Blowfish

What is Blowfish?

  • Blowfish is a symmetric-key block cipher created by Bruce Schneier in 1993.

  • It operates on 64-bit blocks and supports variable key lengths from 32 to 448 bits.

  • Designed as a fast, unpatented, and secure alternative to DES—especially well-suited for software implementations.

Why is Blowfish useful?

  • Fast and lightweight – Optimized for 32-bit CPUs and embedded environments

  • Flexible key size – Customizable security strength (32–448 bits)

  • Free to use – Unpatented and royalty-free

  • Security – Strong resistance to known attacks

  • Note – Its 64-bit block size is now a limitation for encrypting large volumes of data

How it works

  • Key expansion – The key is used to generate 18 subkeys and 4 S-boxes

  • Encryption – Uses a 16-round Feistel network on 64-bit blocks (split into 32-bit halves), involving substitution, XOR, and permutation

  • Transmission/Storage – Ciphertext is safely transmitted or stored

  • Decryption – Same process in reverse, applying the subkeys in opposite order

Where is Blowfish used?

  • File encryption tools – e.g., GnuPG, early TrueCrypt

  • Password hashing – bcrypt is based on Blowfish

  • Embedded devices – Efficient for low-power environments

  • VPNs and secure tunnels – In legacy implementations

  • Legacy systems – Still in use where AES migration hasn’t occurred

Which OSI layer does this protocol belong to?

  • Presentation Layer (Layer 6)

  • Handles encryption and decryption before data reaches the application

  • Blowfish formats and protects data to ensure confidentiality and secure representation

Topics in this section,

  • In this section, you are going to learn

  • Terminology

  • Version Info

Blowfish Version

Blowfish Number

Year

Core Idea / Contribution

Blowfish Cipher (Original)

N/A (Published in Applied Cryptography)

1993

Introduced by Bruce Schneier as a fast, free, and unpatented alternative to DES. Uses a 16-round Feistel network, key-dependent S-boxes, and supports variable key lengths (32448 bits).

Blowfish in Password Hashing

bcrypt (based on Blowfish)

~1999

Adapted for secure password hashing. bcrypt adds a work factor (cost) to slow down brute-force attacks.

Blowfish in Open Source Tools

Various (e.g., OpenSSH, GnuPG)

1990s2000s

Widely adopted in open-source encryption tools and libraries before AES became the standard.

Blowfish in Embedded Systems

N/A

Ongoing

Still used in embedded and legacy systems due to its small footprint and efficiency.

  • Setup

  • Setup

Blowfish key Setup Packet

S.No

Protocol Packets

Description

Size(Bytes)

1

Blowfish Key Setup Packet

Initializes the cipher with a secret key, generating subkeys and S-boxes.

~4,200 (internal setup)

Secret Key

User-defined key for encryption/decryption.

456

Subkeys (P-array)

18 32-bit subkeys used in encryption rounds.

72

S-boxes

Four 256-entry substitution boxes (32-bit each).

4,096

Blowfish Encryption Packet

S.No

Protocol Packets

Description

Size(Bytes)

2

Blowfish Encryption Packet

Encrypts a 64-bit block of plaintext using the Feistel network.

8 to 16

Plaintext Block

Original data to be encrypted.

8

Ciphertext Block

Encrypted output after 16 rounds.

8

IV (if in CBC mode)

Initialization vector for block cipher modes.

8 (optional)

Blowfish Decryption Packet

S.No

Protocol Packets

Description

Size(Bytes)

3

Blowfish Decryption Packet

Decrypts a 64-bit block of ciphertext using reversed subkeys.

8 to 16

Ciphertext Block

Encrypted data to be decrypted.

8

Plaintext Block

Recovered original data.

8

IV (if in CBC mode)

Required for decryption in certain modes.

8 (optional)

Blowfish - Use Cases

S.no

Use Case

Description

1

File Encryption

Used in tools like GnuPG and older versions of TrueCrypt for encrypting files.

2

Password Hashing

Basis for the bcrypt algorithm, widely used for securely storing passwords.

3

Embedded Systems

Preferred in low-resource environments due to its small size and efficiency.

4

VPNs and Secure Tunnels

Occasionally used in older VPN implementations for encrypting data streams.

5

Legacy Applications

Still found in older systems and software where AES has not been adopted.

6

Open Source Tools

Implemented in various open-source cryptographic libraries and utilities.

S.no

Feature

Description

1

Symmetric Block Cipher

Uses the same key for both encryption and decryption; operates on 64-bit blocks.

2

Variable Key Length

Supports key sizes from 32 to 448 bits, allowing flexible security levels.

3

16-Round Feistel Network

Encryption is performed through 16 rounds of substitution and permutation.

4

Key-Dependent S-boxes

S-boxes are generated from the key, making each encryption unique.

5

Fast in Software

Optimized for speed on 32-bit processors and software-based implementations.

6

No Licensing Required

Freely available for use; not patented or restricted.

7

Secure Design

Resistant to known attacks like differential and linear cryptanalysis.

8

Lightweight Implementation

Suitable for embedded systems and low-resource environments.

9

Legacy Compatibility

Still used in older systems and applications where AES is not adopted.

10

Basis for bcrypt

Forms the core of the bcrypt password hashing algorithm used in secure systems.

Symmetric Block Cipher - Testcases

#

Test Case

Description

Expected Result

1

Encrypt on Windows

Run Blowfish encryption on Windows OS

Encryption successful

2

Decrypt on Windows

Run Blowfish decryption on Windows OS

Decryption successful

3

Encrypt on Linux

Run Blowfish encryption on Linux OS

Encryption successful

4

Decrypt on Linux

Run Blowfish decryption on Linux OS

Decryption successful

5

Encrypt on macOS

Run Blowfish encryption on macOS

Encryption successful

6

Decrypt on macOS

Run Blowfish decryption on macOS

Decryption successful

7

Encrypt on Android

Run Blowfish in Android app

Encryption successful

8

Decrypt on Android

Run Blowfish in Android app

Decryption successful

9

Encrypt on iOS

Run Blowfish in iOS app

Encryption successful

10

Decrypt on iOS

Run Blowfish in iOS app

Decryption successful

11

Encrypt on Raspberry Pi

Run Blowfish on ARM CPU

Encryption successful

12

Decrypt on Raspberry Pi

Run Blowfish on ARM CPU

Decryption successful

13

Encrypt with Python

Use PyCryptodome Blowfish

Encryption successful

14

Decrypt with Python

Use PyCryptodome Blowfish

Decryption successful

15

Encrypt with Java

Use BouncyCastle Blowfish

Encryption successful

16

Decrypt with Java

Use BouncyCastle Blowfish

Decryption successful

17

Encrypt with C++

Use OpenSSL Blowfish

Encryption successful

18

Decrypt with C++

Use OpenSSL Blowfish

Decryption successful

19

Encrypt with Go

Use Go crypto Blowfish

Encryption successful

20

Decrypt with Go

Use Go crypto Blowfish

Decryption successful

21

Encrypt with Node.js

Use crypto module

Encryption successful

22

Decrypt with Node.js

Use crypto module

Decryption successful

23

Encrypt with .NET

Use System.Security.Cryptography

Encryption successful

24

Decrypt with .NET

Use System.Security.Cryptography

Decryption successful

25

Encrypt with Rust

Use RustCrypto Blowfish

Encryption successful

26

Decrypt with Rust

Use RustCrypto Blowfish

Decryption successful

27

Encrypt with CLI Tool

Use OpenSSL CLI

Encryption successful

28

Decrypt with CLI Tool

Use OpenSSL CLI

Decryption successful

29

Encrypt in Docker

Run Blowfish in container

Encryption successful

30

Decrypt in Docker

Run Blowfish in container

Decryption successful

31

Encrypt in VM

Run Blowfish in virtual machine

Encryption successful

32

Decrypt in VM

Run Blowfish in virtual machine

Decryption successful

33

Encrypt in WebAssembly

Run Blowfish in browser

Encryption successful

34

Decrypt in WebAssembly

Run Blowfish in browser

Decryption successful

35

Encrypt on Smartwatch

Run Blowfish on wearable OS

Encryption successful

36

Decrypt on Smartwatch

Run Blowfish on wearable OS

Decryption successful

37

Encrypt on IoT Device

Run Blowfish on microcontroller

Encryption successful

38

Decrypt on IoT Device

Run Blowfish on microcontroller

Decryption successful

39

Encrypt on POS Terminal

Run Blowfish on payment device

Encryption successful

40

Decrypt on POS Terminal

Run Blowfish on payment device

Decryption successful

41

Encrypt on Smart TV

Run Blowfish on Android TV

Encryption successful

42

Decrypt on Smart TV

Run Blowfish on Android TV

Decryption successful

43

Encrypt on Automotive OS

Run Blowfish in car system

Encryption successful

44

Decrypt on Automotive OS

Run Blowfish in car system

Decryption successful

45

Encrypt on ARM64

Run Blowfish on 64-bit ARM

Encryption successful

46

Decrypt on ARM64

Run Blowfish on 64-bit ARM

Decryption successful

47

Encrypt on x86_64

Run Blowfish on Intel/AMD

Encryption successful

48

Decrypt on x86_64

Run Blowfish on Intel/AMD

Decryption successful

49

Encrypt with same key

Encrypt using key K1

Ciphertext generated

50

Decrypt with same key

Decrypt using key K1

Original plaintext restored

Variable Key Length - Testcases

#

Test Case

Description

Expected Result

1

Encrypt with 32-bit key

Use 4-byte key

Encryption successful

2

Encrypt with 64-bit key

Use 8-byte key

Encryption successful

3

Encrypt with 128-bit key

Use 16-byte key

Encryption successful

4

Encrypt with 192-bit key

Use 24-byte key

Encryption successful

5

Encrypt with 256-bit key

Use 32-byte key

Encryption successful

6

Encrypt with 320-bit key

Use 40-byte key

Encryption successful

7

Encrypt with 384-bit key

Use 48-byte key

Encryption successful

8

Encrypt with 448-bit key

Use 56-byte key

Encryption successful

9

Decrypt with 32-bit key

Use same 4-byte key

Decryption successful

10

Decrypt with 448-bit key

Use same 56-byte key

Decryption successful

11

Encrypt with invalid key (16 bits)

Use 2-byte key

Error: Key too short

12

Encrypt with invalid key (512 bits)

Use 64-byte key

Error: Key too long

13

Encrypt with random 40-bit key

Use 5-byte key

Encryption successful

14

Encrypt with random 72-bit key

Use 9-byte key

Encryption successful

15

Encrypt with random 104-bit key

Use 13-byte key

Encryption successful

16

Encrypt with random 200-bit key

Use 25-byte key

Encryption successful

17

Encrypt with random 300-bit key

Use 37.5-byte key (rounded)

Encryption successful

18

Encrypt with random 448-bit key

Use 56-byte key

Encryption successful

19

Encrypt with all-zero key

Use 32-byte key of zeros

Encryption successful

20

Encrypt with all-ones key

Use 32-byte key of 0xFF

Encryption successful

21

Encrypt with alternating bits

Use 32-byte key of 0xAA55 pattern

Encryption successful

22

Encrypt with ASCII key

Use “MySecretKey123”

Encryption successful

23

Encrypt with Unicode key

Use UTF-8 encoded key

Encryption successful

24

Encrypt with binary key

Use raw binary data

Encryption successful

25

Encrypt with hex key

Use hex-encoded key

Encryption successful

26

Encrypt with base64 key

Decode and use key

Encryption successful

27

Encrypt with password-derived key

Use PBKDF2 to derive key

Encryption successful

28

Encrypt with key from file

Load key from external file

Encryption successful

29

Encrypt with key from environment variable

Load key securely

Encryption successful

30

Encrypt with key from hardware module

Use HSM

Encryption successful

31

Encrypt with key from TPM

Use Trusted Platform Module

Encryption successful

32

Encrypt with key from secure enclave

Use Apple Secure Enclave

Encryption successful

33

Encrypt with key from Android Keystore

Use Android system key

Encryption successful

34

Encrypt with key from AWS KMS

Use cloud key management

Encryption successful

35

Encrypt with key from Azure Key Vault

Use cloud key management

Encryption successful

36

Encrypt with key from GCP KMS

Use cloud key management

Encryption successful

37

Encrypt with key rotation

Change key every 10 minutes

Encryption successful

38

Encrypt with session key

Generate per-session key

Encryption successful

39

Encrypt with ephemeral key

Use temporary key

Encryption successful

40

Encrypt with static key

Use fixed key

Encryption successful

41

Encrypt with user-defined key length

Accept user input (e.g., 160 bits)

Encryption successful

42

Encrypt with max key length on embedded device

Use 448-bit key on microcontroller

Encryption successful

43

Encrypt with min key length on embedded device

Use 32-bit key on microcontroller

Encryption successful

44

Encrypt with 448-bit key on Windows

Full key length support

Encryption successful

45

Encrypt with 448-bit key on Linux

Full key length support

Encryption successful

46

Encrypt with 448-bit key on macOS

Full key length support

Encryption successful

47

Encrypt with 448-bit key in browser (WASM)

Full key length support

Encryption successful

48

Encrypt with 448-bit key in Docker

Full key length support

Encryption successful

49

Encrypt with 448-bit key in cloud function

Full key length support

Encryption successful

50

Encrypt and decrypt with same variable-length key

Ensure round-trip correctness

Plaintext restored

16-Round Feistel Network - Testcases

#

Test Case

Description

Expected Result

1

Validate 16 rounds

Ensure exactly 16 rounds are executed

16 rounds confirmed

2

Round 1 substitution

Check S-box substitution in round 1

Substitution successful

3

Round 1 permutation

Check permutation in round 1

Permutation successful

4

Round 8 substitution

Check S-box substitution in round 8

Substitution successful

5

Round 8 permutation

Check permutation in round 8

Permutation successful

6

Round 16 substitution

Check S-box substitution in final round

Substitution successful

7

Round 16 permutation

Check permutation in final round

Permutation successful

8

Round key usage

Verify unique subkey used in each round

16 unique subkeys used

9

Round function consistency

Ensure round function is consistent

Output matches expected

10

Round output chaining

Output of one round is input to next

Chaining verified

11

Encrypt with known input

Use test vector with known output

Output matches expected

12

Decrypt with known input

Use test vector with known ciphertext

Plaintext restored

13

Round-by-round trace

Log intermediate values for each round

All 16 rounds logged

14

Round 1 input/output

Capture input/output of round 1

Values match expected

15

Round 16 input/output

Capture input/output of round 16

Values match expected

16

Round function reversibility

Ensure decryption reverses encryption

Plaintext restored

17

Round key derivation

Validate P-array usage in rounds

Keys derived correctly

18

Round timing

Measure time per round

Consistent timing

19

Round integrity

Tamper with round 5 output

Decryption fails

20

Round skipping

Skip round 10

Output incorrect

21

Round duplication

Duplicate round 3

Output incorrect

22

Round order change

Swap round 4 and 5

Output incorrect

23

Round key reuse

Use same key for all rounds

Output incorrect

24

Round function mutation

Modify round function logic

Output incorrect

25

Round function isolation

Test round function independently

Output matches expected

26

Round function with zero input

Input all zeros

Output non-zero

27

Round function with max input

Input all 1s

Output non-zero

28

Round function with alternating bits

Input 0xAA55 pattern

Output valid

29

Round function with random input

Random 64-bit input

Output valid

30

Round function with fixed key

Use static key

Output consistent

31

Round function with variable key

Use different keys

Output varies

32

Round function on embedded device

Run on microcontroller

All rounds executed

33

Round function on cloud

Run in cloud function

All rounds executed

34

Round function on browser

Run in WebAssembly

All rounds executed

35

Round function on mobile

Run on Android/iOS

All rounds executed

36

Round function on legacy system

Run on old OS

All rounds executed

37

Round function with logging

Enable debug logs

All rounds logged

38

Round function with fault injection

Inject fault in round 7

Output incorrect

39

Round function with padding

Encrypt padded input

Padding handled

40

Round function with block chaining

Use CBC mode

All rounds executed

41

Round function with ECB mode

Use ECB mode

All rounds executed

42

Round function with CFB mode

Use CFB mode

All rounds executed

43

Round function with OFB mode

Use OFB mode

All rounds executed

44

Round function with CTR mode

Use CTR mode

All rounds executed

45

Round function with corrupted key

Use wrong key

Decryption fails

46

Round function with corrupted ciphertext

Modify ciphertext

Decryption fails

47

Round function with corrupted plaintext

Modify plaintext

Ciphertext changes

48

Round function with short input

Less than 64 bits

Error or padding applied

49

Round function with long input

More than 64 bits

Split into blocks

50

Round function full cycle

Encrypt and decrypt with 16 rounds

Plaintext restored

Key-Dependent S-boxes - Testcases

#

Test Case

Description

Expected Result

1

Generate S-box with key A

Use key “Alpha123”

Unique S-box generated

2

Generate S-box with key B

Use key “Beta456”

Different S-box from key A

3

Same key, same S-box

Use key “Gamma789” twice

Identical S-boxes

4

Different keys, same plaintext

Encrypt with key A and B

Different ciphertexts

5

Same key, same plaintext

Encrypt twice

Same ciphertext

6

Modify 1 bit in key

Slight change in S-box

Ciphertext changes

7

Use all-zero key

Generate S-box

Valid S-box generated

8

Use all-one key

Generate S-box

Valid S-box generated

9

Use alternating bits key

Generate S-box

Unique S-box generated

10

Use random key

Generate S-box

Unique S-box generated

11

Log S-box values

Output S-box after key setup

S-box values printed

12

Compare S-boxes

Use two different keys

S-boxes differ

13

S-box size check

Ensure 4 S-boxes of 256 entries

Size = 4 256

14

S-box initialization

Check initial values before keying

Matches Blowfish spec

15

S-box after keying

Check values after key expansion

Values changed

16

S-box uniqueness

Encrypt same plaintext with 10 keys

10 different ciphertexts

17

S-box collision test

Use similar keys

No S-box collisions

18

S-box entropy test

Measure randomness

High entropy

19

S-box with short key

Use 32-bit key

Valid S-box generated

20

S-box with long key

Use 448-bit key

Valid S-box generated

21

S-box with Unicode key

Use UTF-8 key

Valid S-box generated

22

S-box with binary key

Use raw binary key

Valid S-box generated

23

S-box with hex key

Use hex-encoded key

Valid S-box generated

24

S-box with base64 key

Decode and use

Valid S-box generated

25

S-box with password-derived key

Use PBKDF2

Valid S-box generated

26

S-box regeneration

Reinitialize with new key

S-box updated

27

S-box persistence

Save and reload S-box

Values preserved

28

S-box tampering

Modify S-box manually

Decryption fails

29

S-box export

Export S-box to file

File saved

30

S-box import

Load S-box from file

S-box loaded

31

S-box in embedded system

Generate on microcontroller

Successful

32

S-box in cloud function

Generate in serverless env

Successful

33

S-box in browser

Generate in WebAssembly

Successful

34

S-box in mobile app

Generate on Android/iOS

Successful

35

S-box in Docker

Generate in container

Successful

36

S-box in VM

Generate in virtual machine

Successful

37

S-box in legacy system

Generate on old OS

Successful

38

S-box with corrupted key

Use invalid key

Error or fallback

39

S-box with empty key

Use zero-length key

Error or default

40

S-box with max key

Use 448-bit key

Full S-box generated

41

S-box with min key

Use 32-bit key

Minimal S-box generated

42

S-box with key rotation

Change key periodically

S-box updated

43

S-box with session key

Generate per session

Unique S-box per session

44

S-box with static key

Use fixed key

Same S-box every time

45

S-box with ephemeral key

Use temporary key

S-box discarded after use

46

S-box with hardware key

Use HSM-derived key

S-box generated

47

S-box with TPM key

Use TPM module

S-box generated

48

S-box with secure enclave

Use Apple Secure Enclave

S-box generated

49

S-box with Android Keystore

Use system key

S-box generated

50

S-box round-trip test

Encrypt and decrypt with same key

Plaintext restored

Fast in Software - Testcases

#

Test Case

Description

Expected Result

1

Encrypt on 32-bit CPU

Run Blowfish on 32-bit Intel

Fast encryption

2

Encrypt on 64-bit CPU

Run Blowfish on 64-bit AMD

Fast encryption

3

Encrypt on ARMv7

Run Blowfish on 32-bit ARM

Fast encryption

4

Encrypt on ARM64

Run Blowfish on 64-bit ARM

Fast encryption

5

Encrypt on Raspberry Pi

Run Blowfish on Pi 3

Fast encryption

6

Encrypt on Android

Run Blowfish in app

Fast encryption

7

Encrypt on iOS

Run Blowfish in app

Fast encryption

8

Encrypt on Windows

Run Blowfish in desktop app

Fast encryption

9

Encrypt on Linux

Run Blowfish in CLI tool

Fast encryption

10

Encrypt on macOS

Run Blowfish in GUI app

Fast encryption

11

Encrypt in Docker

Run Blowfish in container

Fast encryption

12

Encrypt in VM

Run Blowfish in virtual machine

Fast encryption

13

Encrypt in WebAssembly

Run Blowfish in browser

Fast encryption

14

Encrypt in Python

Use PyCryptodome

Fast execution

15

Encrypt in Java

Use BouncyCastle

Fast execution

16

Encrypt in C++

Use OpenSSL

Fast execution

17

Encrypt in Go

Use crypto/blowfish

Fast execution

18

Encrypt in Rust

Use RustCrypto

Fast execution

19

Encrypt in Node.js

Use crypto module

Fast execution

20

Encrypt in .NET

Use System.Security

Fast execution

21

Encrypt 1KB file

Measure time

< 1 ms

22

Encrypt 10KB file

Measure time

< 5 ms

23

Encrypt 100KB file

Measure time

< 50 ms

24

Encrypt 1MB file

Measure time

< 500 ms

25

Encrypt 10MB file

Measure time

< 5 s

26

Encrypt 100MB file

Measure time

< 30 s

27

Encrypt with 32-bit key

Measure speed

Fast

28

Encrypt with 448-bit key

Measure speed

Slightly slower

29

Encrypt with CBC mode

Measure speed

Fast

30

Encrypt with ECB mode

Measure speed

Fast

31

Encrypt with CFB mode

Measure speed

Fast

32

Encrypt with OFB mode

Measure speed

Fast

33

Encrypt with CTR mode

Measure speed

Fast

34

Encrypt with padding

Add PKCS#5 padding

Fast

35

Encrypt without padding

Input is 64-bit aligned

Fast

36

Encrypt in batch

Encrypt 1000 blocks

Fast

37

Encrypt in stream

Encrypt block-by-block

Fast

38

Encrypt in parallel

Use multithreading

Speedup observed

39

Encrypt with SIMD

Use vector instructions

Speedup observed

40

Encrypt with JIT

Use JIT-compiled language

Fast

41

Encrypt with interpreter

Use Python

Acceptable speed

42

Encrypt on low-end CPU

Use old Intel Pentium

Still fast

43

Encrypt on high-end CPU

Use modern Ryzen

Very fast

44

Encrypt on embedded OS

Use RTOS

Fast

45

Encrypt on real-time system

Use Blowfish in PLC

Fast

46

Encrypt on IoT device

Use ESP32

Fast

47

Encrypt on smartwatch

Use Wear OS

Fast

48

Encrypt on smart TV

Use Android TV

Fast

49

Encrypt on automotive OS

Use QNX or Android Auto

Fast

50

Encrypt and decrypt cycle

Measure total time

Fast round-trip

No Licensing Required - Testcases

#

Test Case

Description

Expected Result

1

Use in open-source project

Include Blowfish in GitHub repo

No license conflict

2

Use in commercial software

Integrate Blowfish in paid app

No licensing fees

3

Use in academic research

Implement in thesis project

No restrictions

4

Use in government software

Deploy in public sector app

No legal issues

5

Use in embedded systems

Flash Blowfish to firmware

No IP concerns

6

Use in mobile app

Add Blowfish to Android/iOS app

No license required

7

Use in cloud service

Encrypt data in AWS Lambda

No licensing needed

8

Use in desktop software

Add Blowfish to Windows app

No license required

9

Use in IoT device

Implement in smart sensor

No licensing issues

10

Use in blockchain

Add Blowfish to smart contract

No IP conflict

11

Use in VPN software

Encrypt traffic with Blowfish

No license required

12

Use in messaging app

Secure messages with Blowfish

No licensing needed

13

Use in file encryption tool

Encrypt files locally

No license required

14

Use in password manager

Encrypt vault with Blowfish

No licensing needed

15

Use in academic paper

Publish Blowfish-based algorithm

No copyright issues

16

Use in educational tool

Teach cryptography with Blowfish

No restrictions

17

Use in hardware wallet

Implement Blowfish in firmware

No licensing needed

18

Use in router firmware

Add Blowfish to OpenWRT

No license conflict

19

Use in NAS device

Encrypt storage with Blowfish

No licensing needed

20

Use in smart home hub

Secure communication

No IP issues

21

Use in game engine

Encrypt assets with Blowfish

No licensing required

22

Use in browser extension

Encrypt data in extension

No license needed

23

Use in CLI tool

Add Blowfish to command-line app

No restrictions

24

Use in server backend

Encrypt API data

No licensing required

25

Use in frontend JS

Implement Blowfish in browser

No license needed

26

Use in Python script

Use PyCryptodome Blowfish

No license required

27

Use in Java app

Use BouncyCastle Blowfish

No licensing issues

28

Use in C++ app

Use OpenSSL Blowfish

No license conflict

29

Use in Go app

Use crypto/blowfish

No licensing needed

30

Use in Rust app

Use RustCrypto Blowfish

No restrictions

31

Use in .NET app

Use System.Security Blowfish

No license required

32

Use in Node.js app

Use crypto module

No licensing needed

33

Use in Flutter app

Add Blowfish plugin

No license required

34

Use in React Native app

Add Blowfish module

No licensing issues

35

Use in Xamarin app

Add Blowfish encryption

No license required

36

Use in Unity game

Encrypt data with Blowfish

No licensing needed

37

Use in Arduino project

Add Blowfish to sketch

No restrictions

38

Use in ESP32 firmware

Add Blowfish to embedded code

No licensing needed

39

Use in FPGA

Implement Blowfish in HDL

No IP issues

40

Use in ASIC

Hardwire Blowfish logic

No licensing required

41

Use in academic course

Teach Blowfish in class

No license needed

42

Use in cryptography book

Include Blowfish examples

No copyright issues

43

Use in online tutorial

Publish Blowfish guide

No restrictions

44

Use in YouTube video

Explain Blowfish algorithm

No licensing needed

45

Use in podcast

Discuss Blowfish freely

No IP concerns

46

Use in whitepaper

Propose Blowfish-based system

No licensing required

47

Use in patent filing

Reference Blowfish as prior art

No infringement

48

Use in security audit

Analyze Blowfish implementation

No license needed

49

Use in compliance report

Document Blowfish usage

No legal issues

50

Use in startup product

Launch with Blowfish encryption

No licensing fees

Security Design - Testcases

#

Test Case

Description

Expected Result

1

Differential cryptanalysis test

Apply input pairs with known differences

No statistical bias

2

Linear cryptanalysis test

Attempt linear approximations

No exploitable correlation

3

Avalanche effect test

Flip 1 bit in plaintext

>50% bits change in ciphertext

4

Avalanche effect on key

Flip 1 bit in key

>50% bits change in ciphertext

5

Key sensitivity test

Use two similar keys

Ciphertexts differ significantly

6

Plaintext sensitivity test

Use two similar plaintexts

Ciphertexts differ significantly

7

Known plaintext attack

Encrypt known plaintext

Key remains secure

8

Chosen plaintext attack

Encrypt attacker-chosen input

No key leakage

9

Chosen ciphertext attack

Decrypt attacker-chosen input

No key leakage

10

Brute-force attack

Try all key combinations

Computationally infeasible

11

Meet-in-the-middle attack

Attempt on 2-round Blowfish

Not applicable to full 16 rounds

12

Replay attack

Reuse ciphertext

No effect without context

13

Timing attack

Measure encryption time

No key-dependent timing

14

Power analysis attack

Monitor power usage

No direct leakage

15

Fault injection attack

Inject bit errors

No key recovery

16

Side-channel attack

Monitor CPU cache

No exploitable patterns

17

S-box analysis

Analyze key-dependent S-boxes

No predictable structure

18

Round function analysis

Analyze Feistel rounds

No linearity found

19

Key schedule analysis

Analyze P-array generation

No weaknesses found

20

Differential trail depth

Analyze propagation

High diffusion

21

Linear trail depth

Analyze linear approximations

Low correlation

22

Ciphertext-only attack

Analyze ciphertexts

No plaintext recovery

23

Frequency analysis

Analyze ciphertext frequency

No patterns found

24

Statistical analysis

Analyze ciphertext distribution

Uniform distribution

25

Entropy test

Measure ciphertext entropy

High entropy

26

Randomness test

Use NIST test suite

Passes all tests

27

Collision resistance

Encrypt different inputs

No collisions

28

Key collision test

Use different keys

No ciphertext collisions

29

Block collision test

Encrypt same block with different keys

Different ciphertexts

30

Resistance to algebraic attacks

Attempt algebraic modeling

No success

31

Resistance to interpolation attacks

Attempt polynomial interpolation

No success

32

Resistance to integral attacks

Analyze byte sums

No patterns found

33

Resistance to boomerang attack

Attempt boomerang differential

No success

34

Resistance to truncated differential

Use partial differences

No advantage gained

35

Resistance to impossible differential

Use impossible pairs

No key leakage

36

Resistance to related-key attack

Use related keys

No correlation in output

37

Resistance to biclique attack

Attempt biclique optimization

No speedup

38

Resistance to slide attack

Attempt sliding keys

Not applicable

39

Resistance to key clustering

Use similar keys

No clustering observed

40

Resistance to weak keys

Test known weak key patterns

No vulnerabilities

41

Resistance to backdoor insertion

Analyze implementation

No hidden behavior

42

Resistance to padding oracle attack

Use proper padding

No oracle behavior

43

Resistance to format-preserving attack

Encrypt structured data

Structure not preserved

44

Resistance to plaintext recovery

Encrypt known format

No recovery possible

45

Resistance to ciphertext manipulation

Modify ciphertext

Decryption fails

46

Resistance to replay in CBC mode

Use IVs properly

No reuse vulnerability

47

Resistance to IV reuse

Use unique IVs

No leakage

48

Resistance to downgrade attacks

Use full 16 rounds

No reduced-round fallback

49

Resistance to protocol misuse

Use in secure protocol

No misuse vulnerability

50

Resistance to hybrid attacks

Combine multiple methods

No key recovery

Lightweight Implementation - Testcases

#

Test Case

Description

Expected Result

1

Run on 8-bit microcontroller

Implement Blowfish on AVR

Successful encryption

2

Run on 16-bit microcontroller

Use MSP430

Successful encryption

3

Run on 32-bit microcontroller

Use STM32

Successful encryption

4

Run on Arduino Uno

Limited RAM and flash

Encryption successful

5

Run on ESP8266

Wi-Fi microcontroller

Encryption successful

6

Run on ESP32

Dual-core MCU

Encryption successful

7

Run on Raspberry Pi Pico

RP2040 chip

Encryption successful

8

Run on ARM Cortex-M0

Ultra-low power

Encryption successful

9

Run on ARM Cortex-M4

DSP-enabled MCU

Encryption successful

10

Run on TI LaunchPad

Low-cost dev board

Encryption successful

11

Run on Atmel SAMD21

32-bit ARM MCU

Encryption successful

12

Run on Nordic nRF52

BLE-enabled MCU

Encryption successful

13

Run on STM32F103

Blue Pill board

Encryption successful

14

Run on Teensy 4.0

High-performance MCU

Encryption successful

15

Run on low-RAM device

<2KB RAM

Encryption successful

16

Run on low-flash device

<32KB flash

Encryption successful

17

Compile with GCC

Use minimal flags

Small binary size

18

Compile with Clang

Optimize for size

Small binary size

19

Compile with -Os flag

Optimize for space

Reduced binary size

20

Compile with -O2 flag

Optimize for speed

Fast execution

21

Use in FreeRTOS

Run Blowfish task

Task runs successfully

22

Use in Zephyr RTOS

Encrypt in thread

Encryption successful

23

Use in bare-metal C

No OS environment

Encryption successful

24

Use in embedded Linux

Run on OpenWRT

Encryption successful

25

Use in TinyGo

Compile for microcontroller

Encryption successful

26

Use in MicroPython

Run on ESP32

Encryption successful

27

Use in CircuitPython

Run on Adafruit board

Encryption successful

28

Use in embedded Rust

Run on Cortex-M

Encryption successful

29

Use in embedded C++

Minimal STL

Encryption successful

30

Use in embedded Java

Run on Java ME

Encryption successful

31

Use in embedded .NET

Run on nanoFramework

Encryption successful

32

Use in embedded Lua

Run on NodeMCU

Encryption successful

33

Use in embedded JS

Run on Espruino

Encryption successful

34

Use in embedded Python

Run on Pyboard

Encryption successful

35

Use with I2C sensor

Encrypt sensor data

Encryption successful

36

Use with SPI flash

Encrypt data before write

Encryption successful

37

Use with UART

Encrypt serial data

Encryption successful

38

Use with BLE

Encrypt Bluetooth packets

Encryption successful

39

Use with LoRa

Encrypt long-range data

Encryption successful

40

Use with Zigbee

Encrypt mesh network data

Encryption successful

41

Use with CAN bus

Encrypt automotive data

Encryption successful

42

Use with SD card

Encrypt file before write

Encryption successful

43

Use with EEPROM

Encrypt config data

Encryption successful

44

Use with RTC

Encrypt timestamped logs

Encryption successful

45

Use with GPS

Encrypt location data

Encryption successful

46

Use with camera module

Encrypt image stream

Encryption successful

47

Use with temperature sensor

Encrypt readings

Encryption successful

48

Use with motion sensor

Encrypt accelerometer data

Encryption successful

49

Use with battery monitor

Encrypt voltage logs

Encryption successful

50

Use with solar-powered device

Low energy budget

Encryption successful

Legacy Compatibility - Testcases

#

Test Case

Description

Expected Result

1

Run on Windows XP

Use Blowfish in legacy app

Encryption successful

2

Run on Windows 98

Use Blowfish DLL

Encryption successful

3

Run on MS-DOS

Use Blowfish in DOS app

Encryption successful

4

Run on Solaris

Use Blowfish in legacy Unix

Encryption successful

5

Run on AIX

Use Blowfish in IBM system

Encryption successful

6

Run on HP-UX

Use Blowfish in HP server

Encryption successful

7

Run on legacy Linux kernel

Kernel < 2.6

Encryption successful

8

Run on Palm OS

Use Blowfish in PDA app

Encryption successful

9

Run on Symbian OS

Use Blowfish in mobile app

Encryption successful

10

Run on Windows CE

Use Blowfish in embedded app

Encryption successful

11

Use in legacy VPN

Use Blowfish in OpenVPN

Tunnel established

12

Use in legacy SSH

Use Blowfish cipher in SSHv1

Connection secured

13

Use in legacy PGP

Use Blowfish in PGP 6.5

Encryption successful

14

Use in legacy GnuPG

Use Blowfish in GPG 1.x

Encryption successful

15

Use in legacy SSL

Use Blowfish in SSLv3

Cipher suite supported

16

Use in legacy TLS

Use Blowfish in TLS 1.0

Cipher suite supported

17

Use in legacy database

Encrypt fields in old DBMS

Encryption successful

18

Use in legacy ERP

Use Blowfish in SAP R/3

Encryption successful

19

Use in legacy CRM

Use Blowfish in Siebel

Encryption successful

20

Use in legacy SCADA

Use Blowfish in industrial control

Encryption successful

21

Use in legacy POS

Encrypt transactions

Encryption successful

22

Use in legacy ATM

Encrypt PIN blocks

Encryption successful

23

Use in legacy router firmware

Use Blowfish in config

Encryption successful

24

Use in legacy firewall

Use Blowfish in ruleset

Encryption successful

25

Use in legacy smart card

Use Blowfish in chip

Encryption successful

26

Use in legacy BIOS

Encrypt config data

Encryption successful

27

Use in legacy bootloader

Encrypt boot config

Encryption successful

28

Use in legacy email client

Use Blowfish in Eudora

Encryption successful

29

Use in legacy browser plugin

Use Blowfish in Netscape plugin

Encryption successful

30

Use in legacy file system

Encrypt files in FAT32

Encryption successful

31

Use in legacy backup tool

Encrypt archives

Encryption successful

32

Use in legacy compression tool

Encrypt ZIP with Blowfish

Encryption successful

33

Use in legacy scripting

Use Blowfish in VBScript

Encryption successful

34

Use in legacy Java applet

Use Blowfish in signed applet

Encryption successful

35

Use in legacy .NET 1.1

Use Blowfish in old CLR

Encryption successful

36

Use in legacy C++ app

Use Blowfish in MFC app

Encryption successful

37

Use in legacy Python 2.7

Use Blowfish module

Encryption successful

38

Use in legacy Perl script

Use Crypt::Blowfish

Encryption successful

39

Use in legacy PHP 4

Use mcrypt with Blowfish

Encryption successful

40

Use in legacy Ruby

Use OpenSSL::Cipher::Blowfish

Encryption successful

41

Use in legacy embedded OS

Use Blowfish in VxWorks

Encryption successful

42

Use in legacy automotive ECU

Encrypt CAN messages

Encryption successful

43

Use in legacy medical device

Encrypt patient data

Encryption successful

44

Use in legacy satellite system

Encrypt telemetry

Encryption successful

45

Use in legacy military system

Encrypt comms

Encryption successful

46

Use in legacy aerospace system

Encrypt avionics data

Encryption successful

47

Use in legacy telecom switch

Encrypt call metadata

Encryption successful

48

Use in legacy SCADA HMI

Encrypt operator commands

Encryption successful

49

Use in legacy industrial PLC

Encrypt control logic

Encryption successful

50

Use in legacy archival system

Encrypt stored documents

Encryption successful

Basis for bcrypt - Testcases

#

Test Case

Description

Expected Result

1

Hash password with bcrypt

Use bcrypt with default cost

Hash generated

2

Verify bcrypt hash

Compare password to hash

Match successful

3

Use bcrypt with cost 10

Moderate computational cost

Hash generated

4

Use bcrypt with cost 12

Higher computational cost

Hash generated

5

Use bcrypt with cost 4

Minimum allowed cost

Hash generated

6

Use bcrypt with cost 31

Maximum allowed cost

Hash generated

7

Use bcrypt with empty password

Hash empty string

Hash generated

8

Use bcrypt with long password

>72 characters

Truncated and hashed

9

Use bcrypt with Unicode password

UTF-8 input

Hash generated

10

Use bcrypt with binary password

Raw bytes input

Hash generated

11

Use bcrypt in Python

Use bcrypt module

Hash and verify successful

12

Use bcrypt in Java

Use BCrypt from jBCrypt

Hash and verify successful

13

Use bcrypt in Node.js

Use bcryptjs or bcrypt

Hash and verify successful

14

Use bcrypt in Go

Use golang.org/x/crypto/bcrypt

Hash and verify successful

15

Use bcrypt in PHP

Use password_hash()

Hash and verify successful

16

Use bcrypt in Ruby

Use bcrypt gem

Hash and verify successful

17

Use bcrypt in C#

Use BCrypt.Net-Next

Hash and verify successful

18

Use bcrypt in Rust

Use bcrypt crate

Hash and verify successful

19

Use bcrypt in C++

Use libbcrypt

Hash and verify successful

20

Use bcrypt in shell

Use htpasswd -B

Hash generated

21

Use bcrypt in Linux PAM

Configure PAM to use bcrypt

Authentication works

22

Use bcrypt in Django

Default password hasher

Hash and verify successful

23

Use bcrypt in Laravel

Default password hasher

Hash and verify successful

24

Use bcrypt in Flask

Use flask-bcrypt

Hash and verify successful

25

Use bcrypt in Spring Boot

Use BCryptPasswordEncoder

Hash and verify successful

26

Use bcrypt in ASP.NET

Use Identity framework

Hash and verify successful

27

Use bcrypt in WordPress

Use plugin with bcrypt

Hash and verify successful

28

Use bcrypt in Drupal

Enable bcrypt module

Hash and verify successful

29

Use bcrypt in Joomla

Use bcrypt plugin

Hash and verify successful

30

Use bcrypt in embedded system

Lightweight bcrypt

Hash generated

31

Use bcrypt in mobile app

Android/iOS

Hash and verify successful

32

Use bcrypt in browser

Use WebAssembly bcrypt

Hash and verify successful

33

Use bcrypt in cloud function

Serverless environment

Hash and verify successful

34

Use bcrypt in Docker

Containerized app

Hash and verify successful

35

Use bcrypt in CI/CD pipeline

Secure secrets

Hash and verify successful

36

Use bcrypt in database

Store bcrypt hashes

Secure storage

37

Use bcrypt in login system

Authenticate users

Secure login

38

Use bcrypt in API

Secure password endpoints

Hash and verify successful

39

Use bcrypt in IoT device

Secure local auth

Hash and verify successful

40

Use bcrypt in legacy system

Replace MD5/SHA1

Improved security

41

Use bcrypt with salt

Auto-generated salt

Unique hash

42

Use bcrypt with same password

Different salt

Different hashes

43

Use bcrypt with same password and salt

Manual salt

Same hash

44

Use bcrypt with password rotation

Rehash with new cost

Hash updated

45

Use bcrypt with password policy

Enforce strong passwords

Policy enforced

46

Use bcrypt with audit logging

Log hash generation

Logs recorded

47

Use bcrypt with 2FA

Combine with OTP

Secure login

48

Use bcrypt with SSO

Secure identity provider

Hash and verify successful

49

Use bcrypt with MFA

Multi-factor auth

Hash and verify successful

50

Use bcrypt in password manager

Store master password

Secure storage

  • Reference links