zhguanw / sha256

Hardware implementation of the SHA-256 cryptographic hash function

sha256

Hardware implementation of the SHA-256 cryptographic hash function with support for both SHA-256 and SHA-224. The implementation is written in Verilog 2001 compliant code. The implementation includes the main core as well as wrappers that provides interfaces for simple integration.

This is a low area implementation that iterates over the rounds but there is no sharing of operations such as adders.

The hardware implementation is complemented by a functional model written in Python.

The core supports and has been included in the FuseSoC package manager.

Implementation status

The core has been completed for a long time and been used in several designs in ASICs as well as in FPGAs. The core is mature and ready for use. Minor changes are non-functional cleanups of code.

Implementation details

The sha256 design is divided into the following sections.

• src/rtl - RTL source files
• src/tb - Testbenches for the RTL files
• src/model/python - Functional model written in python
• doc - documentation (currently not done.)
• toolruns - Where tools are supposed to be run. Includes a Makefile for building and simulating the design using Icarus Verilog. There are also targets for linting the core using Verilator.

The actual core consists of the following files:

• sha256_core.v - The core itself with wide interfaces.
• sha256_w_mem.v - W message block memory and block expansion logic.
• sha256_k_constants.v - K constants ROM memory.

The top level entity is called sha256_core. This entity has wide interfaces (512 bit block input, 256 bit digest). In order to make it usable you probably want to wrap the core with a bus interface.

The provided top level wrapper, sha256.v provides a simple 32-bit memory like interface. The core (sha256_core) will sample all data inputs when given the init or next signal. the wrapper contains additional data registers. This allows you to load a new block while the core is processing the previous block.

The core supports both sha224 and sha256 modes. The default mode is sha256. The mode bit is located in the ADDR_CTRL API register and this means that when writing to this register to start processing a block, care must be taken to set the mode bit to the intended mode. This means that old code that for example simply wrote 0x01 to initiate SHA256 processing will now initiate SHA224 processing. Writing 0x05 will now initiate SHA256 processing.

Regarding SHA224, it is up to the user to only read seven, not eight words from the digest registers. The core will update the LSW too.

ASIC-results

Implementation in 40 nm low power standard cell process.

• Area: 14200 um2
• Combinational cells: 2344.9230
• Non-combinational cells: 2902.4856
• Clock frequency: 250 MHz

Fpga-results

Altera Cyclone FPGAs

Implementation results using Altera Quartus-II 13.1.

Cyclone IV E

• EP4CE6F17C6
• 3882 LEs
• 1813 registers
• 74 MHz
• 66 cycles latency

Cyclone IV GX

• EP4CGX22CF19C6
• 3773 LEs
• 1813 registers
• 76 MHz
• 66 cycles latency

Cyclone V

• 5CGXFC7C7F23C8
• 1469 ALMs
• 1813 registers
• 79 MHz
• 66 cycles latency

Xilinx FPGAs

Implementation results using ISE 14.7.

Spartan-6

• xc6slx45-3csg324
• 2012 LUTs
• 688 Slices
• 1929 regs
• 70 MHz
• 66 cycles latency

Implementation results using Vivado 2014.4.

Zynq-7030

• xc7z030fbg676-1
• 2308 LUTs
• 796 Slices
• 2116 regs
• 116 MHz
• 66 cycles latency

TODO

• Complete documentation.