Encryption

/ˈsɪfər/

noun — "a method for transforming information to conceal its meaning."

A Cipher is a systematic technique used to encode information, transforming readable plaintext into an obscured or encrypted form known as ciphertext, with the intent of preventing unauthorized access or understanding. Ciphers form the backbone of cryptography, enabling secure communication, data protection, and authentication across digital and analog systems. The term emphasizes the algorithmic or procedural method applied to the information rather than the message itself.

Technically, a cipher consists of two main elements: the algorithm (or set of rules defining the transformation) and, often, a key (a secret parameter that personalizes or strengthens the encryption). The combination of algorithm and key determines how plaintext is converted to ciphertext and how, or if, it can be reversed back into plaintext. Ciphers may operate on individual letters, blocks of data, bits, or entire streams, depending on the system.

There are several broad categories of ciphers:

• Substitution Ciphers — each element of plaintext is replaced with another element, such as in the classic Caesar Cipher.
• Transposition Ciphers — the positions of elements are rearranged according to a pattern or key.
• Stream Ciphers — plaintext is combined with a pseudorandom keystream, often bit by bit or byte by byte.
• Block Ciphers — plaintext is divided into fixed-size blocks, and each block is transformed independently using the algorithm and key.

# conceptual example: simple Caesar cipher
plaintext = "HELLO"
key = 3
ciphertext = ""
for letter in plaintext:
    shifted = (ord(letter) - ord('A') + key) % 26 + ord('A')
    ciphertext += chr(shifted)
# ciphertext = "KHOOR"

In modern applications, ciphers are implemented using complex mathematical operations, often involving modular arithmetic, finite fields, and bitwise operations. They form the foundation for encryption standards like AES, DES, and RSA. A robust cipher ensures that without knowledge of the key, the ciphertext cannot be feasibly reverted to its original form, even if the algorithm is known.

Conceptually, a cipher acts like a lock on a message. Anyone without the correct key or understanding of the method cannot interpret the hidden information. This distinction between the visible form (ciphertext) and the intended meaning (plaintext) underpins security in digital communications, secure storage, authentication protocols, and privacy-preserving computations.

Cipher also extends beyond classical encryption; in coding theory, it can describe systematic transformations that obscure, compress, or structure information for specific purposes. In digital systems, ciphers are implemented in software, hardware, or hybrid platforms, ensuring data confidentiality in networks, storage devices, messaging applications, and embedded systems.

Conceptually, studying ciphers involves understanding patterns, reversibility, key management, and algorithmic design. Cryptanalysts seek weaknesses or predictable patterns in ciphers, while engineers design ciphers to resist attacks and ensure confidentiality. Together, these pursuits form the discipline of cryptography, where ciphers are the practical tools for information security.

See Code, Encryption, Levenshtein Distance, Caesar Cipher, Ottendorf Cipher, Affine Cipher.

/ˌɛf iː ˈkeɪ/

noun — "file encryption key."

FEK, short for File Encryption Key, is a symmetric cryptographic key used to encrypt and decrypt the contents of a single file within systems like EFS. Each file protected by a filesystem-level encryption mechanism typically has its own unique FEK to ensure isolation and minimize the risk of large-scale data compromise if one key is exposed.

Technically, FEK is a randomly generated symmetric key, often using AES (Advanced Encryption Standard) or similar algorithms. When a file is saved, the operating system encrypts its contents using the FEK. The FEK itself is then encrypted using the public key of authorized users, creating an encrypted wrapper that allows secure sharing of the file without exposing the symmetric key directly. This hybrid approach combines the speed of symmetric encryption with the secure key distribution of asymmetric cryptography.

Operationally, writing to a file involves generating or retrieving its FEK, encrypting the data blocks with it, and storing the encrypted key in the file’s metadata. Reading the file requires decrypting the FEK using the user’s private key and then using it to decrypt the file’s contents. This process ensures that even if the raw file data is copied from disk, it remains inaccessible without the correct private key to unlock the FEK.

Example of an FEK usage workflow:

Generate random FEK for file
Encrypt file data using FEK
Encrypt FEK with user public key
Store encrypted file + encrypted FEK metadata
On read: Decrypt FEK using private key
Use FEK to decrypt file data

In practice, FEKs provide granular file-level encryption, allowing selective protection of sensitive files within the same volume or filesystem. Systems like EFS often manage thousands of FEKs transparently, enabling secure backups, authorized access delegation, and recovery without user intervention.

Conceptually, a FEK is like a personal combination lock for each file: the file’s contents are the protected item, and the FEK is the key. Only users with the corresponding unlock mechanism (private key) can retrieve the contents safely, while the operating system handles the mechanics behind the scenes.

See EFS, Encryption, Access Control.

/ˌiː ɛf ˈɛs/

noun — "encrypted file storage system."

EFS, short for Encrypting File System, is a filesystem-level encryption technology that allows individual files or directories to be transparently encrypted on storage volumes. It integrates directly with the operating system’s file management layer, providing confidentiality for sensitive data while maintaining standard access semantics for authorized users.

Technically, EFS operates by encrypting file contents using symmetric encryption keys and associating each file with an encrypted File Encryption Key (FEK). The FEK itself is secured using the user’s public key, ensuring that only authorized accounts with the corresponding private key can decrypt and access the file. Metadata, such as filenames and timestamps, may remain unencrypted to support standard file operations. Encryption and decryption are performed automatically by the operating system kernel, so applications access files normally without requiring explicit cryptographic operations.

File storage under EFS includes a reserved portion for encryption metadata, including key information, recovery certificates, and algorithm identifiers. Multiple users can be authorized for a single encrypted file by encrypting the FEK with each user’s public key. Recovery agents can decrypt files without the original user’s private key, providing administrative control over encrypted data.

Operationally, when a user writes to an EFS-protected file, the system generates a random FEK, encrypts the file contents, and stores the FEK encrypted under the user’s public key. Reading the file requires the operating system to retrieve the encrypted FEK, decrypt it using the user’s private key, and then decrypt the file data. This process is transparent to applications and ensures that unauthorized users cannot access the contents even if they have raw disk access.

Example workflow in code for encrypting a file (conceptual):

Initialize EFS context
Generate symmetric FEK
Encrypt file data using FEK
Encrypt FEK using user public key
Store encrypted file + encrypted FEK on disk

EFS is particularly useful in enterprise environments, removable storage, and laptops, where physical theft or unauthorized access could compromise sensitive information. It complements other security mechanisms such as access control lists, disk-level encryption, and backup policies.

Conceptually, EFS acts like a secure envelope for individual files: each envelope contains both the protected content and a lock that only authorized users can open, while the operating system manages the envelope seamlessly in everyday use.

See FileSystem, Encryption, FEK, Access Control.

/siː-mæk/

noun — "the cryptographic signature that proves a message hasn’t been tampered with."

CMAC, short for Cipher-based Message Authentication Code, is a cryptographic algorithm used to verify the integrity and authenticity of messages. It generates a fixed-size tag from a variable-length message using a block cipher, such as AES, ensuring that any alteration in the message can be detected.

Technically, CMAC processes the message in blocks, applies the block cipher, and produces a tag that is sent alongside the message. The recipient uses the same key and algorithm to recompute the tag and compare it with the received one. CMAC prevents forgery and ensures that messages come from authenticated sources.

Key characteristics of CMAC include:

• Message integrity: detects any changes in the message.
• Authentication: verifies that the message originates from a trusted sender.
• Keyed operation: uses a secret symmetric key for security.
• Block cipher-based: typically built on AES or similar ciphers.
• Fixed-length output: produces a consistent tag regardless of message size.

In practical workflows, CMAC is used in secure communications, payment systems, and embedded devices where integrity and authentication are critical. It is often combined with encryption protocols to provide both confidentiality and integrity.

Conceptually, CMAC is like a tamper-evident seal on a package: if the seal is broken or altered, you immediately know the contents were tampered with.

See AES, Cryptography, Digital Signature, PKI, Hash Function.

/hæʃ ˈfʌŋk.ʃən/

noun — "a function that converts data into a fixed-size digital fingerprint."

Hash Function is a mathematical algorithm that transforms input data of arbitrary length into a fixed-size value, called a hash or digest. This process is deterministic, meaning the same input always produces the same hash, but even a tiny change in input drastically changes the output. Hash Functions are widely used in data integrity verification, cryptography, digital signatures, password storage, and blockchain technologies.

Technically, a hash function takes a binary input and performs a series of transformations such as modular arithmetic, bitwise operations, and mixing functions to produce a hash value. Common cryptographic hash functions include MD5 (MD5), SHA-1 (SHA1), SHA-256 (SHA256), and SHA-512 (SHA512). These functions are designed to be fast, irreversible, and resistant to collisions, where two different inputs produce the same hash.

Key characteristics of hash functions include:

• Deterministic: the same input always generates the same hash.
• Fixed-size output: produces a consistent-length digest regardless of input size.
• Collision resistance: difficult to find two different inputs yielding the same hash.
• Pre-image resistance: infeasible to reconstruct input from its hash.
• Efficiency: capable of processing large datasets quickly.

In practical workflows, engineers use hash functions to verify file integrity, generate checksums, authenticate messages, and store passwords securely. For example, when downloading a file, a system can compute its hash and compare it to a known hash to ensure the file has not been tampered with. In blockchains, hash functions link blocks in an immutable chain, providing security and transparency.

Conceptually, a hash function is like a blender: it takes ingredients (data), mixes them thoroughly, and outputs a unique smoothie (hash) that represents the input but cannot be easily reversed.

Intuition anchor: hash functions create digital fingerprints for data, enabling verification, security, and efficient data handling.

Related links include MD5, SHA1, and SHA256.

/ˈkrɪp.təˌɡræ.fi/

noun — "the art and science of keeping information secret and verifiable."

Cryptography is the study and practice of techniques for securing communication and data from unauthorized access, manipulation, or interception. It involves transforming readable data (plaintext) into an encoded form (ciphertext) using mathematical algorithms and keys, ensuring confidentiality, integrity, authentication, and non-repudiation. Cryptography underpins secure digital communication, online banking, blockchain systems, and password protection.

Technically, cryptography encompasses symmetric-key methods, where the same key is used for encryption and decryption, and asymmetric-key methods (public-key cryptography), where a public key encrypts data and a private key decrypts it. Hash functions create fixed-length digests to verify data integrity without revealing the original content. Modern cryptography also includes digital signatures, zero-knowledge proofs, and authenticated encryption schemes for secure protocols like TLS/SSL and VPNs.

Key characteristics of cryptography include:

• Confidentiality: prevents unauthorized parties from reading sensitive data.
• Integrity: ensures data has not been altered during transmission.
• Authentication: verifies the identity of communicating parties.
• Non-repudiation: prevents senders from denying actions, often via digital signatures.
• Algorithm-driven: relies on mathematical functions, keys, and protocols to secure data.

In practical workflows, cryptography is implemented in secure messaging, online payments, data storage, and network protocols. For example, a secure website uses asymmetric cryptography to exchange a session key, which then enables symmetric encryption for faster communication. Engineers also apply hashing algorithms like SHA-256 to verify file integrity and use digital certificates to validate identity in public-key infrastructures (PKI).

Conceptually, cryptography is like sealing a message in a locked, uniquely keyed box: only someone with the correct key can open it, and any tampering is immediately detectable.

Intuition anchor: cryptography transforms information into a form that is intelligible only to those authorized, forming the invisible shield of digital trust.

/ˈiː-ɛe-dɛd/

n. “Encrypt it — and prove nobody touched it.”

AEAD, short for Authenticated Encryption with Associated Data, is a class of cryptographic constructions designed to solve two problems at the same time: confidentiality and integrity. It ensures that data is kept secret and that any unauthorized modification of that data is reliably detected.

Older cryptographic designs often treated these goals separately. Data would be encrypted using a cipher, then authenticated using a separate MAC algorithm. Done carefully, this could work — but it was fragile. Get the order wrong, reuse a nonce, authenticate the wrong fields, or forget to authenticate metadata, and the entire security model could collapse. AEAD exists to remove that footgun.

In an AEAD scheme, encryption and authentication are mathematically bound together. When data is encrypted, an authentication tag is produced alongside the ciphertext. The recipient must verify this tag before trusting or even attempting to decrypt the data. If verification fails, the data is discarded. No partial success. No ambiguity.

The “associated data” portion is subtle but powerful. It refers to information that should be authenticated but not encrypted. Examples include protocol headers, sequence numbers, or routing metadata. With AEAD, this data is protected against tampering without being hidden — a critical feature for modern network protocols.

Common AEAD constructions include ChaCha20-Poly1305 and AES-GCM. In ChaCha20-Poly1305, ChaCha20 handles encryption while Poly1305 generates the authentication tag. In AES-GCM, AES encrypts the data while Galois field math provides authentication. Different machinery — same promise.

AEAD has become the default expectation in modern cryptographic protocols. TLS 1.3 relies exclusively on AEAD cipher suites. WireGuard uses AEAD exclusively. This is not fashion — it is the accumulated lesson of decades of cryptographic mistakes.

Consider a secure message sent across a hostile network. Without AEAD, an attacker might not decrypt the message, but could flip bits, replay packets, or alter headers in ways that cause subtle and dangerous failures. With AEAD, even a single altered bit invalidates the entire message.

AEAD does not guarantee anonymity. It does not manage keys. It does not decide who should be trusted. It does one job, and it does it thoroughly: bind secrecy and authenticity together so they cannot be accidentally separated.

In modern cryptography, AEAD is not an enhancement — it is the baseline. Anything less is an invitation to rediscover old mistakes the hard way.

/ˌpɒliˈwʌn-θɜːrtiː-fʌɪv/

n. “A tiny guardian watching every bit.”

Poly1305 is a cryptographic message authentication code (MAC) algorithm created by Daniel J. Bernstein, designed to verify the integrity and authenticity of a message. Unlike encryption algorithms that hide the content, Poly1305 ensures that data has not been tampered with, acting as a digital seal that can detect even a single-bit change in a message.

Its design is simple but effective. Poly1305 treats messages as sequences of numbers and applies modular arithmetic over a large prime (2^130−5, hence the name). The resulting tag, typically 16 bytes long, is unique to the message and the secret key. Any alteration of the message results in a tag mismatch, instantly flagging tampering.

In practice, Poly1305 is rarely used in isolation. It is most commonly paired with the ChaCha20 stream cipher to form the ChaCha20-Poly1305 AEAD (Authenticated Encryption with Associated Data) construction. Here, ChaCha20 encrypts the content, while Poly1305 generates a tag to verify its authenticity. This combination provides both confidentiality and integrity simultaneously, a critical requirement for secure communications like TLS or WireGuard tunnels.

One of the standout features of Poly1305 is speed. It is optimized for modern CPUs, using simple arithmetic operations that minimize timing variability. This makes it highly resistant to side-channel attacks, a common pitfall for MAC algorithms on less carefully designed systems. Its efficiency has made it a staple in mobile and embedded applications where performance matters.

For developers, using Poly1305 correctly requires a unique key for each message. Reusing the same key for multiple messages can compromise security. Fortunately, in the typical ChaCha20-Poly1305 construction, ChaCha20 generates per-message keys, eliminating this risk.

Imagine sending a sensitive configuration file across an insecure network. Without a MAC, you wouldn’t know if it had been modified. With Poly1305, the recipient can instantly verify that the file arrived exactly as sent. Any attempt to tamper with the data — accidental or malicious — will be immediately detectable.

Poly1305 does not encrypt. It does not hide. It observes. It ensures that the message you trust is indeed the message you receive. Paired with an encryption layer like ChaCha20 or AES, it forms a complete, robust security envelope suitable for modern networking, storage, and communication applications.

In short, Poly1305 is the unsung sentinel of cryptography: small, fast, reliable, and essential whenever authenticity matters.

/ˈtʃɑː-tʃɑː-twɛn-ti/

n. “Fast. Portable. Secure — even when the hardware isn’t helping.”

ChaCha20 is a modern stream cipher designed to encrypt data quickly and securely across a wide range of systems, especially those without specialized cryptographic hardware. Created by Daniel J. Bernstein as a refinement of the earlier ChaCha family, ChaCha20 exists to solve a practical problem that older ciphers struggled with: how to deliver strong encryption that remains fast, predictable, and resistant to side-channel attacks on ordinary CPUs.

Unlike block ciphers such as AES, which encrypt fixed-size chunks of data, ChaCha20 generates a continuous pseudorandom keystream that is XORed with plaintext. This makes it a stream cipher — conceptually simple, mechanically elegant, and well suited for environments where data arrives incrementally rather than in neat blocks.

The “20” in ChaCha20 refers to the number of rounds applied during its internal mixing process. These rounds repeatedly scramble a 512-bit internal state using only additions, XORs, and bit rotations. No lookup tables. No S-boxes. No instructions that leak timing information. This arithmetic-only design is deliberate, making ChaCha20 highly resistant to timing attacks that have historically plagued some AES implementations on older or embedded hardware.

ChaCha20 is rarely used alone. In practice, it is almost always paired with Poly1305 to form an AEAD construction known as ChaCha20-Poly1305. This pairing provides both confidentiality and integrity in a single, tightly coupled design. Encryption hides the data; authentication proves it hasn’t been altered. One without the other is half a lock.

This combination is now widely standardized and deployed. Modern TLS implementations support ChaCha20-Poly1305 as a first-class cipher suite, particularly for mobile devices where hardware acceleration for AES may be absent or unreliable. When your phone loads a secure website smoothly on a weak CPU, ChaCha20 is often doing the heavy lifting.

ChaCha20 also plays a central role in WireGuard, where it forms the backbone of the protocol’s encryption layer. Its speed, simplicity, and ease of correct implementation align perfectly with WireGuard’s philosophy: fewer knobs, fewer mistakes, fewer surprises.

From a developer’s perspective, ChaCha20 is refreshingly hard to misuse. It avoids the fragile modes and padding schemes associated with block ciphers, and its reference implementations are compact enough to audit without losing one’s sanity. That simplicity translates directly into fewer bugs and fewer catastrophic mistakes.

ChaCha20 does not replace AES outright. On systems with dedicated AES instructions, AES can still be faster. But where hardware support is absent, inconsistent, or suspect, ChaCha20 often wins — not by being clever, but by being dependable.

It does not claim to be unbreakable forever. No serious cryptography does. Instead, ChaCha20 earns trust through conservative design, open analysis, and years of public scrutiny. It performs exactly the job it claims to perform, and little else.

ChaCha20 is encryption without theatrics. Arithmetic over spectacle. Reliability over bravado. A cipher built for the real world, where hardware varies, attackers are patient, and correctness matters more than tradition.

/ˌiː-siː-ˈsiː/

n. “Small curves, big security.”

ECC, or Elliptic Curve Cryptography, is a public-key cryptography system that uses the mathematics of elliptic curves over finite fields to create secure keys. Unlike traditional algorithms like RSA, which rely on the difficulty of factoring large integers, ECC relies on the hardness of the elliptic curve discrete logarithm problem. This allows ECC to achieve comparable security with much smaller key sizes, improving performance and reducing computational load.

In practice, ECC is used for encryption, digital signatures, and key exchange protocols. For example, the widely adopted ECDSA (Elliptic Curve Digital Signature Algorithm) allows you to sign messages or software releases securely while keeping key sizes small. A 256-bit ECC key provides roughly the same security as a 3072-bit RSA key, making it highly efficient for mobile devices, IoT, and other constrained environments.

Example usage: When establishing a secure connection via TLS, a server might use an ECC key pair to perform an ECDH (Elliptic Curve Diffie-Hellman) key exchange. This process allows the client and server to derive a shared secret without ever transmitting it over the network. The smaller key sizes reduce latency and CPU usage, especially important for high-traffic servers or devices with limited power.

ECC also integrates seamlessly with other cryptographic primitives. For instance, you can combine ECC with a cryptographic hash like SHA256 to produce efficient and secure digital signatures. This combination ensures both the integrity and authenticity of messages or code, similar to how RSA signatures work but with significantly less computational overhead.

Security considerations for ECC include proper curve selection and secure implementation. Certain curves, like those standardized by NIST, are widely trusted, while others may have unknown vulnerabilities. Additionally, side-channel attacks can exploit poor implementations, so using vetted cryptographic libraries is essential.

The adoption of ECC has grown rapidly, particularly in areas where performance, bandwidth, or energy efficiency matters. Mobile messaging apps, cryptocurrency wallets, VPNs, and secure email systems all leverage ECC for its compact keys and strong security properties. Understanding ECC also helps make sense of other modern cryptographic techniques, bridging the gap between the math of elliptic curves and the practical world of secure communications.

In short, ECC represents the evolution of public-key cryptography: smaller keys, faster operations, and robust security. It is both a practical solution for modern computing environments and a fascinating demonstration of how abstract mathematics can protect data across the global internet.