Overview
AES transforms a 128-bit block through rounds of byte substitution, row shifting, column mixing, and round-key addition. Secure message encryption uses AES inside an appropriate mode of operation.
FoundationSource checked
AES
Encrypts fixed-size blocks with a symmetric key using repeated substitution and permutation rounds.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Cryptography
- Difficulty
- Advanced
- Family
- Symmetric Encryption
- Tier
- Foundation
- Status
- Verified
- Review
- Source Checked
- Sources
- 1
- Formulas
- 1
- Relationships
- 11
- Code example
- Not ready
- Visualization
- Ready
Core Concepts
block cipherround keysubstitution-permutation networkmode of operation
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(n)
Average
O(n)
Worst
O(n)
Space
O(1)
When to Use
- Use AES through a vetted cryptographic library.
- Use authenticated modes such as GCM when confidentiality and integrity are both needed.
- Use it when interoperating with systems that require standardized symmetric encryption.
When Not to Use
- Avoid raw block encryption for multi-block messages.
- Avoid reusing nonces or IVs in modes that require uniqueness.
- Avoid implementing AES rounds manually for production security.
What It Does
- Encrypts blocks with a symmetric key
- Decrypts blocks with the same key
Use Cases
- Data encryption
- Secure storage
- Encrypted communication
Inputs
- Plaintext block
- Symmetric key
Outputs
- Ciphertext block
Key Formulas (1)
AES round
state = AddRoundKey(MixColumns(ShiftRows(SubBytes(state))))
state = AddRoundKey(MixColumns(ShiftRows(SubBytes(state))))Shows the main transformation sequence used in a standard AES round.
Pseudocode
- 1.Expand the secret key into round keys
- 2.Mix the first round key into the block
- 3.Apply repeated substitution and permutation rounds
- 4.Mix in a round key each round
- 5.Return the encrypted block
Canonical Example
- Input
- plaintext block, AES key, and mode-specific nonce or IV
- Output
- ciphertext and authentication tag when using an authenticated mode
- Explanation
- AES encrypts blocks under the key, while the mode controls how blocks and nonces form a secure message encryption scheme.
Implementation Notes
- Select the mode, nonce handling, padding, and authentication behavior explicitly.
- Use library APIs that combine encryption and authentication when possible.
- Keep keys separate by purpose and rotate them according to system policy.
Common Pitfalls
- Using ECB mode for structured messages.
- Reusing a nonce with the same key in nonce-based modes.
- Confusing encryption with authentication.
Interactive Mechanism Walkthrough
Graph Frontier & Edge RelaxationShow a block passing through repeated transformation rounds.
Step 1 of 5: Expand the secret key into round keys
block-cipher-roundsNotes
AES is a block cipher primitive; the mode of operation determines how it is safely used on messages.
Sources (1)
What each reference supports for this entry.
NIST FIPS 197
DocumentationNIST Advanced Encryption Standard specification for AES-128, AES-192, and AES-256.
Open sourceExplore Next
Good next jumps from the relationship graph, ranked for useful discovery.
Alternative toChaCha20
Cryptography · Core
AES and ChaCha20 are symmetric encryption primitives with different implementation tradeoffs.
Compare with thisUsed byAES-CBC Mode
Cryptography · Core
AES-CBC Mode uses AES as a component or subroutine in its construction.
Compare with thisUsed byAES-CTR Mode
Cryptography · Core
AES-CTR Mode uses AES as a component or subroutine in its construction.
Compare with thisUsed byAES-GCM
Cryptography · Core
AES-GCM uses AES as a component or subroutine in its construction.
Compare with thisRelationships
View full relationship pageAlternative toChaCha20
AES and ChaCha20 are symmetric encryption primitives with different implementation tradeoffs.
Conceptual neighborFeistel Network
AES and Feistel networks are contrasting block-cipher construction styles.
Tags
CryptographySymmetric KeySecurity