Cryptography terms
The mathematics keeping secrets in an adversarial world
Cryptography is the foundation of secure communication, authentication, and data integrity across the internet. This category covers symmetric and asymmetric encryption, hashing, digital signatures, TLS, key exchange protocols, and the common mistakes developers make when implementing or misapplying cryptographic primitives. Use libraries — but understand what they are doing.
More on Cryptography
History
Cryptography evolved from ancient manual ciphers like Caesar's cipher into a rigorous mathematical discipline following Claude Shannon's 1949 information theory work, which established the theoretical foundations for secure communication. The field underwent a paradigm shift in the 1970s with the introduction of public-key cryptography (Diffie–Hellman, RSA) and digital signatures, moving beyond symmetric-key systems that required secure key distribution. The 1980s and 1990s saw standardization efforts (DES, then AES) and widespread adoption in commercial systems, while SSL/TLS emerged as the internet's primary security protocol. Modern cryptographic practice has become central to software development, addressing new challenges including quantum computing threats, forward secrecy in ephemeral sessions, and cryptographic agility in APIs. Today, developers rely on vetted libraries and standards rather than implementing cryptography from scratch, reflecting the maturation of both the field and recognition that secure-by-default practices require specialist infrastructure and continuous security auditing.
Key concepts
- Cryptographic Hash Functions
- Symmetric Encryption
- Asymmetric Encryption
- Public Key Infrastructure (PKI)
- Digital Signatures
- Encryption in Transit
- Encryption at Rest
- TLS Certificate Lifecycle
Best references
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NIST Special Publication 800-175B: Guideline for Using Cryptographic Standards in the Federal Government – Cryptographic Mechanisms Authoritative U.S. government guidance on approved cryptographic algorithms and their proper application across all 17 terms in this category.
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RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 IETF standard specification covering encryption in transit, digital signatures, key derivation, and certificate lifecycle fundamentals.
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RFC 6234: US Secure Hash and HMAC Algorithms Definitive technical reference for cryptographic hash function standards (SHA-1, SHA-2, SHA-3) and HMAC implementation.
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OWASP Cryptographic Storage Cheat Sheet Practical guidance on encryption at rest, symmetric/asymmetric encryption selection, and common cryptographic implementation mistakes.
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RFC 3394: Advanced Encryption Standard (AES) Key Wrap Algorithm Standard specification for key wrapping and secure key derivation, central to encryption at rest and PKI practices.
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"Cryptography Engineering" by Schneier, Ferguson, and Kohno (2010) Seminal industry reference covering threat modeling, algorithm selection, and real-world cryptographic system design across all category topics.
✦ Latest in Cryptography
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Edges touching a Cryptography term.
- Encryption in Transit Leverages HMAC Construction 4d
- HMAC Construction Contrasts with Digital Signatures Sep 25
- Key Derivation Functions Leverages HMAC Construction Sep 24
- JWT Deep Dive Leverages HMAC Construction Sep 24
- HMAC Construction Leverages Cryptographic Hash Functions Sep 23
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Key Rotation Strategies
The scheduled replacement of cryptographic keys before expiry or compromise, limiting the blast radius of any single key being leaked or attacked.
CWE-320 OWASP A02:2021 Cryptographic Failures
1mo ago
Cryptography advanced
6.5
Cryptographic Agility
The ability to swap cryptographic algorithms, key sizes, and protocols without rewriting application code or breaking deployed data.
2mo ago
Cryptography advanced
Envelope Encryption
PHP 7.2+
A two-layer scheme where data is encrypted with a per-object data key (DEK), which is itself encrypted by a separately managed key encryption key (KEK).
CWE-311 OWASP A02:2021-Cryptographic Failures
2mo ago
Cryptography advanced
6.5
HMAC Construction
PHP 5.1+
5
HMAC combines a secret key with a cryptographic hash via a nested keyed construction — providing message authentication that resists length-extension attacks.
CWE-353 OWASP A02:2021 Cryptographic Failures
3mo ago
Cryptography intermediate
7.5
Forward Secrecy
PHP 7.4+
A key-exchange property where ephemeral session keys are discarded after use, so a future compromise of long-term keys cannot decrypt past sessions.
CWE-327 OWASP A02:2021-Cryptographic Failures
4mo ago
Cryptography advanced
5.9
OAuth 2.0 PKCE — Proof Key for Code Exchange
PHP 7.0+
2
An OAuth 2.0 extension that prevents authorisation code interception attacks in public clients (SPAs, mobile apps) by binding each authorisation request to a cryptographic secret the client generates.
7mo ago
Cryptography intermediate
TLS Certificate Lifecycle
The end-to-end process of generating, validating, issuing, deploying, monitoring, and renewing a TLS certificate — and what breaks at each stage when it goes wrong.
7mo ago
Cryptography intermediate
Block Cipher Modes
PHP 7.1+
1
How a block cipher (AES) processes data larger than one block — ECB is insecure, CBC requires a MAC, GCM provides authenticated encryption and is the correct choice.
7mo ago
Cryptography advanced
Certificate Transparency Logs
1
Public append-only logs of all issued TLS certificates — enabling detection of misissuance and rogue certificates within hours rather than months.
7mo ago
Cryptography advanced
Cryptographic Hash Functions
PHP 5.1+
5
One-way functions producing a fixed-length digest — SHA-256, SHA-3, and BLAKE3 are secure for data integrity; MD5 and SHA-1 are broken and must not be used for security.
7mo ago
Cryptography intermediate
Cryptography Common Mistakes
PHP 7.1+
1
IV reuse, ECB mode, rolling your own crypto, timing vulnerabilities, and SHA-256 for passwords — the most frequent implementation errors.
7mo ago
Cryptography intermediate
Encryption in Transit
2
Encrypting data moving between systems using TLS — protecting against interception, tampering, and man-in-the-middle attacks on all network communication.
7mo ago
Cryptography intermediate
Post-Quantum Cryptography
3
CRYSTALS-Kyber (ML-KEM) and CRYSTALS-Dilithium (ML-DSA) standardised by NIST in 2024 — designed to resist attacks from quantum computers.
7mo ago
Cryptography advanced
Secret Sharing — Shamir's Scheme
Splitting a secret into N shares where any K can reconstruct it — preventing single points of failure for root encryption keys and disaster recovery credentials.
7mo ago
Cryptography advanced
Asymmetric Encryption
PHP 5.0+
3
A cryptographic system with a public key (shared freely) and a private key (kept secret) — data encrypted with the public key can only be decrypted with the private key.
7mo ago
Cryptography advanced
Digital Signatures
PHP 5.0+
8
Cryptographic proof that data was created by the holder of a private key and has not been altered — providing authentication, integrity, and non-repudiation.
7mo ago
Cryptography advanced
Encryption at Rest
PHP 7.0+ Encrypting stored data so that physical access to storage media does not expose plaintext — protecting against data theft from stolen drives, decommissioned hardware, and storage breaches.
7mo ago
Cryptography advanced
JWT Deep Dive
PHP 7.0+
5
JSON Web Tokens carry signed (or encrypted) claims — three Base64url-encoded sections: header.payload.signature. Security depends entirely on algorithm choice and verification correctness.
7mo ago
Cryptography advanced
Key Derivation Functions
PHP 5.5+
7
KDFs (PBKDF2, bcrypt, scrypt, Argon2) derive a cryptographic key from a password by being intentionally slow — making brute-force attacks computationally infeasible.
7mo ago
Cryptography advanced
Public Key Infrastructure (PKI)
1
The system of certificate authorities, certificates, and protocols that establishes trust in public keys — enabling HTTPS, code signing, and email encryption at internet scale.
7mo ago
Cryptography advanced