Encryption is the process of converting readable information into an unreadable format so that only someone with the right key can convert it back. Think of it as locking a message inside a box: anyone can see the box, but only a person with the correct key can open it and read what is inside. The concept dates back thousands of years, from ancient substitution ciphers to the complex mathematical systems that now protect everything from your text messages to your bank account. While the basic goal has never changed, the methods have grown dramatically more sophisticated, and understanding what encryption actually does (and does not do) matters more now than at any earlier point in history.
Scrambling Data So Only the Right Person Can Read It
At its core, encryption takes plaintext, which is any information in its normal, readable form, and transforms it into ciphertext using a mathematical procedure called an algorithm. The ciphertext looks like random gibberish to anyone who intercepts it. To turn it back into plaintext, the recipient needs a decryption key that reverses the process. Without that key, the ciphertext is useless.
This transformation is not the same as simply hiding data. If you tuck a letter under a mattress, it is still readable to anyone who finds it. Encryption makes the content itself unintelligible, even if someone gets their hands on the file, the network packet, or the hard drive it sits on. That distinction matters: encryption protects information regardless of where it travels or who stumbles across it.
Symmetric Encryption
The simplest form of encryption uses a single key for both locking and unlocking. This is symmetric encryption, sometimes called secret-key encryption. Both the sender and the receiver share the same key. If you and a friend agree on a secret password and use it to scramble and unscramble your notes, you are using symmetric encryption in principle.
Modern symmetric algorithms like AES (Advanced Encryption Standard) are fast and efficient. They can churn through large amounts of data quickly, which is why they handle the bulk of encryption you encounter daily: encrypting files on your laptop, protecting stored databases, and securing the actual data flowing through an internet connection once a session has been set up. The catch is that both parties need to have the same key, and getting that key to the other person securely is a genuine problem. If someone intercepts the key during delivery, they can read everything.
Asymmetric Encryption and Public-Private Key Pairs
Asymmetric encryption solves the key-sharing problem by using two different but mathematically related keys. One is made public and can be shared freely; the other stays private and is never transmitted. When someone wants to send you an encrypted message, they use your public key to lock it. Only your private key can unlock it. Because the public key cannot decrypt what it encrypted, there is no danger in handing it out openly.
As one overview of the method explains, in asymmetric encryption “one is used to encrypt the data (usually called the public key as it can be made publicly available) and the other one (called the private key) is used to decrypt the data.”1Engineering Applications of Artificial Intelligence. Learning asymmetric encryption using adversarial neural networks This approach underpins much of online security: when your browser connects to a website over HTTPS, asymmetric encryption is used first to safely exchange a symmetric session key, and then symmetric encryption takes over for speed.
The trade-off is computational cost. Asymmetric encryption relies on difficult math problems, such as factoring very large numbers, which makes it significantly slower than symmetric encryption for large data. That is why most real-world systems use a hybrid approach: asymmetric encryption to safely swap keys, then symmetric encryption for the heavy lifting of actual data transfer.
Where You Encounter Encryption Every Day
Encryption works in two main scenarios that security professionals call “data at rest” and “data in transit.” Data at rest is information sitting on a device or server: your phone’s storage, a company’s database, files on a USB drive. Encrypting data at rest means that if the device is stolen, the thief sees only scrambled bytes without the decryption key.
Data in transit is information moving across a network, such as an email traveling between servers or a credit card number being sent to an online store. Encrypting data in transit protects it from being read by anyone who intercepts the traffic along the way. When you see the padlock icon in your browser’s address bar, the connection between your device and the website is encrypted in transit using a protocol called TLS.
End-to-end encryption goes further. In a standard encrypted connection, the service provider in the middle (your email company, for instance) can still read the data because it holds the keys. With end-to-end encryption, only the sender and receiver have the keys. The service provider carries the ciphertext but cannot decrypt it. Messaging apps like Signal and WhatsApp use this model, meaning even the company running the service cannot read your conversations.
Digital Signatures and Verifying Integrity
Encryption is not only about keeping secrets. A closely related use involves proving that data has not been tampered with and that it came from who it claims to come from. This is where digital signatures enter the picture.
A digital signature works by running a message through a hash function, a mathematical process that produces a short, fixed-length string unique to that particular input. Even a tiny change to the original message produces a completely different hash. The sender then encrypts the hash with their private key. The recipient decrypts it with the sender’s public key and independently hashes the received message. If the two hashes match, the message has not been altered and it genuinely came from the claimed sender.
Cryptographic hash functions “ensure data integrity, authenticate the origin of messages, and provide non-repudiation,” meaning the sender cannot later deny having sent a signed message.2American Journal Of Cryptography And Network Security. The Role of Cryptographic Hash Functions in Secure Digital Signatures This is the backbone of software updates, legal documents, cryptocurrency transactions, and many other systems where trust in the content’s authenticity matters as much as secrecy.
Certificates and How Trust Gets Established
Having a public key is only useful if you can trust that it actually belongs to the person or organization it claims to belong to. If an attacker can swap in their own public key and trick you into thinking it is your bank’s, they can intercept everything. Public key infrastructure, or PKI, exists to solve this problem.
PKI relies on digital certificates, which are electronic documents that bind a public key to an identity. A certificate authority (CA), a trusted third party, signs these certificates using its own private key. Your browser or operating system comes pre-loaded with a list of trusted CAs, so when a website presents its certificate, your device can verify the CA’s signature and confirm that the certificate is legitimate.
The standard format for these certificates is X.509. Each certificate contains information about the subject (who owns it), the issuer (which CA signed it), validity dates, the subject’s public key and the algorithm it uses, and the CA’s signature.3Computers & Security. PKI4IoT: Towards public key infrastructure for the Internet of Things This chain of trust stretches from a root CA down through intermediate CAs to the individual certificate on a website, and your browser verifies each link in the chain every time you visit an HTTPS site. All of this happens in milliseconds, invisibly.
Encryption on Constrained Devices
Not every device that needs encryption has the processing power of a laptop or a server. The explosion of Internet of Things gadgets, from smart thermostats and fitness trackers to industrial sensors, has created a challenge. These devices are small, run on tiny batteries, and have limited memory. Running a full AES implementation can drain a sensor’s battery or slow its response time unacceptably.
Conventional encryption algorithms are “generally computationally expensive due to their complexity and requires many rounds to encrypt, essentially wasting the constrained energy of the gadgets.”4arXiv. SIT: A Lightweight Encryption Algorithm for Secure Internet of Things To address this, researchers have developed lightweight encryption algorithms that reduce the number of processing rounds or use simpler mathematical operations while still maintaining adequate security. These lighter algorithms trade some margin of cryptographic strength for dramatically lower energy and memory requirements, making it feasible to encrypt data on a device the size of a postage stamp.
The practical significance is real. A medical implant reporting heart rhythm data, a connected lock on your front door, a sensor monitoring water quality in a treatment plant: all transmit sensitive data and all benefit from encryption, but none can afford the overhead of algorithms designed for desktop processors. Lightweight cryptography is an active research field, with standardization efforts underway to establish which of these leaner algorithms are secure enough for widespread use.
The Quantum Computing Threat
Much of today’s asymmetric encryption depends on certain math problems being extremely hard for computers to solve. Factoring a very large number into its prime components, for instance, would take a classical computer longer than the age of the universe for keys of sufficient size. This difficulty is what makes systems like RSA secure.
Quantum computers threaten to upend that assumption. Shor’s algorithm, a quantum algorithm published in the 1990s, can factor large integers and solve related problems efficiently on a quantum machine. The problems underlying several widely used cryptographic systems “are generally thought to be hard on classical computers and have been used as the basis of several proposed cryptosystems,” but a sufficiently powerful quantum computer running Shor’s algorithm could break them.5SIAM Review. Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer
No quantum computer today is powerful enough to break real-world encryption keys. Current machines have too few stable quantum bits (qubits) and too high an error rate. But the concern is not just about today: encrypted data captured now could be stored by an adversary and decrypted later once a capable quantum machine exists. This “harvest now, decrypt later” scenario has pushed governments and standards bodies to act proactively.
Post-quantum cryptography (PQC) is the field dedicated to building encryption algorithms that resist quantum attacks. These new algorithms rely on different mathematical problems, ones that quantum computers are not known to solve efficiently. “The advent of quantum computing poses a profound threat to traditional cryptographic systems,” and PQC “emerged as a critical field aimed at developing resilient cryptographic algorithms impervious to quantum attacks.”6arXiv. Post-Quantum Cryptography: Securing Digital Communication in the Quantum Era The U.S. National Institute of Standards and Technology (NIST) has already selected several PQC algorithms for standardization, and organizations handling sensitive long-term data are beginning to migrate.
Encryption Does Not Protect Against Everything
A common misconception is that encrypted data is automatically safe. Encryption is powerful, but it protects a narrow thing: confidentiality (and, with signatures, integrity and authenticity) of the data itself. It does nothing about the many other ways information gets compromised.
If someone tricks you into handing over your password through a phishing email, the strongest encryption in the world will not help. The attacker does not need to break the encryption; they just log in as you. Similarly, if malware is running on your device, it can read data after your device has already decrypted it for you. Encryption protects the pipe and the storage, not the endpoints. This is why security professionals emphasize that encryption is one layer in a defense that also includes software updates, strong authentication, and user awareness.
Poor key management undermines encryption too. If a private key is stored in a predictable location, written down and taped to a monitor, or never rotated, an attacker can simply steal the key instead of trying to crack the algorithm. The algorithm itself might be theoretically unbreakable, but that is cold comfort if the key is sitting in an unprotected text file on a shared server.
Encryption, Governments, and the Backdoor Debate
Encryption creates a tension between privacy and law enforcement that has been playing out for decades. When everyone can encrypt their communications so securely that no third party, including police with a warrant, can read them, law enforcement agencies argue they lose a critical investigative tool.
This tension is often called “going dark.” As companies and individuals increasingly use end-to-end encryption, “law enforcement and national security agencies claim they ‘go dark,’ i.e. lose in practice the power to legally intercept and gain access to information and communications. This has revived a debate that seemed closed by the late 1990s, namely whether backdoors should be embedded in encryption systems.”7Computer Law & Security Review. Looking for some light through the lens of “cryptowar” history: Policy options for law enforcement authorities against “going dark”
The original “crypto wars” of the 1990s saw U.S. government proposals to mandate key escrow systems, where a copy of every encryption key would be held by a trusted party accessible to law enforcement. The proposals were abandoned, largely because security experts argued that any built-in backdoor creates a vulnerability that malicious actors can also exploit. A backdoor does not stay exclusive to the good guys; once it exists, it becomes a target.
That debate has resurfaced. Institutions on both sides of the Atlantic “are again pushing for new restrictions on encryption” in response to concerns about terrorism and child exploitation.8Computer Law & Security Review. The right to encryption: Privacy as preventing unlawful access Proposals range from requiring platforms to scan content before encryption (so-called client-side scanning) to mandating that providers retain the ability to decrypt user data on demand. Privacy advocates and cryptographers generally oppose these measures, arguing that weakening encryption for one purpose weakens it for all purposes. The debate shows no sign of resolution, and the policy landscape varies significantly by country.
Encryption Strength Is Not Permanent
An algorithm considered unbreakable today may not hold that status forever. Advances in computing power, new mathematical insights, and flawed implementations can all erode the security of a given system over time. DES, the Data Encryption Standard adopted in the 1970s, was considered robust for decades before its 56-bit key length became short enough for brute-force attacks using inexpensive hardware. It was replaced by AES, which uses key lengths of 128, 192, or 256 bits and remains secure against known attacks.
This is why cryptographic standards are periodically reviewed and updated. The transition from older protocols like SSL 3.0 and TLS 1.0 to the current TLS 1.3 reflects this ongoing process: each update retires algorithms that are no longer considered safe and adds newer, better-vetted ones. For anyone relying on encryption, whether you manage servers or simply use consumer products, keeping software up to date is one of the most effective things you can do. Updates often include patches to cryptographic libraries, and falling behind means relying on protections that the security community has already flagged as inadequate.
The quantum computing timeline adds urgency to this pattern. Even if a full-scale quantum computer capable of breaking RSA is still years or decades away, the migration to quantum-resistant algorithms is a massive infrastructure undertaking. Certificates, protocols, hardware, firmware, and embedded devices all need to be updated. Organizations that start planning and testing now will be far better positioned than those that wait until a breakthrough forces a scramble.