AES Block Cipher Operation

Trace a 128-bit AES block through real round operations and learner-friendly visual checkpoints

An interactive AES round explorer with real SubBytes, ShiftRows, MixColumns, AddRoundKey, key-size presets, timeline controls, technical accuracy notes, and independent practice prompts.

animation security AES block cipher

AES Block Cipher Operation

Follow one 128-bit block as AES repeatedly substitutes bytes, shifts rows, mixes columns, and XORs round keys. The byte values are computed with the real AES operations for the selected test vector, while the interface slows the process down for inspection.

--Current round

--Active operation

--Bytes changed

--Key schedule

AES-128 known-answer block

One 16-byte block is shown as the AES 4 by 4 state matrix. Current checkpoint: initial AddRoundKey.

Before operation

After operation

--

--

Block checkpoints

Plaintext--

Round key--

Final ciphertext--

Round Controls

Start with the test vector, then switch key sizes or message profiles. Play advances through the actual AES checkpoint sequence.

Key size presets

Plaintext examples

Timeline checkpoint 1 / 40

Each checkpoint is one AES operation output: initial AddRoundKey, repeated round operations, then the final round without MixColumns.

AES Quick Reference

Block and state

• AES encrypts a 128-bit block.
• The block is arranged as 16 bytes in a 4 by 4 state matrix.
• All key sizes use the same 128-bit block size.

Round count

• AES-128 uses 10 rounds.
• AES-192 uses 12 rounds.
• AES-256 uses 14 rounds.

Normal round

• SubBytes changes each byte through the S-box.
• ShiftRows rotates row positions.
• MixColumns combines bytes within each column.
• AddRoundKey XORs a round key into the state.

Final round

• The final round still uses SubBytes.
• It still uses ShiftRows.
• It still uses AddRoundKey.
• It skips MixColumns by design.

Technical Accuracy Notes

Real transforms

The visualization computes the AES S-box, row shifts, MixColumns finite-field math, XOR round keys, and key expansion for AES-128, AES-192, and AES-256.

Teaching scope

This page is for learning the sequence and data movement. It is not constant-time code, does not implement modes such as GCM or CBC, and must not be used for production cryptography.

Security context

AES protects confidentiality only when used with an appropriate mode, nonce or IV handling, authentication, key management, and side-channel protections.

IoT relevance

Embedded devices often rely on hardware AES engines because software implementations can leak timing or power information and can be too slow for constrained nodes.

Practice Prompts

Trace a byte

Select SubBytes and note that a byte value changes without moving position. Then select ShiftRows and watch positions move without changing byte values.

Find diffusion

Step to MixColumns. Which columns change together, and why does this make one byte influence multiple later bytes?

Compare key sizes

Switch between AES-128, AES-192, and AES-256. What changes in the number of checkpoints, and what stays the same about the block and state?

Explain final round

Jump to the last round. Confirm that MixColumns is disabled, then describe which operation creates the final ciphertext.

DTLS Handshake Connect symmetric encryption to session establishment. Provisioning Security See where keys and device identity enter IoT onboarding. Credential Types Compare certificates, symmetric secrets, and rotation. Payload Builder Inspect the data that might be protected before transport.