aes

Verilog implementation of the symmetric block cipher AES (Advanced Encryption Standard) as specified in the NIST document FIPS 197.

Introduction

This implementation supports 128 and 256 bit keys. The implementation is iterative and process one 128 block at a time. Blocks are processed on a word level with 4 S-boxes in the data path. The S-boxes for encryption are shared with the key expansion and the core can thus not do key update in parallel with block processing.

The encipher and decipher block processing datapaths are separated and basically self contained given access to a set of round keys and a block. This makes it possible to hard wire either encipher or decipher and allow the build tools to optimize away the other functionality which will reduce the size to about 50%. For cipher modes such as CTR, GCM decryption in the AES core will never be used and thus the decipher block processing can be removed.

This is a fairly compact implementation. Further reduction could be achived by just having a single S-box. Similarly the performane can be increased by having 8 or even 16 S-boxes which would reduce the number of cycles to two cycles for each round.

Implementation results

The core has been implemented in Altera and Xilinx FPGA devices.

Altera Cyclone IV GX

• 7426 LEs
• 2994 Regs
• 96 MHz fmax
• 46 cycles/block

This means that we can do more than 2 Mblocks/s or 256 Mbps performance.

Removing the decipher module yields:

• 5497 LEs
• 2855 Regs
• 106 MHz fmax
• 46 cycles/block

Xilinx Spartan6LX-3

• 2576 slices
• 3000 regs
• 100 MHz
• 46 cycles/block

Xilinx Artix 7 200T-3

• 2298 slices
• 2989 regs
• 97 MHz
• 46 cycles/block

Status

(2016-11-20)

HEADSUP The API addresses for config and status registers has been switched. The reason for this is all other cores provided have status on 0x09. And any possible config on 0x0a. This change aligns the core for easier integration, but breaks designs that uses the old version.

The core VERSION string has been updated to reflect the API change.

The core NAME has also been updated. Precviously the NAME contained "-128", indicating that the core only supports 128 bit key length. But the core does in fact support both 128 and 256 bit key lengths.

(2016-09-06)

Updated implementation results with results from Xilinx Artix-7. There has also been done several minor fixes to shorten the code size, clarify the implementation etc. But the functionality of the core has not been altered. The core has been used in several designs.

(2014-11-28)

Top level simulation now passes all NISTs tests.

(2014-11-26)

Encryption and decryption now passes all NIST test cases on block level as well as core level. The Python model can do encryption but not decryption. The Python model contains separate tests for key generation, mixcolumns and inverse mixcolumns.

(2014-08-07)

Round key generation for both AES-128 and AES-256 now works when tested separately. Datapaths and core are yet to be debugged.

(2014-07-27)

Reworked the partitioning of block registers, round counters etc - basically a rather big change. The block processing is now pretty much self contained machines. Removed support for 192 bit keys.

(2014-04-26)

Most of the RTL completed but not yet debugged. The key expansion is still lacking. The architecture has been reworked several times, but this one looks promising.

(2014-03-19)

Several commits done up to this date. Halfway there. Changed name of repo to simply 'aes' to reflect that we will support at least both 128 and 256 bit keys. Possibly also 192 albeit nobody uses it (afaik).

(2014-02-21:

Initial commit. Nothing really here yet.