Blowfish Wesley Wigham, Stephen Yingling, Chad Zawistowski - - PowerPoint PPT Presentation

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Blowfish Wesley Wigham, Stephen Yingling, Chad Zawistowski - - PowerPoint PPT Presentation

Jun 09, 2023 181 likes •333 views

Blowfish Wesley Wigham, Stephen Yingling, Chad Zawistowski Blowfish Block size of 64 bits Key size of 64 bits Feistel Network Complex P-array and S-box initialization Encrypts two entries to replace the next two 16

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SLIDE 1

Blowfish

Wesley Wigham, Stephen Yingling, Chad Zawistowski

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SLIDE 2

Blowfish

  • Block size of 64 bits
  • Key size of 64 bits
  • Feistel Network
  • Complex P-array and S-box

initialization

○ Encrypts two entries to replace the next two

  • 16 rounds
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SLIDE 3

Blowfish (cont.)

  • The function f splits
  • ne of the 32-bit

halves into 4 bytes

  • Each byte is run

through an S-box and then combined through addition/XOR

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SLIDE 4

Original Implementation

  • Used a for-loop to iterate through the rounds
  • The feistel function was not inlined, and was

called extremely often

  • Generating S-boxes was slow, but was only

performed once

  • Python’s pack and unpack methods were

used for converting between integers and byte arrays

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SLIDE 5

Original Call Stack

encrypt encrypt_block feistel pack unpack 1x 2x 16x 2x pack 1x

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SLIDE 6

Timetrial: Original

Encrypting the all-0 bytestring 2.5 million times (3 trials)

  • Average Running Time: 197.279 seconds
  • Total times spent in a selection of functions:

○ feistel = 82.666 secs ○ encrypt_block = 58.479 secs ○ pack = 31.230 secs ○ encrypt = 6.572 secs ○ unpack = 3.892 secs ○ generate S box = 0.002 secs

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SLIDE 7

Analysis

  • Spends a long time in encrypt_block

○ Mostly in ‘feistel’ ■ The ‘feistel’ function incurs quite a bit of

  • verhead, but is where most processing takes

place ○ Secondarily in ‘pack’ ■ python library call, converts bytearray to integer ■ ‘feistel’ also calls ‘pack’

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SLIDE 8

Optimized Implementation

  • Did in-place calculations of 2 rounds at once

to avoid left-right swapping overhead

  • Unrolled the rounds’ for-loop
  • Inlined the feistel function to remove calling
  • verhead
  • Within ‘encrypt_block’, replaced calls to

‘pack’ with inline bit operations

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SLIDE 9

Optimized Call Stack

encrypt encrypt_block 1x 1x 1x inline feistel 16x inline bitshift 2x pack inline pack

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SLIDE 10

Timetrial: Optimized

Encrypting the all-0 bytestring 2.5 million times (3 trials)

  • Average Running Time: 68.125 seconds
  • Total times spent in a selection of functions:

○ encrypt_block = 46.119 secs ○ encrypt = 6.561 secs ○ pack = 2.249 secs ○ generate S box = 0.012 secs ○ unpack = 0.001 secs

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SLIDE 11

Results of Changes

  • 2.94x faster overall

○ Switching to manual bitshift operations reduced time in pack by 29 seconds and in unpack by 3 seconds ○ Eliminated significant calling overhead by inlining the feistel function ○ Unrolled the for loop in encrypt_block and saved approximately 12 seconds

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SLIDE 12

Optimization Lessons

  • Python’s overhead for function calls

becomes significant over billions of calls

  • Python’s struct library is fairly inefficient for

combining bytearrays of known size into integers

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SLIDE 13

Future Work

  • Replace the remaining pack and unpack

functions with our own conversions

  • Unroll loops within the S box generation

function

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SLIDE 14

Questions?

?