Encryption Pattern

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

• [ ] Using AES with minimum 128-bit keys
• [ ] Using authenticated encryption mode (GCM/CCM)
• [ ] No ECB mode
• [ ] No deprecated ciphers (DES, 3DES for new data)
• [ ] RSA minimum 2048 bits (prefer 3072)
• [ ] No RSA-PKCS#1 v1.5
• [ ] Keys used for single purpose only
• [ ] Nonces/IVs from cryptographically-secure generator
• [ ] Plaintext flow analyzed for leaks
• [ ] Library supports recommended ciphers
• [ ] Designed for algorithm/key transitions

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/9901002__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

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: igbuend
• Source: igbuend/grimbard
• License: MIT

Install and usage instructions live in the source repository linked above.