, or side channels
Implementation Checklist
Related Patterns
- Cryptographic action (parent pattern)
- Cryptographic key management (key handling)
- Selective encrypted transmission (encryption in transit)
- Encrypted tunnel (channel-level encryption)
- Selective encrypted storage (encryption at rest)
- Transparent encrypted storage (storage-level encryption)
References
- Source: https://securitypatterns.distrinet-research.be/patterns/99_01_002__encryption/
- Bundesamt für Sicherheit in der Informationstechnik, 'Cryptographic Mechanisms: Recommendations and Key Lengths', BSI TR-02102-1, Mar. 2020
- N. P. Smart et al., 'Algorithms, Key size and parameters report', ENISA, Nov. 2014
- E. Barker, 'Recommendation for Key Management: Part 1 – General', NIST SP 800-57 Part 1, May 2020
- E. Barker, 'Guideline for Using Cryptographic Standards in the Federal Government: Cryptographic Mechanisms', NIST SP 800-175B, Mar. 2020
- E. Barker and A. Roginsky, 'Transitioning the Use of Cryptographic Algorithms and Key Lengths', NIST SP 800-131A rev 2, Mar. 2019
- W. Breyha et al., 'Applied Crypto Hardening', bettercrypto.org, Dec. 2018
- P. C. van Oorschot, Computer Security and the Internet - Tools and Jewels, 2020
- awesome-cryptography: https://github.com/sobolevn/awesome-cryptography
