December 06, 2025 · MarketReviews Team
What Is Encryption? Simple Explanation for Developers (2025 Edition)
Every time you enter your credit card information online, send a private message, or log into a website, encryption protects your data from prying eyes. As a developer in 2025, understanding encryption isn’t optional—it’s fundamental to building secure applications that users can trust. Yet many developers find cryptography intimidating, filled with complex mathematics and confusing terminology.
This comprehensive guide demystifies encryption, explaining exactly how it works, when to use different types of encryption, how it differs from hashing, and most importantly, how to implement it correctly in your applications. Whether you’re building your first web app or securing enterprise systems, this article provides the foundation you need to handle sensitive data responsibly.
What Is Encryption?
Encryption is the process of converting readable data (plaintext) into an unreadable format (ciphertext) using mathematical algorithms and keys. Only someone with the correct decryption key can transform the ciphertext back into its original plaintext form.
Think of encryption like putting a message in a locked box. Anyone can see the box, but only someone with the right key can open it and read the message inside. Without the key, the contents remain secure even if an attacker intercepts the box.
Why Encryption Matters
In today’s digital landscape, data constantly travels across networks and gets stored in databases. Without encryption, this data is vulnerable at multiple points including transmission over the internet where attackers can intercept network traffic, storage in databases or file systems that could be compromised, backups that might fall into wrong hands, and even in device memory where malware could access it.
Encryption protects data at rest (stored data), data in transit (data being transmitted), and increasingly, data in use (data being processed). It’s the primary defense against data breaches, identity theft, corporate espionage, and privacy violations.
Beyond security, encryption is often legally required. Regulations like GDPR in Europe, HIPAA for healthcare in the US, PCI DSS for payment card data, and CCPA in California mandate encryption for certain types of sensitive information. Failing to encrypt data properly can result in massive fines and legal liability.
How Encryption Actually Works
At its core, encryption relies on mathematical algorithms that transform data in ways that are easy to do with a key but virtually impossible to reverse without it.
The Basic Components
Every encryption system has four essential elements:
Plaintext: The original, readable data you want to protect. This could be a message, file, password, or any information.
Encryption Algorithm: The mathematical formula that transforms plaintext into ciphertext. Modern algorithms like AES or RSA are standardized and publicly known—security comes from the keys, not from keeping the algorithm secret.
Encryption Key: A piece of data (usually a long string of bits) that the algorithm uses to encrypt the plaintext. The same or a related key is needed for decryption.
Ciphertext: The encrypted, unreadable output. To anyone without the decryption key, ciphertext appears as random gibberish.
A Simple Example
Let’s look at a basic encryption concept using a Caesar cipher (not secure, but illustrative). If you want to encrypt the message “HELLO” with a shift of 3, you move each letter three positions forward in the alphabet: H becomes K, E becomes H, L becomes O, and so on. The encrypted message becomes “KHOOR.”
To decrypt, you simply reverse the process, shifting three positions backward. The number 3 is your key. Anyone who knows to shift by 3 can decrypt the message.
Modern encryption works on similar principles but uses far more complex mathematical operations that would take billions of years to break without the correct key.
Why Modern Encryption Is Secure
Modern encryption algorithms are designed so that even with massive computational power, breaking the encryption through brute force (trying every possible key) is practically impossible.
For example, AES-256 encryption uses 256-bit keys, meaning there are 2^256 possible keys—that’s roughly 115 quattuordecillion possibilities (a 78-digit number). Even if you could test a trillion keys per second, it would take longer than the age of the universe to try them all.
Security relies on two principles: computational infeasibility (breaking the encryption requires so much computing power and time that it’s not practical) and mathematical hardness (the underlying mathematical problems are extremely difficult to solve without the key, even knowing how the algorithm works).
Types of Encryption
There are two fundamental approaches to encryption, each suited for different use cases.
Symmetric Encryption
Symmetric encryption uses the same key for both encryption and decryption. It’s like a traditional lock and key—whoever has the key can both lock and unlock.
How Symmetric Encryption Works
You generate a secret key, use it to encrypt your plaintext producing ciphertext, and use that same key to decrypt the ciphertext back to plaintext. The key must remain secret and be shared securely with anyone who needs to decrypt the data.
Popular Symmetric Algorithms
AES (Advanced Encryption Standard): The most widely used encryption algorithm in 2025. It’s fast, secure, and comes in three key sizes: 128-bit, 192-bit, and 256-bit. AES-256 is considered extremely secure and is used by governments for classified information.
ChaCha20: A modern alternative to AES, particularly popular in mobile applications because it performs well on devices without dedicated encryption hardware. Google uses ChaCha20 in Android and Chrome.
DES and 3DES (Triple DES): Older algorithms that are now considered insecure. DES uses 56-bit keys that can be broken with modern computers. 3DES is deprecated and should not be used in new applications.
When to Use Symmetric Encryption
Symmetric encryption excels when encrypting large amounts of data like database contents or file storage, when the same entity handles both encryption and decryption, for applications where performance is critical since symmetric algorithms are fast, and when you can securely share the key with authorized parties.
The main challenge with symmetric encryption is key distribution. How do you securely share the encryption key with someone over an insecure network? If an attacker intercepts the key, they can decrypt everything.
Asymmetric Encryption (Public Key Cryptography)
Asymmetric encryption uses two mathematically related keys: a public key and a private key. Data encrypted with the public key can only be decrypted with the corresponding private key, and vice versa.
How Asymmetric Encryption Works
You generate a key pair consisting of a public key that you share openly with everyone and a private key that you keep secret and never share. When someone wants to send you encrypted data, they encrypt it with your public key. Only your private key can decrypt it.
This solves the key distribution problem. Public keys can be shared openly without compromising security because having the public key doesn’t allow decrypting messages—you need the private key for that.
Popular Asymmetric Algorithms
RSA (Rivest-Shamir-Adleman): The most widely used asymmetric algorithm. RSA key sizes typically range from 2048 to 4096 bits. While secure when used correctly, RSA is much slower than symmetric encryption.
Elliptic Curve Cryptography (ECC): Provides the same security as RSA with much smaller key sizes. A 256-bit ECC key offers security comparable to a 3072-bit RSA key. This makes ECC faster and more efficient, especially for mobile devices.
Diffie-Hellman: Not technically an encryption algorithm but a key exchange protocol. It allows two parties to establish a shared secret key over an insecure channel without ever transmitting the key itself.
When to Use Asymmetric Encryption
Asymmetric encryption is ideal for secure communication over insecure networks like the internet, digital signatures to verify authenticity and integrity, key exchange to establish shared symmetric keys securely, and authentication to verify someone’s identity.
However, asymmetric encryption is much slower than symmetric encryption—sometimes hundreds of times slower. It’s typically not used for encrypting large amounts of data directly.
Hybrid Encryption: Best of Both Worlds
Most real-world systems use hybrid encryption, combining symmetric and asymmetric approaches to get the benefits of both.
How Hybrid Encryption Works
Here’s the typical flow: First, generate a random symmetric key for the session. Use this symmetric key to encrypt the actual data (fast encryption). Encrypt the symmetric key with the recipient’s public key (asymmetric encryption). Send both the encrypted data and the encrypted symmetric key to the recipient. The recipient decrypts the symmetric key using their private key, then uses the symmetric key to decrypt the actual data.
This approach provides the security advantages of asymmetric encryption for key exchange with the performance benefits of symmetric encryption for data encryption.
Real-World Example: HTTPS
When you visit a website with HTTPS, your browser and the server use hybrid encryption. They perform an asymmetric key exchange using algorithms like RSA or ECDHE to establish a shared secret, then switch to symmetric encryption using AES for the actual data transfer, which is much faster.
This is why the initial HTTPS connection takes slightly longer than subsequent requests—the asymmetric key exchange happens at the beginning, then fast symmetric encryption handles everything else.
Encryption vs Hashing: Understanding the Difference
This is one of the most common sources of confusion for developers. Encryption and hashing are both cryptographic operations, but they serve fundamentally different purposes.
What Is Hashing?
Hashing is a one-way function that converts data of any size into a fixed-size string of characters (the hash or digest). Unlike encryption, hashing is designed to be irreversible—you cannot decrypt a hash back to the original data.
A hash function takes input data and produces a unique fingerprint. The same input always produces the same hash, but even a tiny change to the input produces a completely different hash. Good hash functions make it computationally infeasible to find two different inputs that produce the same hash (collision resistance) or to reverse-engineer the original data from the hash.
Popular Hashing Algorithms
SHA-256 (Secure Hash Algorithm): Part of the SHA-2 family, produces a 256-bit hash. Widely used and considered very secure. Bitcoin and other cryptocurrencies rely heavily on SHA-256.
SHA-3: The latest member of the Secure Hash Algorithm family, using different internal mechanisms than SHA-2 but providing similar security.
bcrypt: Specifically designed for hashing passwords, with built-in salting and adjustable computational cost to remain secure as computers get faster.
Argon2: The winner of the Password Hashing Competition, considered the gold standard for password hashing in 2025. It’s resistant to both brute force attacks and specialized hardware attacks.
MD5 and SHA-1: Older algorithms that are now considered cryptographically broken. They should never be used for security purposes, though they’re still acceptable for non-security uses like checksums.
Key Differences Between Encryption and Hashing
Reversibility: Encryption is reversible with the correct key, while hashing is designed to be one-way and irreversible.
Purpose: Encryption protects confidentiality by hiding data. Hashing verifies integrity by detecting if data has changed.
Output: Encryption output (ciphertext) is roughly the same size as the input. Hash output is always a fixed size regardless of input size.
Keys: Encryption requires keys. Hashing does not use keys (though some variants like HMAC use keys for authentication).
Use Cases: Use encryption when you need to retrieve the original data later. Use hashing when you only need to verify data hasn’t changed or to store passwords securely.
When to Use Each
Use Encryption For: Storing sensitive data you need to retrieve (like credit card numbers), transmitting confidential information over networks, protecting files and databases, and securing communications.
Use Hashing For: Storing passwords (you only need to verify if an entered password is correct, not retrieve the original), verifying file integrity (ensuring a downloaded file wasn’t corrupted or tampered with), creating unique identifiers for data, and digital signatures.
The Password Storage Example
Never encrypt passwords—always hash them. Here’s why: If you encrypt passwords and an attacker gains access to your database and encryption key, they can decrypt all passwords. If you hash passwords properly with a strong algorithm like Argon2 or bcrypt, even if an attacker gets the database, they cannot reverse the hashes to get the original passwords.
When a user logs in, you hash the password they enter and compare it to the stored hash. If they match, the password is correct. You never need to know the actual password.
Encryption Modes and Techniques
Beyond choosing an algorithm, you need to understand encryption modes and additional techniques that affect security.
Block Cipher Modes
Symmetric algorithms like AES are block ciphers—they encrypt data in fixed-size chunks (blocks). But what if your data doesn’t fit evenly into blocks, or you’re encrypting multiple blocks? That’s where modes of operation come in.
ECB (Electronic Codebook): The simplest mode that encrypts each block independently. Never use ECB—it’s insecure because identical plaintext blocks produce identical ciphertext blocks, revealing patterns in the data.
CBC (Cipher Block Chaining): Each block is XORed with the previous ciphertext block before encryption. This means identical plaintext blocks produce different ciphertext. CBC requires an initialization vector (IV) to encrypt the first block.
GCM (Galois/Counter Mode): A modern mode that provides both encryption and authentication, ensuring data hasn’t been tampered with. GCM is the preferred mode for most applications in 2025.
CTR (Counter Mode): Turns a block cipher into a stream cipher, encrypting a counter value that gets incremented for each block. CTR is fast and allows parallel processing.
Initialization Vectors (IVs) and Nonces
Most encryption modes require an IV or nonce—a random value used to ensure that encrypting the same plaintext multiple times produces different ciphertext. IVs don’t need to be secret, but they must be unpredictable and never reused with the same key.
Using the same IV with the same key for different messages can reveal information about the plaintext or allow attacks. Always generate a random IV for each encryption operation.
Salting
Salting adds random data to input before hashing, ensuring that identical inputs produce different hashes. This is crucial for password hashing because it prevents rainbow table attacks (precomputed tables of password hashes).
Each password should have a unique, randomly generated salt. The salt is stored alongside the hash and used during verification. Even if two users have the same password, their stored hashes will be completely different.
Key Derivation Functions (KDFs)
KDFs turn passwords (which are often weak) into strong encryption keys. Functions like PBKDF2, bcrypt, and Argon2 deliberately take significant time to compute, making brute force attacks impractical.
When users enter passwords, you shouldn’t use them directly as encryption keys. Instead, pass them through a KDF to derive a proper cryptographic key.
Common Encryption Mistakes Developers Make
Understanding what not to do is as important as knowing best practices.
Rolling Your Own Crypto
Never create your own encryption algorithms or implement cryptographic primitives from scratch unless you’re a cryptography expert. Modern encryption relies on subtle mathematical properties that are easy to get wrong. Even small implementation errors can completely compromise security.
Always use well-tested, peer-reviewed cryptographic libraries. In 2025, every major programming language has robust cryptography libraries built by experts.
Using Weak or Deprecated Algorithms
Algorithms that were once secure can become vulnerable as computing power increases and new attacks are discovered. Never use MD5 or SHA-1 for security purposes, DES or 3DES for encryption, or RSA keys smaller than 2048 bits.
Stay informed about cryptographic recommendations. Organizations like NIST publish guidelines on approved algorithms and key sizes.
Improper Key Management
The strongest encryption is useless if keys are poorly managed. Common mistakes include hardcoding keys in source code (which makes them accessible to anyone with access to the code), storing keys in the same database as encrypted data, using weak or predictable keys, and never rotating keys.
Keys should be stored securely in key management systems, hardware security modules (HSMs), or secure vaults. In cloud environments, use key management services like AWS KMS, Azure Key Vault, or Google Cloud KMS.
Reusing IVs or Nonces
Using the same IV or nonce with the same key for different messages can catastrophically compromise encryption. The ciphertext may reveal information about the plaintext or allow attackers to forge messages.
Always generate a fresh, random IV for each encryption operation. The IV can be transmitted or stored alongside the ciphertext—it doesn’t need to be secret.
Ignoring Authentication
Encryption provides confidentiality but doesn’t guarantee integrity or authenticity. Without authentication, attackers might modify ciphertext even if they can’t decrypt it, potentially causing security issues when the modified data is decrypted.
Use authenticated encryption modes like AES-GCM or encrypt-then-MAC approaches that verify data hasn’t been tampered with.
Encrypting Hashes or Hashing Encrypted Data
Don’t hash data and then encrypt it, or encrypt data and then hash it, without a specific reason. These combinations usually indicate misunderstanding of what encryption and hashing accomplish.
Choose the right tool for your use case: encryption for confidentiality, hashing for integrity and password storage.
Not Handling Encryption Errors Properly
Encryption and decryption can fail for many reasons including wrong keys, corrupted data, or tampered ciphertext. Handle these errors carefully to avoid leaking information through error messages or timing differences.
Don’t reveal whether decryption failed because of the wrong key versus corrupted data. Such distinctions can help attackers.
Implementing Encryption in Your Applications
Let’s look at practical implementation across different scenarios and languages.
Encrypting Data at Rest
Data at rest refers to stored data in databases, files, or backups. Encryption protects this data if storage is compromised.
For database encryption, use database-level encryption features like Transparent Data Encryption (TDE), column-level encryption for sensitive fields, or application-level encryption for maximum control. Store encryption keys separately from the database, preferably in a key management system.
For file encryption, encrypt files before writing to disk, use operating system encryption features like BitLocker or FileVault for full-disk encryption, and ensure encrypted backups of sensitive data.
Encrypting Data in Transit
Data in transit travels across networks between clients and servers. Without encryption, it can be intercepted and read by attackers.
Use TLS/SSL for all network communications. In 2025, TLS 1.3 is the standard, offering improved security and performance. Configure servers to reject older, insecure protocols like SSL 3.0 or TLS 1.0.
Use HTTPS for all web applications, even for seemingly non-sensitive sites. Modern browsers warn users about unencrypted HTTP connections, and search engines favor HTTPS sites.
For APIs, require TLS for all endpoints and consider API-level encryption for highly sensitive data even over HTTPS.
Encrypting User Passwords
Password storage deserves special attention because compromised passwords affect user accounts across multiple services.
Never store plaintext passwords. Hash passwords using bcrypt, Argon2, or scrypt with appropriate cost parameters. Generate unique salts for each password automatically. Never decrypt passwords—only verify by hashing input and comparing hashes. Implement rate limiting to prevent brute force attacks. Consider multi-factor authentication for additional security.
End-to-End Encryption
End-to-end encryption ensures only communicating parties can read messages, not even the service provider. This is how secure messaging apps like Signal and WhatsApp work.
Implement end-to-end encryption by generating key pairs for each user on their device, encrypting messages with the recipient’s public key, and decrypting on the recipient’s device with their private key. The server only handles encrypted data and cannot decrypt messages.
Code Examples by Language
Here are simple examples of encryption in popular languages:
Python with cryptography library: Use Fernet for simple symmetric encryption or implement AES-GCM for authenticated encryption. The cryptography library handles secure random number generation, proper padding, and IV management.
JavaScript with Web Crypto API: Modern browsers provide the SubtleCrypto interface for encryption operations. Use AES-GCM for authenticated encryption. For Node.js, use the built-in crypto module.
Java with javax.crypto: Use Cipher class with AES/GCM/NoPadding transformation. Generate keys using KeyGenerator and ensure proper IV handling with SecureRandom.
C# with System.Security.Cryptography: Use AesGcm class for authenticated encryption or implement AES with proper mode configuration. Ensure cryptographically secure random number generation.
Always refer to current documentation and security guidelines for your chosen language and library. Cryptographic best practices evolve, and staying current is essential.
Encryption Best Practices for 2025
Follow these guidelines to implement encryption securely.
Use Modern, Secure Algorithms
Stick with AES-256 for symmetric encryption, RSA-2048 or higher or ECC-256 for asymmetric encryption, SHA-256 or SHA-3 for hashing, and Argon2 or bcrypt for password hashing.
Avoid deprecated algorithms like DES, 3DES, MD5, SHA-1, and RC4 entirely.
Employ Authenticated Encryption
Use encryption modes that provide both confidentiality and authenticity such as AES-GCM (the preferred choice in 2025), or implement encrypt-then-MAC if GCM isn’t available.
Authentication prevents tampering and certain types of attacks that exploit unauthenticated encryption.
Manage Keys Properly
Generate keys using cryptographically secure random number generators. Never hardcode keys in application code. Store keys separately from encrypted data. Use key management services in cloud environments. Rotate keys periodically. Implement secure key backup and recovery procedures. Use different keys for different purposes.
Keep Libraries and Dependencies Updated
Cryptographic libraries regularly receive security updates. Keep all dependencies current to patch vulnerabilities. Use dependency management tools to track and update libraries. Subscribe to security advisories for libraries you use.
Implement Defense in Depth
Encryption is one layer of security. Combine it with access controls limiting who can access data, network security with firewalls and intrusion detection, secure coding practices to prevent vulnerabilities, regular security audits and penetration testing, and incident response plans for security breaches.
Comply with Regulations
Understand legal requirements for your application including GDPR requirements for data protection in Europe, HIPAA rules for healthcare data in the US, PCI DSS standards for payment card data, and CCPA regulations for California residents.
Compliance often requires specific encryption standards, key management practices, and documentation.
Document Your Cryptography
Maintain clear documentation of what data is encrypted, which algorithms and key sizes are used, how keys are managed and rotated, where encryption happens in your architecture, and recovery procedures if keys are lost.
Documentation helps security audits and ensures knowledge isn’t lost when team members change.
The Future of Encryption
Encryption continues evolving to meet emerging challenges and opportunities.
Quantum-Resistant Cryptography
Quantum computers threaten current encryption algorithms. Powerful quantum computers could break RSA and ECC encryption relatively quickly. The cryptography community is developing post-quantum algorithms resistant to quantum attacks.
NIST is standardizing post-quantum cryptographic algorithms, with several candidates in final evaluation in 2025. Organizations handling long-term sensitive data should monitor these developments and plan migration paths.
Homomorphic Encryption
Homomorphic encryption allows computations on encrypted data without decrypting it. You could send encrypted data to a cloud service, which performs calculations on the encrypted data and returns encrypted results—all without ever seeing the actual data.
While still computationally expensive, homomorphic encryption is becoming practical for specific use cases and could revolutionize privacy-preserving computation.
Zero-Knowledge Proofs
Zero-knowledge proofs allow proving you know something without revealing what you know. For example, proving you’re over 18 without revealing your exact age or birthdate.
This technology enables privacy-preserving authentication and verification, with applications in blockchain, digital identity, and compliance.
Hardware Security Modules (HSMs)
Dedicated hardware for cryptographic operations provides enhanced security by storing keys in tamper-resistant hardware, performing encryption in isolated environments, and offering faster cryptographic operations.
Cloud providers increasingly offer HSM services, making hardware security accessible without physical hardware management.
Common Encryption Terminology
Understanding these terms helps navigate cryptographic discussions:
Plaintext: Original, unencrypted data.
Ciphertext: Encrypted, unreadable data.
Cipher: An algorithm for encryption and decryption.
Key: Secret information used by the cipher to encrypt or decrypt.
Key Space: The total number of possible keys for a given algorithm.
Cryptanalysis: The study of breaking cryptographic systems.
Entropy: Randomness or unpredictability, important for keys and IVs.
Perfect Forward Secrecy: Property where compromising long-term keys doesn’t compromise past session keys.
Certificate Authority (CA): Trusted entity that issues digital certificates verifying identities.
Public Key Infrastructure (PKI): System for managing public key certificates and encryption.
Getting Started with Encryption
Ready to implement encryption in your projects? Start with understanding your security requirements and what data needs protection, learning the cryptographic features of your programming language or framework, using established libraries rather than implementing algorithms yourself, and starting with simple use cases like password hashing before tackling complex scenarios.
Practice with personal projects before implementing encryption in production systems. Study real-world implementations and open-source projects to see how experienced developers handle cryptography. Stay informed by following security researchers, reading security advisories, and participating in developer security communities.
Conclusion
Encryption is fundamental to modern application security, protecting user data, enabling secure communications, and building trust. While cryptography involves complex mathematics, developers don’t need to understand every mathematical detail—they need to understand when and how to apply encryption correctly using proven tools and libraries.
The key principles for implementing encryption successfully include using modern, vetted algorithms and libraries rather than creating your own, understanding the difference between encryption and hashing and when to use each, managing keys securely and separately from encrypted data, implementing authenticated encryption to prevent tampering, following current best practices and staying informed about cryptographic developments, and treating encryption as one layer in a comprehensive security strategy.
As cyber threats evolve and privacy concerns grow, encryption becomes increasingly important. Regulations mandate it, users expect it, and responsible development requires it. By mastering encryption fundamentals and following best practices, you can build applications that protect user data and earn user trust.
Whether you’re securing a simple web app or architecting enterprise systems, encryption knowledge is essential. Start learning today, implement carefully, and never stop improving your security practices. The data you protect matters to real people, and getting encryption right is how you honor that responsibility.
Remember: encryption is not a one-time implementation but an ongoing commitment to security. Stay current, remain vigilant, and always prioritize user privacy and data protection in your development work.