# AES :: Overview

## Project maintainers

## Details

Name: tiny_aes

Created: Oct 13, 2012

Updated: Dec 14, 2015

SVN Updated: Feb 21, 2013

SVN: Browse

Latest version: download

Statistics: View

## Other project properties

Category: Crypto core

Language: Verilog

Development status: Stable

Additional info:
Design done, FPGA proven, Specification done

WishBone compliant: No

WishBone version: n/a

License: Others

## Description

AES (Advanced Encryption Standard) is a specification published by

the American National Institute of Standards and Technology in 2001, as FIPS 197.[1]

AES describes a symmetric-key algorithm, in which the same key is used for

both encrypting and decrypting the data. The block size is restricted to 128 bits.

The key size can be 128, 192, or 256 bits. [1]

AES operates on a 4×4 matrix of bytes, called the state. Some rounds of transformation

converts the plaintext into the final cipher-text. The number of rounds is six plus

the key size divided by 32. One round reads the state into four 4-byte variables

y_0,y_1,y_2,y_3; transforms the variables; xor’s them by a 16-byte round key;

and puts the result into z_0,z_1,z_2,z_3.[3]

When targeting a variable-length plaintext, the plaintext must first be partitioned

into separate cipher blocks, and then be encrypted under some mode of operation,

generally using randomization based on an additional initialization vector.[4]

The cipher feedback (CFB) mode, output feedback (OFB) mode are specified in FIPS 81.

The counter (CTR) mode is specified by NIST in SP800-38A.[4] The advantage of these

modes is only using encryption algorithm for both encryption and decryption.

So the AES hardware price may be reduced by 50% (not need decryption hardware).

This project has implemented AES encryption algorithm.

This project provides three cores, doing AES-128, AES-192 and AES-256 encryption separately.

The cores can be used in cipher feedback (CFB) mode, output feedback (OFB) mode,

and counter (CTR) mode.

[1] Advanced Encryption Standard, http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

[2] J. Daemen and V. Rijmen. AES proposal: Rijndael. Original AES Submission to NIST, 1999.

[3] D. J. Bernstein and P. Schwabe. New AES software speed records. In INDOCRYPT 2008, volume 5365 of LNCS, pages 322-336, 2008.

[4] Block cipher modes of operation, http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation

## How to encrypt or decrypt a message

Suppose you use "aes_256" module, and the operation mode is CTR.

To encrypt something, let "aes_256.state" be a successive values of a "counter".

e.g, in clock cycle T+0, "aes_256.state == N+0", in clock cycle T+1, "aes_256.state == N+1", in clock cycle T+2, "aes_256.state == N+2".

Then "aes_256.out" is a binary sequence. Xor the binary sequence to the plain text to get the cipher text.

To decrypt something, let "aes_256.state" be a successive values of the SAME "counter".

Then "aes_256.out" is the SAME binary sequence. Xor the binary sequence to the cipher text to get the plain text.

If you feel it against intuition, please read http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

## Feature

- Pipeline architecture

- Ultra high speed

- Fully synchronous design

- Fully synthesize-able

- ONLY ONE clock domain in entire core

- NO latch

- All output signals are buffered

- Vendor-independent code

## Performance

The maximum frequency is 324.6 MHz (on Xilinx FPGA XC6VLX240T,

for all of AES-128, AES-192 and AES-256 implementation).

The core can encrypt 128 bit per clock cycle.

The throughput is 38.4 G bit /second (=4.8 G bytes/sec) if it is working with a 300 MHz clock.