Integrity

/ɛm æk/

n. “Trust the message — not the path it traveled.”

MAC, short for Message Authentication Code, is a cryptographic construct designed to answer a deceptively simple question: has this message been altered, and did it come from someone who knows the secret? A MAC provides integrity and authenticity, but not secrecy. The contents of the message may be visible — what matters is that any tampering is detectable.

At its core, a MAC is generated by combining a message with a shared secret key using a deterministic algorithm. The result is a fixed-length tag that accompanies the message. When the message is received, the same computation is performed using the same key. If the tags match, the message is accepted. If they differ, the message is rejected outright.

Unlike digital signatures, MACs rely on symmetric trust. Both sender and receiver possess the same secret key. This makes MACs fast and efficient, but it also means they do not provide non-repudiation. Any party with the key could have generated the message. MACs prove membership in a trusted circle — not individual identity.

Many modern MAC constructions are built on top of other cryptographic primitives. HMAC combines a cryptographic hash function such as SHA256 with a secret key in a structure designed to resist collision and length-extension attacks. CMAC derives authentication from block ciphers like AES. Poly1305 uses polynomial math and is optimized for speed, provided each key is used only once.

In practice, MACs are rarely used in isolation anymore. They are most often embedded inside AEAD constructions, where encryption and authentication are inseparable. Algorithms like ChaCha20-Poly1305 and AES-GCM integrate a MAC directly into the encryption process, ensuring that ciphertext cannot be modified without detection.

Correct verification is as important as correct generation. MAC comparisons must be performed in constant time to avoid leaking information through timing side channels. A mathematically sound MAC can still fail catastrophically if implemented carelessly.

A MAC does not hide data. It does not decide who should be trusted. It does not forgive errors. It performs one role with brutal clarity: ensure that a message arrives exactly as it was sent, from someone who knows the secret.

In modern cryptography, MACs are foundational — quiet, efficient, and unforgiving. When they fail, it is rarely subtle.

/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.

/ˌes-eɪtʃ-ˈtuː/

n. “Stronger. Longer. Smarter.”

SHA2 is a family of cryptographic hash functions designed to succeed SHA1. Introduced by the NSA in the early 2000s, it addresses the weaknesses and collisions that began to appear in SHA1 while offering a flexible, robust, and modern hashing solution. Instead of a single algorithm, SHA2 includes multiple variants such as SHA-224, SHA-256, SHA-384, and SHA-512, each producing a fixed-length fingerprint that represents arbitrary input data, from files and passwords to entire software releases.

The design principle is simple but powerful: no matter the size or complexity of the input, SHA2 outputs a deterministic digest that is practically impossible to reverse or duplicate accidentally. Even the smallest change to the input causes a drastically different output, demonstrating the avalanche effect. This makes SHA2 ideal for verifying data integrity, ensuring authenticity, and establishing trust in digital systems.

Historically, the evolution of SHA2 mirrors the decline of older hash functions like MD5 and SHA1. While MD5 was fast but weak, and SHA1 initially stronger but eventually vulnerable to collisions, SHA2 was engineered to withstand modern computational attacks. Its adoption quickly spread across TLS certificates, digital signatures, Git repositories, blockchain systems, and software verification processes. Today, if you download a program or check a critical system file, chances are the checksum is a SHA2 variant.

Developers choose specific SHA2 variants based on security and performance needs. For instance, SHA-256 balances speed and cryptographic strength, while SHA-512 maximizes security for high-risk applications. Compared to SHA1, the longer digest size makes collisions astronomically improbable and brute-force attacks significantly more expensive.

In practical terms, SHA2 can be used to verify downloads, ensure password integrity when combined with proper salting techniques, and confirm the authenticity of digital signatures, Git commits, or blockchain blocks. For example, a software developer might publish a SHA-256 checksum alongside an installation package. Users who download the package can recompute the hash and compare it against the published checksum to ensure the file hasn’t been altered or tampered with. This approach replaces earlier MD5-based integrity checks that are no longer considered secure.

Despite its strength, SHA2 is not a magic shield. It does not encrypt data, and its security depends on proper implementation. Side-channel attacks, poor handling, or weak system designs can still compromise the intended protections. Nevertheless, SHA2 remains a foundation of modern hashing, bridging the gap between legacy systems and today’s security demands.

In essence, SHA2 is the evolution of the hash function: a reliable, predictable, and robust tool that ensures the fingerprints we rely on are trustworthy, whether for software distribution, digital communications, or cryptographic verification.

/ˌes-eɪtʃ-ˈwʌn/

n. “Good enough… until it wasn’t.”

SHA1 is a cryptographic hash function born in an era when the internet still believed in handshakes, trust, and the idea that computational limits would politely remain limits. Designed by the NSA and standardized in the mid-1990s, SHA1 takes arbitrary input and produces a 160-bit fingerprint — a fixed-length digest meant to uniquely represent data, documents, passwords, or entire software releases.

For years, it bridged the gap between MD5’s fragile optimism and modern hashing standards. SHA1 found use in digital signatures, TLS certificates, Git object verification, and software distribution. It was faster, longer, and seemed more reliable than MD5, providing a sense of cryptographic reassurance that we now know was temporary.

Collisions were once purely theoretical — two different inputs generating the same hash — but in 2017, the first real-world collision proved SHA1 could no longer guarantee authenticity. It could still detect accidental corruption, but intentional tampering became plausible. SHA1 does not encrypt. It does not protect secrets. It remembers — imperfectly.

Despite weaknesses, SHA1 persists in legacy systems, Git repositories, and archival documentation. It offers a historical lesson: understanding why MD5 failed and why SHA256 or other members of the SHA2 family exist. Using SHA1 teaches about integrity verification, the avalanche effect, and why modern applications demand stronger hashes.

In practice, SHA1 is still encountered when checking file integrity or verifying data has not accidentally changed. For example, Git repositories originally used SHA1 to uniquely identify commits. If two commits accidentally had identical content, the SHA1 hash would differ, signaling a change. However, today, developers are migrating to stronger hashes like SHA256 to prevent deliberate tampering, ensuring authenticity and security in a modern context.

SHA1 is a reminder that cryptography evolves — what was once trustworthy can become vulnerable, and vigilance is the only guarantee. Understanding SHA1 provides insight into the world of hashing, integrity verification, and the evolution toward secure modern standards.