Encryption

/ˌɑːr-ɛs-ˈeɪ/

n. “Keys, math, and a little bit of trust.”

RSA is one of the most well-known public-key cryptosystems, named after its inventors Rivest, Shamir, and Adleman. Introduced in 1977, it allows secure communication over insecure channels without requiring the sender and receiver to share a secret key in advance. Instead, RSA uses a pair of mathematically linked keys: a public key for encryption and a private key for decryption.

At its core, RSA relies on the practical difficulty of factoring large numbers into their prime components. The public key consists of a modulus (the product of two large primes) and an exponent, while the private key includes information derived from the same primes. Encrypting a message with the public key ensures that only someone with the private key can decrypt it, preserving confidentiality. This asymmetry also enables digital signatures: signing a message with a private key allows anyone with the public key to verify its authenticity.

Example usage: When you connect to a secure website, your browser and the server often use RSA during the TLS handshake to exchange a symmetric session key. Even though the data itself will later be encrypted using a fast symmetric cipher like AES or GCM, RSA ensures that only the intended recipient can establish the shared key, preventing eavesdroppers from intercepting it.

Over the years, the recommended key sizes for RSA have grown due to advances in computing power. A 1024-bit key, once considered secure, is now deemed vulnerable to sophisticated attacks, whereas 2048-bit and larger keys remain widely trusted. Its security is not absolute but relies on the infeasibility of factoring massive numbers with current technology.

Beyond encryption, RSA forms the backbone of many digital signature systems, code-signing tools, and secure email protocols like PGP. It is often used alongside cryptographic hashes like SHA256 or MD5 to ensure both the integrity and authenticity of messages. For instance, a document can be hashed, and the hash encrypted with the sender’s private key to create a signature. Recipients can then decrypt with the sender’s public key and compare the hash, verifying that the document hasn’t been altered.

While modern alternatives like elliptic-curve cryptography (ECC) offer smaller keys and faster computation, RSA remains a foundational cryptographic method. Its legacy is not only technical but cultural: the algorithm helped launch the era of public-key cryptography, showing that secure communication could be achieved without pre-shared secrets.

Understanding RSA also contextualizes many concepts in cryptography, from HMAC to secure key exchange, bridging the gap between theoretical mathematics and practical cybersecurity. It proves that with primes, exponents, and a touch of mathematical elegance, trust can be built even over untrusted networks.

/ˌsiː-tiː-ˈɑːr/

n. “Turning blocks into streams, one counter at a time.”

CTR, or Counter Mode, is a mode of operation for block ciphers that transforms a block cipher into a stream cipher. Instead of encrypting plaintext blocks directly, CTR generates a key stream by encrypting successive values of a counter, then XORs this key stream with the plaintext to produce ciphertext. This approach allows parallel processing of blocks, dramatically improving performance compared to modes like CBC, which require sequential encryption.

In CTR mode, the counter is typically a combination of a nonce (number used once) and a sequential block index. Each plaintext block is XORed with the encryption of the corresponding counter value, ensuring that identical plaintext blocks yield unique ciphertext as long as the nonce is never reused. This is why proper nonce management is critical: reusing a counter with the same key undermines security.

CTR is widely used in modern cryptography, often paired with modes like GCM to provide authenticated encryption. Its parallelizability makes it ideal for high-speed network encryption, disk encryption, and secure storage systems. For example, in TLS using AES-CTR, multiple blocks of HTTP requests can be encrypted simultaneously, increasing throughput while maintaining confidentiality.

Example usage: Suppose you are encrypting a 1 GB file using AES-CTR. Each block of plaintext is XORed with the AES encryption of a counter value. The process can run on multiple CPU cores at once because each counter value is independent, allowing the entire file to be processed in parallel. Upon decryption, the same counter values are used to regenerate the key stream, restoring the original plaintext.

Security considerations for CTR include ensuring unique counter values for each encryption session. Mismanagement of counters can lead to vulnerabilities such as keystream reuse, potentially exposing plaintext through simple XOR operations. Understanding CTR also helps in grasping the design of other modes like GCM and the importance of cryptographic primitives like AES.

CTR illustrates how block ciphers can be adapted into flexible, high-performance encryption schemes. By decoupling block encryption from sequential plaintext, it paves the way for modern authenticated encryption protocols, bridging the gap between theoretical cryptography and practical, efficient security.

/ˌdʒiː-siː-ˈɛm/

n. “Authenticated encryption with speed and style.”

GCM, or Galois/Counter Mode, is a modern mode of operation for block ciphers that provides both confidentiality and data integrity. Unlike traditional encryption modes such as CBC, which only encrypts data, GCM combines encryption with authentication, ensuring that any tampering with the ciphertext can be detected during decryption.

At its core, GCM uses a counter mode (CTR) for encryption, which turns a block cipher into a stream cipher. Each block of plaintext is XORed with a unique counter-based key stream, allowing parallel processing for high performance. The “Galois” part comes from a mathematical multiplication over a finite field used to compute an authentication tag, sometimes called a Message Authentication Code (MAC), which validates that the data hasn’t been altered.

This combination makes GCM especially popular in network security protocols such as TLS 1.2 and above, IPsec, and modern disk encryption systems. Its ability to provide authenticated encryption prevents attacks that plagued older modes like CBC, including the infamous BEAST attack.

Example usage: When a client connects to a secure website using TLS with AES-GCM, the plaintext HTTP requests are encrypted using AES in counter mode, while the server verifies the accompanying authentication tag. If even a single bit of the ciphertext or associated data is modified in transit, the authentication check fails, protecting against tampering or forgery.

Benefits of GCM include parallelizable encryption for performance, integrated authentication to ensure integrity, and avoidance of padding-related issues common in CBC mode. It demonstrates the evolution of cryptographic practice: fast, secure, and resistant to attacks without relying solely on secrecy.

While GCM is robust, proper implementation is critical. Reusing the same initialization vector (IV) with the same key can catastrophically compromise security. This requirement links to the broader cryptographic principles found in SHA256, HMAC, and other authenticated primitives, showing how encryption and authentication interplay to build secure systems.

/ˌsiː-biː-ˈsiː/

n. “Chaining blocks like a linked chain of trust.”

CBC, or Cipher Block Chaining, is a mode of operation for block ciphers used in cryptography. It was designed to improve the security of block cipher encryption by ensuring that each block of plaintext is combined with the previous ciphertext block before being encrypted. This creates a “chain” effect where the encryption of each block depends on all previous blocks, making patterns in the plaintext less discernible in the ciphertext.

In practice, CBC requires an initialization vector (IV) for the first block, which is combined with the first plaintext block to prevent identical plaintexts from producing identical ciphertexts across different messages. Each subsequent block is XORed with the previous ciphertext block before encryption. This design increases security but also introduces sensitivity to certain attacks if not implemented properly.

CBC has been widely used in protocols like SSL and TLS as part of encrypting network traffic, disk encryption, and secure file storage. However, it has also been the target of attacks like BEAST and padding oracle attacks, which exploit predictable patterns or improper padding handling. These vulnerabilities highlighted the importance of secure protocol design and eventually contributed to the adoption of more robust modes such as Galois/Counter Mode (GCM) in modern TLS deployments.

Example usage: In a file encryption system, plaintext data is divided into fixed-size blocks. CBC encryption ensures that changing a single bit in one block affects all subsequent ciphertext blocks, enhancing security. Conversely, decryption requires processing blocks in sequence, as each block relies on the previous block’s ciphertext.

Despite being superseded in many contexts by authenticated encryption modes, CBC remains a foundational concept in cryptography education. Understanding CBC illuminates the challenges of chaining dependencies, handling IVs correctly, and mitigating known vulnerabilities. It also connects to related terms such as BEAST, POODLE, and other cipher modes, showing the evolution of secure encryption practices.

/biːst/

n. “The cipher’s hungry monster that chews SSL/TLS.”

BEAST, short for Browser Exploit Against SSL/TLS, is a cryptographic attack discovered in 2011 that targeted vulnerabilities in the SSL 3.0 and TLS 1.0 protocols. Specifically, it exploited weaknesses in the way block ciphers in Cipher Block Chaining (CBC) mode handled initialization vectors, allowing attackers to decrypt secure HTTPS cookies and potentially hijack user sessions.

The attack leveraged predictable patterns in encrypted traffic and required the attacker to be positioned as a man-in-the-middle or control a malicious script running in the victim's browser. By repeatedly observing the responses and manipulating ciphertext blocks, BEAST could gradually reveal sensitive information, such as session tokens or login credentials.

Like POODLE, BEAST exposed the risks of outdated encryption practices. At the time, many websites and applications still supported TLS 1.0 for compatibility with older browsers, inadvertently leaving users vulnerable. The attack prompted the cryptography and web community to prioritize newer TLS versions (1.1 and 1.2) and more secure cipher suites that properly randomize initialization vectors.

Mitigating BEAST involved disabling weak cipher suites, upgrading to TLS 1.1 or TLS 1.2, and applying browser and server patches. Modern web infrastructure now avoids the vulnerable configurations entirely, rendering BEAST largely a historical lesson, though its discovery reshaped best practices for secure web communication.

Example in practice: Before mitigation, an attacker on the same Wi-Fi network could intercept encrypted requests from a victim’s browser to an online banking site, exploiting the CBC weakness to recover authentication cookies. Once detected, web administrators were compelled to reconfigure servers and push browser updates to close the vulnerability.

BEAST is remembered as a turning point in web security awareness. It emphasized that encryption is not just about having HTTPS or TLS enabled — the implementation details, cipher choices, and protocol versions matter deeply. Its legacy also links to other cryptographic terms like SSL, TLS, and vulnerabilities such as POODLE, showing how a chain of interrelated weaknesses can endanger users if left unchecked.

/ˈpuːdəl/

n. “The sneaky browser bite that ate SSL.”

POODLE, short for Padding Oracle On Downgraded Legacy Encryption, is a security vulnerability discovered in 2014 that exploited weaknesses in older versions of the SSL protocol, specifically SSL 3.0. It allowed attackers to decrypt sensitive information from encrypted connections by taking advantage of how SSL handled padding in block ciphers. Essentially, POODLE turned what was supposed to be secure, encrypted communication into something leak-prone.

The attack worked by tricking a client and server into using SSL 3.0 instead of the more secure TLS. Because SSL 3.0 did not strictly validate padding, an attacker could repeatedly manipulate and observe ciphertext responses to gradually reveal plaintext data. This meant cookies, authentication tokens, or other sensitive information could be exposed to eavesdroppers.

The discovery of POODLE highlighted the danger of backward compatibility. While servers maintained support for older protocols to ensure connections with legacy browsers, this convenience came at the cost of security. It became a clarion call for deprecating SSL 3.0 entirely and enforcing the use of modern TLS versions.

Mitigation of POODLE involves disabling SSL 3.0 on servers and clients, configuring systems to prefer TLS 1.2 or higher, and applying proper cipher suite selections that do not use insecure block ciphers vulnerable to padding attacks. Modern browsers, operating systems, and web servers have implemented these safeguards, making the POODLE attack largely historical but still a cautionary tale in cybersecurity circles.

Real-world impact: Any organization still running SSL 3.0 when POODLE was revealed risked exposure of session cookies and user authentication data. For instance, a public Wi-Fi attacker could intercept a victim’s shopping session or corporate credentials if the server allowed SSL 3.0 fallback. Awareness of POODLE encouraged administrators to audit all legacy encryption support and prioritize secure protocols.

POODLE is now remembered less for widespread damage and more as an iconic example of how legacy support, even well-intentioned, can introduce critical vulnerabilities. It underscores the ongoing tension between compatibility and security, reminding us that in cryptography and networking, old protocols rarely stay harmless forever.

/ˌɛs-ɛs-ˈɛl/

n. “The grandparent of TLS, keeping secrets before it got serious.”

SSL, or Secure Sockets Layer, is the predecessor to TLS and was the original cryptographic protocol designed to secure communications over the internet. Developed by Netscape in the mid-1990s, SSL enabled encrypted connections between clients and servers, protecting sensitive information like passwords, credit card numbers, and private messages from eavesdropping or tampering.

Much like TLS, SSL relied on a combination of asymmetric encryption for key exchange, symmetric encryption for the actual data transfer, and hashing algorithms such as MD5 or SHA1 for data integrity. Certificates issued by trusted Certificate Authorities (CAs) authenticated server identities, helping users ensure they were connecting to legitimate services rather than impostors.

Over time, vulnerabilities in SSL were discovered, including attacks like POODLE and BEAST, which exploited weaknesses in older versions (SSL 2.0 and SSL 3.0). These flaws prompted the development of TLS, which improved security, streamlined the handshake process, and eliminated legacy vulnerabilities. Today, SSL is considered obsolete, and modern browsers and servers have deprecated its use entirely.

Despite being largely retired, SSL remains historically significant. It laid the groundwork for secure e-commerce, encrypted email, and safe browsing. Understanding SSL helps contextualize why TLS exists, how certificate authorities operate, and why cryptographic handshakes are crucial in modern network security.

Example in practice: before TLS became the standard, an online store might have used SSL to encrypt credit card transactions between a user’s browser and the payment gateway. Though the protocol had vulnerabilities by today’s standards, it provided a first layer of protection and instilled early trust in online commerce.

In essence, SSL is the cryptographic ancestor of all secure internet communications, the blueprint from which TLS was born. It reminds us that every protocol has its era, every cipher its lifespan, and that security is a constantly evolving pursuit.

/ˌtiː-ɛl-ˈɛs/

n. “Encrypts it so nobody can peek while it travels.”

TLS, or Transport Layer Security, is the cryptographic protocol that ensures data transmitted over networks remains private, authentic, and tamper-proof. It evolved from the older SSL (Secure Sockets Layer) protocols and has become the foundation of secure communication on the internet. Websites, email servers, VPNs, and numerous other networked services rely on TLS to protect sensitive information like passwords, credit card numbers, and personal communications.

At its core, TLS uses a combination of symmetric encryption, asymmetric encryption, and hashing functions to secure data. Asymmetric encryption (often using RSA or ECC keys) establishes a secure handshake and exchange of session keys. Symmetric encryption (AES, ChaCha20) encrypts the actual data, while hashing algorithms like SHA256 ensure integrity, detecting if any information was altered during transit.

Beyond encryption, TLS authenticates the parties communicating. Certificates issued by trusted Certificate Authorities (CAs) confirm the identity of servers, ensuring that users aren’t connecting to malicious impostors. The “padlock” in your browser’s address bar signals that TLS is actively securing the session.

A real-world example: when you log into a webmail account, TLS ensures that your username, password, and emails cannot be intercepted or modified by eavesdroppers on public Wi-Fi. Similarly, APIs between applications rely on TLS to protect data integrity and prevent man-in-the-middle attacks.

TLS also integrates with other security mechanisms. Protocols like HMAC may be used alongside TLS to validate message authenticity. It’s crucial for defending against attacks such as session hijacking, packet sniffing, and replay attacks, which can compromise user privacy and system security.

Modern implementations, such as TLS 1.3, have simplified the handshake process, improved performance, and removed legacy vulnerabilities present in earlier versions. Websites, cloud services, and secure communications heavily depend on these advancements to maintain trust and reliability in digital interactions.

In essence, TLS is the silent guardian of online communication, quietly encrypting and authenticating the flow of data. Without it, the digital world would be exposed to interception, tampering, and impersonation, making secure e-commerce, confidential messaging, and trusted APIs impossible.