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The core is completed and has been tested in several FPGAs designs.


This is a hardware implementation of the SipHash short-input PRF written in Verilog 2001.

The implementation is designed as a self contained core that performs the message block processing including initialization, compression and finalization operations. The core does not implement the functionality to divide a message into 64 bit message blocks.

The implementation supports user defined number of compression as well as finalization rounds. The core supports all combinations from SipHash-1-1 to SipHash-15-15.

The core is suitable as an application specific SipHash coprocessor offloading compact 8, 16 or 32 bit processors from hashing, PRF generation and Message Authentication Code (MAC) processing.

The project includes a testbench that verifies that the core generates the correct response to the testvectors in Appendix A of the SipHash paper [1]. The project also includes a simple Makefile for compiling the core using Icarus Verilog [3].

The core has been implemented in Altera and Xilinx FPGA devices. See Implementation notes below for more information.

This core is released as open source under a BSD license, see LICENSE.txt for more information.


The core accepts 64 bit blocks (mi) of a given message to process. Prior to processing a key dependent initalization. Initalization is done by setting the key port (k) and assering the (initalize) flag for at least one cycle and then deassert the flag.

There is default number of SipRounds for compression and finalization. The default values corresponds to the SipHash-2-4 described in the SipHash paper.

Processing a message block is done by assigning the block to the message block port (mi) and asserting the (compress) flag.

Note that the core does not know the length of the message and does not perform final padding. The user of the core is expected to perform padding including setting length of the message in the final block.

After all blocks in the message has been processed the processing is completed by asserting the (finalize) flag for one cycle.

The core will assert the (siphash_word_valid) flag when the new SipHash word for the message is ready.

The core will only accept new commands (initialize, compress, finalize) when the (ready) flag is asserted.

Implementation notes

The core is implemented using the Verilog 2001 hardware description language. The core uses synchronous reset for all registers and all registers are equipped with write enable. The core should integrate and build cleanly into any standard FPGA project.

The core implements the SipRound function with four 64 bit adders capable of performing operations in parallel. A single SipRound operation takes one cycle to perform.

Total latency for processing a message that consists of a single 64 bit block using SipHash-2-4 is:

  • 1 cycle for initialization
  • 1 + 2 + 1 = 4 cycles for compression
  • 4 + 1 = 5 cycles for finalization
  • 1 + 4 = 5 cycles more for long mode

In total: 10 cycles or 1.25 cycles/Byte. For long mode 15 cycles or 1.875 cycles/Byte. For long messages, the latency is asymptotically 0.5 cycles/Byte.

The repo contains both the core itself (siphash_core.v) and a top level wrapper (siphash.v). The wrapper provides a simple 32-bit interface for the core for easy integration into a system on chip.

Implementation results

Altera FPGAs

Altera Cyclone V

  • Specific device: 5CGXFC7D6F31C7
  • ALMs: 657
  • Regs: 867
  • No memory blocks, DSPs allocated
  • 116 MHz max, slow 85c model

Altera Cyclone IV E

  • Specific device: EP4CE6F17C6
  • LEs: 1576
  • Regs: 794
  • No memory blocks, DSPs allocated
  • 101 MHz max, slow 85c model

Xilinx FPGAs


  • xc6slx75-3fgg676
  • 1235 LUTs
  • 345 Slices
  • 793 regs
  • 114 MHz


  • xc7a200t-3fbg484
  • 998 LUTs
  • 432 Slices
  • 789 regs
  • 173 MHz


[1] J-P. Aumasson, D. J. Bernstein. SipHash: a fast short-input PRF.

[3] Icarus Verilog


Hardware implementation of the SipHash short-inout PRF




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