Cryptography Essentials

AES Encryption Explained

Advanced Encryption Standard (AES) is the foundation of modern data security. Learn what AES is, how it works, and why it remains secure.

By GetLocalTools Editorial Team Reviewed under Editorial Policy Published: August 2, 2026 34 min read

AES encryption diagram explaining rounds of mathematical matrix transformations

Cryptography Core Concepts

AES (Advanced Encryption Standard) is a symmetric block cipher selected by the NIST in 2001 to encrypt sensitive government and enterprise data. It processes data in 128-bit blocks using key lengths of 128, 192, or 256 bits, applying repetitive rounds of mathematical matrix transformations to scramble plaintext into ciphertext.

Table of Contents

1. What Is AES Encryption?
2. Symmetric vs. Asymmetric Cryptography
3. AES Key Sizes (128 vs. 192 vs. 256)
4. How AES Works (Inside the Transformation Rounds)
5. Cipher Modes of Operation
6. Common AES Implementations
7. Advantages & Limitations
8. Frequently Asked Questions (30 FAQs)

1. What Is AES Encryption?

Advanced Encryption Standard (AES) is a symmetric block cipher chosen by the US National Institute of Standards and Technology (NIST) in 2001 to replace the aging Data Encryption Standard (DES). AES was designed by Belgian cryptographers Joan Daemen and Vincent Rijmen under the name Rijndael. To see how AES secures portable document formats, read our detailed guide on how secure are password-protected PDFs.

Today, AES serves as the primary cryptographic backbone for securing web traffic (HTTPS), encrypting database servers, protecting cloud files, and locking virtual private networks (VPNs).

2. Symmetric vs. Asymmetric Cryptography

AES belongs to the symmetric key family, which differs significantly from asymmetric algorithms like RSA. Under symmetric setups, the same key is used for both locking and unlocking. This exact mechanism is used to password protect Word documents and password protect Excel files, converting user passwords into cryptographic keys.

Metric	Symmetric Cryptography (AES)	Asymmetric Cryptography (RSA)
Key Configuration	Uses a single, shared secret key to both encrypt and decrypt data.	Uses a public key to encrypt and a separate private key to decrypt.
Performance	🟢 Fast (Highly efficient for processing large files or streams)	🔴 Slow (Computationally expensive, used for small key exchanges)
Use Cases	File encryption, secure local databases, document lockers.	TLS handshake exchanges, secure email setup, digital signatures.

3. AES Key Sizes (128 vs. 192 vs. 256)

AES supports three key lengths, each requiring a different number of mathematical rounds to transform plaintext into ciphertext. For instance, corporate entities routinely password protect PowerPoint presentations containing key intellectual property using AES-256 keys to prevent unauthorized board-level access.

Key Size	Key Combinations	Transformation Rounds	Security Application
AES-128 bit	\(3.4 imes 10^{38}\)	10 rounds	Standard business data encryption.
AES-192 bit	\(6.2 imes 10^{57}\)	12 rounds	Legacy corporate configurations.
AES-256 bit	\(1.1 imes 10^{77}\)	14 rounds	Government classified data, banks, password vaults.

4. How AES Works (Inside the Transformation Rounds)

AES operates on a 4x4 matrix of bytes called the State. The encryption process consists of several rounds of mathematical operations:

⚙️ AES Encryption Round Steps

SubBytes

→

ShiftRows

→

MixColumns

→

AddRoundKey

In each round, AES applies four distinct transformations: **SubBytes** (non-linear byte substitution using an S-Box table), **ShiftRows** (transposing rows of the state), **MixColumns** (linear multiplication of columns), and **AddRoundKey** (XORing the state with a round key derived from the main password key schedule).

5. Cipher Modes of Operation

To encrypt larger files, AES must chain multiple blocks of data together using a mode of operation. For example, when you password protect a PDF, the utility applies block cipher modes to secure the file container. If you need to recover access, you can learn how to unlock a password-protected PDF safely without uploading it to third-party servers.

ECB (Electronic Codebook): Encrypts each block independently. Insecure because identical blocks yield identical ciphertext, exposing visual patterns.
CBC (Cipher Block Chaining): XORs each plaintext block with the previous ciphertext block before encryption. Requires an Initialization Vector (IV).
GCM (Galois/Counter Mode): Provides both encryption and integrity authentication, making it the modern standard for secure web traffic.

6. Common AES Implementations

AES encryption is built into many daily productivity applications and file formats:

Office Documents: Modern Word, Excel, and PowerPoint documents (.docx, .xlsx, .pptx) use AES-256 to encrypt files when locked. Learn more in our guides: Password Protect Word → and Password Protect Excel →.
PDF Documents: Modern PDF 2.0 standards support AES-256 bit encryption. Learn about PDF security parameters in our guide: How Secure Are PDFs? →.
Web Browsers: The Web Crypto API allows browsers to encrypt and decrypt files locally in device memory. Learn why local browser processing is safer in our guide: Browser vs Cloud Tools →.

7. Advantages & Limitations

AES is the global standard for symmetric encryption, but it has specific trade-offs:

Pros: Extremely fast performance, low memory footprint, and highly secure against brute-force attacks.
Cons: Requires a secure separate channel to share keys, and file security depends entirely on password strength. Learn how to clean file metadata before encrypting in our guide: What Is File Metadata? →.

8. Frequently Asked Questions

Advanced Encryption Standard (AES) is a symmetric block cipher algorithm chosen by the US government to protect classified information and encrypt data globally.

Symmetric encryption is a cryptographic system where the same key or password is used to both encrypt (lock) and decrypt (unlock) the data.

AES-128 uses a 128-bit key and requires 10 rounds of transformation, while AES-256 uses a 256-bit key and requires 14 rounds, providing much greater security.

No. There are no known practical attacks that can crack a properly implemented AES-256 encryption key. A brute-force attack would take billions of years using modern computers.

AES is called a block cipher because it encrypts data in fixed-size blocks of 128 bits (16 bytes) at a time, rather than individual bits.

Each transformation round in AES consists of four steps: SubBytes, ShiftRows, MixColumns, and AddRoundKey.

AES is used to encrypt database records, lock Word/Excel files, secure HTTPS traffic, manage passwords in vault managers, and power virtual private networks (VPNs).

AES is symmetric (uses one key) and is fast for large files. RSA is asymmetric (uses a public and private key pair) and is slower, typically used for secure key exchanges.

No. Formatting variables only updates visual spacing without changing the underlying cryptographic key data.

Yes. Private browser utilities can run local Web Crypto API algorithms in your browser memory to decrypt files. Try our free tool: PDF Password Protector →.

A brute-force attack is an automated attempt that tries every possible key combination until the correct password is found.

AES uses a key derivation function (like PBKDF2) to turn your password into the cryptographic key. A weak password yields a key that is easy to crack.

Gzip only compresses the file size. It does not affect the encryption strength, though it is best practice to compress files before encrypting them.

AES-192 is an intermediate standard that uses a 192-bit key and requires 12 transformation rounds.

Yes. The Rijndael cipher, which became AES, was selected through an open public contest hosted by the NIST in 1997.

The key schedule is a formula that expands the original single key into multiple separate round keys, one for each round of encryption.

No. Grover's algorithm reduces the effective security of AES-256 to 128 bits, which still remains secure against all known hacking attempts.

Rijndael is the symmetric key block cipher family designed by Joan Daemen and Vincent Rijmen that was chosen as the AES standard.

Yes, when used in feedback modes like Cipher Feedback (CFB) or Counter Mode (CTR), AES can operate as a stream cipher.

Encryption secures the file's main contents, but basic container parameters and filenames may still be exposed unless metadata is cleaned. Learn more: Remove PDF Metadata →.

CBC is a mode of operation where each block of plaintext is XORed with the previous ciphertext block before being encrypted, preventing identical blocks from yielding identical ciphers.

Electronic Codebook (ECB) mode encrypts identical plaintext blocks into identical ciphertext blocks, exposing patterns in the encrypted data.

It uses the Web Crypto API built into modern browsers to run local decryption and encryption within browser sandbox memory.

AES-256 provides the highest level of cryptographic security, ensuring national intelligence remains secure against well-funded attacks.

Yes. WebP format supports EXIF metadata tags. Read our guide to learn more: EXIF Metadata Explained →.

Open the file, go to File > Info > Check for Issues > Inspect Document. Run the Document Inspector to clean properties. Learn more: Remove Office Metadata →.

Password-Based Key Derivation Function 2 is a key derivation standard that applies a pseudorandom function to passwords along with salt to yield a cryptographic key.

An IV is a random block of data used to initialize the encryption algorithm, ensuring that encrypting identical plaintexts with the same key yields different ciphers.

Client-side processing runs code locally in your browser sandbox, preventing files from being sent to external clouds. Compare standards in our guide: Browser vs Cloud Tools →.

Key length measures the number of bits in the key used to encrypt data. Longer keys (e.g. 256 bits) provide exponentially more security.