ChaCha20

What is ChaCha20?

  • ChaCha20 is a symmetric stream cipher designed by Daniel J. Bernstein.

  • It uses the same key for encryption and decryption and is a modern, secure alternative to older ciphers like RC4 and some AES modes.

  • Known for high speed, strong security, and resistance to timing attacks—ideal for mobile and embedded platforms.

Why is ChaCha20 useful?

  • High performance – Faster than AES on many systems without AES hardware support

  • Strong security – 256-bit key, 96-bit nonce, and robust resistance to cryptographic attacks

  • Simplicity – Easy to implement with fewer chances of implementation errors

  • Constant-time operation – Prevents timing-based side-channel attacks

  • Ideal for mobile/IoT – Lightweight and efficient for resource-constrained environments

How it works

  • Key setup – Uses a 256-bit key and a 96-bit nonce

  • Keystream generation – Produces a pseudorandom keystream

  • Encryption – Plaintext is XORed with the keystream → ciphertext

  • Decryption – Ciphertext is XORed with the same keystream → original plaintext

  • Note – No padding required; suitable for variable-length data

Where is ChaCha20 used?

  • TLS/SSL (HTTPS) – In the ChaCha20-Poly1305 AEAD cipher suite

  • Mobile apps – For messaging, file encryption, and VPNs on Android/iOS

  • OpenSSH – Secure remote access using ChaCha20

  • WireGuard VPN – Lightweight VPN protocol using ChaCha20

  • Encrypted file storage – Used in tools like VeraCrypt and age

Which OSI layer does this protocol belong to?

  • Presentation Layer (Layer 6)

  • Performs encryption/decryption and ensures confidentiality and integrity

  • Formats and protects data before it’s delivered to applications

Topics in this section,

  • In this section, you are going to learn

  • Terminology

  • Version Info

ChaCha20 Version

ChaCha20 Number

Year

Core Idea / Contribution

Fundamental ChaCha20 Cipher

RFC 7539

2015

Defines ChaCha20 and Poly1305 for IETF protocols; provides a secure, fast stream cipher alternative to AES.

ChaCha20-Poly1305 in TLS

RFC 7905

2016

Specifies how to use ChaCha20-Poly1305 AEAD cipher suites in TLS and DTLS for secure communication.

Extended Nonce Variant (XChaCha20)

RFC 8439

2018

Introduces XChaCha20 with a 192-bit nonce for better nonce reuse resistance and improved security.

AEAD Construction (ChaCha20-Poly1305)

Part of RFC 7539

2015

Combines ChaCha20 with Poly1305 MAC to provide authenticated encryption (AEAD).

  • Setup

  • Setup

ChaCha20 Encryption Packet

S.No

Protocol Packets

Description

Size(Bytes)

1

ChaCha20 Encryption Packet

Used to encrypt a message using a symmetric key and nonce.

~128200+ Bytes

Symmetric Key

A 256-bit (32-byte) secret key used for encryption and decryption.

32

Nonce

A 96-bit (12-byte) unique number used once per encryption session.

12

Counter

A 32-bit (4-byte) block counter to ensure unique keystream blocks.

4

Keystream Block

Pseudorandom output generated per 64-byte block.

64 (per block)

Ciphertext

Encrypted message (plaintext XORed with keystream).

Variable

ChaCha20-Poly1305 AEAD Packet

S.No

Protocol Packets

Description

Size(Bytes)

2

ChaCha20-Poly1305 AEAD Packet

Used for authenticated encryption (AEAD) combining ChaCha20 and Poly1305

~160250+ Bytes

Symmetric Key

Same 256-bit key used for both encryption and authentication.

32

Nonce

96-bit nonce used to initialize the cipher.

12

AAD (Additional Authenticated Data)

Optional data authenticated but not encrypted.

Variable

Ciphertext

Encrypted message.

Variable

Authentication Tag

128-bit (16-byte) tag generated by Poly1305 to ensure integrity.

16

S.no

Use Case

Description

1

TLS/SSL Encryption

Used in HTTPS connections as part of the ChaCha20-Poly1305 cipher suite for secure web communication, especially on mobile devices.

2

VPN Protocols

Adopted in modern VPNs like WireGuard for fast, secure, and lightweight encryption.

3

Secure Messaging

Used in apps like Signal and WhatsApp for encrypting messages and calls.

4

Mobile & Embedded Devices

Preferred over AES on devices without hardware acceleration due to its speed and resistance to timing attacks.

5

OpenSSH

Used as an alternative to AES for encrypting SSH sessions, improving performance on low-power systems.

6

Disk & File Encryption

Employed in tools like VeraCrypt and age for encrypting files and volumes.

7

IoT Devices

Ideal for constrained environments due to its low memory and CPU requirements.

8

Browser Security

Supported by major browsers (e.g., Chrome, Firefox) for secure HTTPS connections.

9

Cryptographic Libraries

Integrated into libraries like libsodium and BoringSSL for general-purpose encryption.

10

Authenticated Encryption (AEAD)

Used with Poly1305 to provide both confidentiality and integrity in a single operation.

S.no

Feature

Description

1

Symmetric Stream Cipher

Uses the same key for encryption and decryption; operates as a stream cipher.

2

256-bit Key

Provides strong security using a 256-bit secret key.

3

96-bit Nonce

Ensures uniqueness for each encryption session to prevent keystream reuse.

4

20 Rounds of Mixing

Performs 20 rounds of cryptographic mixing for high diffusion and security.

5

No Padding Required

Stream cipher design eliminates the need for padding, simplifying implementation.

6

Constant-Time Execution

Resistant to timing attacks due to uniform execution time.

7

High Performance in Software

Faster than AES on platforms without hardware acceleration.

8

Simple and Compact Design

Easy to implement correctly, reducing risk of bugs and vulnerabilities.

9

AEAD Support (with Poly1305)

Supports authenticated encryption for confidentiality and integrity.

10

Cross-Platform Compatibility

Works efficiently on desktops, mobile devices, and embedded systems.

Symmetric Stream Cipher - Testcases

#

Test Case

Description

Expected Result

1

Valid Encryption-Decryption

Encrypt and decrypt with same key and nonce

Original plaintext recovered

2

Invalid Key

Use incorrect key for decryption

Decryption fails or returns garbage

3

Invalid Nonce

Use incorrect nonce

Decryption fails

4

Empty Plaintext

Encrypt empty string

Returns empty ciphertext

5

Empty Key

Use empty key

Error raised

6

Empty Nonce

Use empty nonce

Error raised

7

Maximum Key Length

Use 256-bit key

Encryption successful

8

Minimum Key Length

Use less than 256-bit key

Error or warning

9

Nonce Reuse

Reuse nonce with same key

Security warning

10

Unique Nonce per Message

Use new nonce for each message

Encryption secure

11

Encrypt Binary Data

Encrypt binary file

Decryption restores original

12

Encrypt Text Data

Encrypt string

Decryption returns original

13

Encrypt Unicode Text

Encrypt Unicode string

Decryption successful

14

Encrypt Large File

Encrypt 1GB file

Decryption successful

15

Encrypt Small File

Encrypt 1-byte file

Decryption successful

16

Encrypt with All-Zero Key

Use all-zero key

Encryption works but insecure

17

Encrypt with All-One Key

Use all-one key

Encryption works

18

Encrypt with Random Key

Use random 256-bit key

Encryption successful

19

Encrypt with Random Nonce

Use random 96-bit nonce

Encryption successful

20

Encrypt with Reused Key

Use same key across sessions

Works but not recommended

21

Encrypt with Reused Nonce

Reuse nonce with same key

Vulnerable to attack

22

Encrypt with Different Nonce

Use different nonce

Different ciphertext

23

Encrypt with Different Key

Use different key

Different ciphertext

24

Encrypt with Offset

Start encryption at offset

Output matches expected

25

Decrypt with Offset

Start decryption at offset

Output matches expected

26

Encrypt with Seek

Seek to position in stream

Output matches expected

27

Encrypt with Stream API

Use stream interface

Works as expected

28

Encrypt with Block API

Use block interface

Works as expected

29

Encrypt with Python

Use PyCryptodome

Encryption successful

30

Encrypt with Go

Use Go crypto library

Encryption successful

31

Encrypt with Rust

Use RustCrypto

Encryption successful

32

Encrypt with Java

Use BouncyCastle

Encryption successful

33

Encrypt with C++

Use libsodium

Encryption successful

34

Encrypt with Node.js

Use crypto module

Encryption successful

35

Encrypt with OpenSSL

Use ChaCha20-Poly1305

Encryption successful

36

Encrypt with Wrong Stream Position

Use incorrect counter

Decryption fails

37

Encrypt with Correct Stream Position

Use correct counter

Decryption successful

38

Encrypt with Short Nonce

Use 64-bit nonce

Error or warning

39

Encrypt with Long Nonce

Use 128-bit nonce

Error or warning

40

Encrypt with 96-bit Nonce

Use standard nonce size

Encryption successful

41

Encrypt with IV Misuse

Use IV as nonce

Security warning

42

Encrypt with Key Derivation

Derive key from password

Key used successfully

43

Encrypt with Key Rotation

Rotate key periodically

Encryption remains valid

44

Encrypt with Key Expiry

Use expired key

Operation denied

45

Encrypt with Key Tampering

Modify key mid-stream

Decryption fails

46

Encrypt with Logging Enabled

Log encryption steps

Logs show key/nonce usage

47

Encrypt with Debug Mode

Enable debug

Internal state visible

48

Encrypt with Performance Benchmark

Measure speed

High throughput

49

Encrypt with Side-Channel Protection

Use constant-time ops

No leakage

50

Encrypt with Compliance Check

Validate against RFC 8439

Fully compliant

256-bit Key - Testcases

#

Test Case

Description

Expected Result

1

Valid 256-bit Key

Use a 32-byte key

Encryption successful

2

Invalid Key Length (Too Short)

Use 16-byte key

Error raised

3

Invalid Key Length (Too Long)

Use 40-byte key

Error raised

4

All-Zero Key

Use 32 bytes of 0x00

Encryption works (but insecure)

5

All-One Key

Use 32 bytes of 0xFF

Encryption works

6

Random Key

Use securely generated key

Encryption successful

7

Reused Key

Use same key across sessions

Works but not recommended

8

Key Rotation

Change key periodically

Encryption remains valid

9

Key Expiry

Use expired key

Operation denied

10

Key Tampering

Modify key mid-stream

Decryption fails

11

Key Format: Hex

Provide key in hex

Accepted

12

Key Format: Binary

Provide key in binary

Accepted

13

Key Format: Base64

Provide key in base64

Decoded and accepted

14

Key Format: ASCII

Provide ASCII string

Converted or rejected

15

Key Entropy Check

Use low-entropy key

Warning issued

16

Key Entropy Check (High)

Use high-entropy key

Accepted

17

Key Derivation

Derive key from password

Key generated correctly

18

Key Agreement

Use Diffie-Hellman to derive key

Shared key used

19

Key Storage

Store key securely

Key not exposed

20

Key Retrieval

Retrieve key from vault

Key loaded correctly

21

Key Logging

Ensure key not logged

Logs clean

22

Key Audit Trail

Track key usage

Audit complete

23

Key Access Control

Restrict key access

Unauthorized blocked

24

Key Sharing

Share key securely

Key encrypted in transit

25

Key Injection

Inject key into secure module

Key accepted

26

Key Export

Export key securely

Key encrypted

27

Key Import

Import key

Key validated

28

Key Backup

Backup key

Backup successful

29

Key Restore

Restore from backup

Key restored

30

Key Comparison

Compare two 256-bit keys

Match or mismatch detected

31

Key Collision

Use two keys with same hash

Different encryption results

32

Key Reuse Detection

Detect reused key

Warning issued

33

Key Validation

Validate key length and format

Key accepted or rejected

34

Key with Nonce

Use key with valid nonce

Encryption successful

35

Key with Invalid Nonce

Use key with wrong nonce

Decryption fails

36

Key with Offset

Use key with stream offset

Output matches expected

37

Key with Seek

Seek to position in stream

Output matches expected

38

Key with Stream API

Use key in stream mode

Works as expected

39

Key with Block API

Use key in block mode

Works as expected

40

Key with AEAD

Use key with ChaCha20-Poly1305

Authenticated encryption successful

41

Key with AEAD Failure

Use wrong key for AEAD

Authentication fails

42

Key with Performance Test

Benchmark encryption

High throughput

43

Key with Side-Channel Protection

Use constant-time ops

No leakage

44

Key with Compliance Check

Validate against RFC 8439

Fully compliant

45

Key with Hardware Acceleration

Use hardware crypto

Faster encryption

46

Key with Software Library

Use PyCryptodome or libsodium

Key accepted

47

Key with Cross-Platform Use

Encrypt on one OS, decrypt on another

Decryption successful

48

Key with Language Interop

Encrypt in Python, decrypt in Go

Decryption successful

49

Key with Legacy System

Use in older system

May not be supported

50

Key with Modern System

Use in modern crypto suite

Fully supported

96-bit Nonce - Testcases

#

Test Case

Description

Expected Result

1

Valid 96-bit Nonce

Use 12-byte nonce

Encryption successful

2

Invalid Nonce Length (Too Short)

Use 8-byte nonce

Error raised

3

Invalid Nonce Length (Too Long)

Use 16-byte nonce

Error raised

4

All-Zero Nonce

Use 12 bytes of 0x00

Encryption works (not recommended)

5

All-One Nonce

Use 12 bytes of 0xFF

Encryption works

6

Random Nonce

Use securely generated nonce

Encryption successful

7

Reused Nonce with Same Key

Encrypt two messages

Security risk (keystream reuse)

8

Unique Nonce per Message

Use new nonce each time

Secure encryption

9

Nonce Collision Detection

Detect reused nonce

Warning or error

10

Nonce Logging

Log nonce used

Nonce recorded

11

Nonce Format: Hex

Provide nonce in hex

Accepted

12

Nonce Format: Binary

Provide nonce in binary

Accepted

13

Nonce Format: Base64

Provide nonce in base64

Decoded and accepted

14

Nonce Format: ASCII

Provide ASCII string

Converted or rejected

15

Nonce with Offset

Use nonce with stream offset

Output matches expected

16

Nonce with Seek

Seek to position in stream

Output matches expected

17

Nonce with Stream API

Use nonce in stream mode

Works as expected

18

Nonce with Block API

Use nonce in block mode

Works as expected

19

Nonce with AEAD

Use nonce in ChaCha20-Poly1305

Authenticated encryption successful

20

Nonce with AEAD Failure

Use wrong nonce

Authentication fails

21

Nonce with Key Rotation

Use new key with same nonce

Secure if key is unique

22

Nonce with Key Reuse

Use same key and nonce

Insecure

23

Nonce with Expired Session

Use nonce from old session

Rejected or flagged

24

Nonce with Replay Attack

Replay encrypted message

Detected if nonce tracked

25

Nonce with Logging Disabled

Disable nonce logging

No nonce in logs

26

Nonce with Debug Mode

Enable debug

Nonce visible in trace

27

Nonce with Performance Test

Benchmark with unique nonces

High throughput

28

Nonce with Side-Channel Protection

Use constant-time ops

No leakage

29

Nonce with Compliance Check

Validate against RFC 8439

Fully compliant

30

Nonce with Hardware Crypto

Use nonce in HSM

Accepted

31

Nonce with Software Library

Use PyCryptodome/libsodium

Nonce accepted

32

Nonce with Cross-Platform Use

Encrypt on one OS, decrypt on another

Decryption successful

33

Nonce with Language Interop

Encrypt in Python, decrypt in Go

Decryption successful

34

Nonce with Legacy System

Use in older system

May not support 96-bit

35

Nonce with Modern System

Use in modern crypto suite

Fully supported

36

Nonce with All-Zero Key

Use zero key and nonce

Works but insecure

37

Nonce with All-One Key

Use all-one key and nonce

Works

38

Nonce with Random Key

Use random key and nonce

Secure encryption

39

Nonce with Key Derivation

Derive key, use nonce

Works securely

40

Nonce with Key Agreement

Use DH key, apply nonce

Secure session

41

Nonce with Key Expiry

Use expired key and nonce

Operation denied

42

Nonce with Key Tampering

Modify key, use nonce

Decryption fails

43

Nonce with AEAD Replay

Replay AEAD message

Authentication fails

44

Nonce with AEAD Logging

Log nonce and tag

Traceable

45

Nonce with AEAD Integrity

Modify ciphertext

Tag verification fails

46

Nonce with AEAD Confidentiality

Modify nonce

Decryption fails

47

Nonce with AEAD Compliance

Validate nonce use

RFC 8439 compliant

48

Nonce with AEAD Performance

Benchmark AEAD with nonce

High throughput

49

Nonce with AEAD in TLS

Use in TLS 1.3

Secure session

50

Nonce with AEAD in SSH

Use in OpenSSH

Secure and supported

20 Rounds of Mixing - Testcases

#

Test Case

Description

Expected Result

1

Standard 20 Rounds

Run ChaCha20 with default rounds

Encryption successful

2

Reduced Rounds (8)

Use 8 rounds

Weaker encryption

3

Reduced Rounds (12)

Use 12 rounds

Moderate security

4

Increased Rounds (24)

Use 24 rounds

Higher security, slower

5

Round Count Validation

Set rounds to 20

Accepted

6

Invalid Round Count (0)

Set rounds to 0

Error raised

7

Invalid Round Count (Odd)

Set rounds to 15

Error or warning

8

Round Function Output

Inspect output after 20 rounds

High diffusion

9

Avalanche Effect

Flip 1 input bit

>50% output bits change

10

Round-by-Round Logging

Log state after each round

All 20 rounds logged

11

Round Key Mixing

Verify key mixing in each round

Keys influence output

12

Quarter Round Function

Test quarter round logic

Output matches spec

13

Column Round Execution

Execute column rounds

State updated correctly

14

Diagonal Round Execution

Execute diagonal rounds

State updated correctly

15

Round Symmetry

Reverse round order

Output differs

16

Round Repetition

Repeat a round

Output deviates

17

Round Skipping

Skip a round

Output deviates

18

Round Order Change

Change round sequence

Output incorrect

19

Round Function Isolation

Test one round only

Output partially diffused

20

Round Function Timing

Measure time per round

Consistent timing

21

Round Function Bit Sensitivity

Flip 1 key bit

Output changes significantly

22

Round Function Input Size

Use 512-bit input

Accepted

23

Round Function Output Size

Output is 512 bits

Validated

24

Round Function with Padding

Input with padding

Padding handled

25

Round Function with No Padding

Input aligned

No padding needed

26

Round Function with ECB Mode

Use ECB

Rounds executed

27

Round Function with CBC Mode

Use CBC

Rounds executed

28

Round Function with CFB Mode

Use CFB

Rounds executed

29

Round Function with OFB Mode

Use OFB

Rounds executed

30

Round Function with CTR Mode

Use CTR

Rounds executed

31

Round Function with IV

Use IV

IV applied before rounds

32

Round Function with Fault Tolerance

Simulate fault

Error detected

33

Round Function with Logging Disabled

Disable logs

No round logs

34

Round Function with Debug Mode

Enable debug

Round internals visible

35

Round Function with Hardware Acceleration

Use hardware

Faster execution

36

Round Function with Software Library

Use libsodium

Rounds executed correctly

37

Round Function with Compliance Check

Validate against RFC 8439

All steps compliant

38

Round Function with Side-Channel Protection

Use constant-time ops

No leakage

39

Round Function with Performance Benchmark

Measure speed

High throughput

40

Round Function with Cross-Platform Use

Encrypt on one OS, decrypt on another

Decryption successful

41

Round Function with Language Interop

Encrypt in Python, decrypt in Go

Decryption successful

42

Round Function with Legacy System

Use in older system

May not support full rounds

43

Round Function with Modern System

Use in modern crypto suite

Fully supported

44

Round Function with All-Zero Key

Use zero key

Still diffuses input

45

Round Function with All-One Key

Use all-one key

Still diffuses input

46

Round Function with Random Key

Use random key

Output unpredictable

47

Round Function with Random Nonce

Use random nonce

Output unpredictable

48

Round Function with Reused Nonce

Use same nonce

Output reused (insecure)

49

Round Function with AEAD

Use with Poly1305

Rounds executed before MAC

50

Round Function with AEAD Failure

Modify ciphertext

Authentication fails

No Padding Required - Testcases

#

Test Case

Description

Expected Result

1

Encrypt 1 Byte

Encrypt single byte

No padding added

2

Encrypt 7 Bytes

Encrypt 7-byte input

No padding added

3

Encrypt 8 Bytes

Encrypt 8-byte input

No padding added

4

Encrypt 15 Bytes

Encrypt 15-byte input

No padding added

5

Encrypt 16 Bytes

Encrypt 16-byte input

No padding added

6

Encrypt 31 Bytes

Encrypt 31-byte input

No padding added

7

Encrypt 32 Bytes

Encrypt 32-byte input

No padding added

8

Encrypt 33 Bytes

Encrypt 33-byte input

No padding added

9

Encrypt 100 Bytes

Encrypt 100-byte input

No padding added

10

Encrypt 1MB File

Encrypt large file

No padding added

11

Encrypt Empty Input

Encrypt empty string

No padding added

12

Encrypt with Stream API

Use stream interface

No padding added

13

Encrypt with Block API

Use block interface

No padding added

14

Encrypt with AEAD

Use ChaCha20-Poly1305

No padding added

15

Encrypt with Offset

Start at offset

No padding added

16

Encrypt with Seek

Seek to stream position

No padding added

17

Encrypt with Random Length

Encrypt random-length input

No padding added

18

Encrypt with Unicode

Encrypt Unicode string

No padding added

19

Encrypt with Binary Data

Encrypt binary file

No padding added

20

Encrypt with JSON

Encrypt JSON string

No padding added

21

Encrypt with XML

Encrypt XML string

No padding added

22

Encrypt with CSV

Encrypt CSV data

No padding added

23

Encrypt with Image File

Encrypt PNG/JPG

No padding added

24

Encrypt with Audio File

Encrypt MP3/WAV

No padding added

25

Encrypt with Video File

Encrypt MP4

No padding added

26

Encrypt with Log File

Encrypt .log file

No padding added

27

Encrypt with Config File

Encrypt .ini/.yaml

No padding added

28

Encrypt with Executable

Encrypt .exe/.bin

No padding added

29

Encrypt with Script File

Encrypt .py/.sh

No padding added

30

Encrypt with HTML

Encrypt HTML content

No padding added

31

Encrypt with PDF

Encrypt PDF file

No padding added

32

Encrypt with Office Document

Encrypt .docx/.xlsx

No padding added

33

Encrypt with Email Body

Encrypt email text

No padding added

34

Encrypt with Chat Message

Encrypt short message

No padding added

35

Encrypt with IoT Sensor Data

Encrypt small packets

No padding added

36

Encrypt with API Payload

Encrypt HTTP payload

No padding added

37

Encrypt with Database Field

Encrypt DB column

No padding added

38

Encrypt with Password

Encrypt password string

No padding added

39

Encrypt with Token

Encrypt access token

No padding added

40

Encrypt with Session ID

Encrypt session string

No padding added

41

Encrypt with Key Material

Encrypt key blob

No padding added

42

Encrypt with Metadata

Encrypt file metadata

No padding added

43

Encrypt with Checksum

Encrypt hash/checksum

No padding added

44

Encrypt with Timestamp

Encrypt time value

No padding added

45

Encrypt with UUID

Encrypt unique ID

No padding added

46

Encrypt with Random Bytes

Encrypt random buffer

No padding added

47

Encrypt with Structured Data

Encrypt protobuf/CBOR

No padding added

48

Encrypt with Compressed Data

Encrypt zipped file

No padding added

49

Encrypt with Encrypted Data

Re-encrypt ciphertext

No padding added

50

Encrypt with Mixed Content

Encrypt text + binary

No padding added

Constant-time Execution - Testcases

#

Test Case

Description

Expected Result

1

Encrypt Same Input Twice

Encrypt same data twice

Execution time consistent

2

Encrypt Different Inputs

Encrypt different data

Execution time consistent

3

Encrypt with All-Zero Key

Use 0x00 key

Execution time consistent

4

Encrypt with All-One Key

Use 0xFF key

Execution time consistent

5

Encrypt with Random Key

Use random key

Execution time consistent

6

Encrypt with Short Input

Encrypt 1 byte

Execution time consistent

7

Encrypt with Long Input

Encrypt 1 MB

Time scales linearly, no spikes

8

Encrypt with Similar Inputs

Encrypt similar plaintexts

No timing variation

9

Encrypt with Dissimilar Inputs

Encrypt very different data

No timing variation

10

Encrypt with Reused Nonce

Use same nonce

Execution time consistent

11

Encrypt with Unique Nonce

Use different nonce

Execution time consistent

12

Encrypt with Same Key, Different Nonce

Change nonce only

No timing difference

13

Encrypt with Same Nonce, Different Key

Change key only

No timing difference

14

Decrypt Same Ciphertext

Decrypt same data

Time consistent

15

Decrypt Different Ciphertexts

Decrypt different data

Time consistent

16

Measure Execution Time (1KB)

Encrypt 1KB

Time within expected range

17

Measure Execution Time (10KB)

Encrypt 10KB

Time scales linearly

18

Measure Execution Time (100KB)

Encrypt 100KB

Time scales linearly

19

Measure Execution Time (1MB)

Encrypt 1MB

Time scales linearly

20

Timing with Hardware Acceleration

Use hardware crypto

Constant-time maintained

21

Timing with Software Library

Use libsodium

Constant-time maintained

22

Timing with Python

Use PyCryptodome

Constant-time behavior

23

Timing with Go

Use Go crypto

Constant-time behavior

24

Timing with Rust

Use RustCrypto

Constant-time behavior

25

Timing with Java

Use BouncyCastle

Constant-time behavior

26

Timing with C++

Use Crypto++

Constant-time behavior

27

Timing with Node.js

Use crypto module

Constant-time behavior

28

Timing with .NET

Use System.Security

Constant-time behavior

29

Timing with OpenSSL

Use ChaCha20

Constant-time behavior

30

Timing with AEAD

Use ChaCha20-Poly1305

Constant-time maintained

31

Timing with AEAD Failure

Modify tag

Time does not reveal failure

32

Timing with AEAD Success

Valid tag

Time indistinguishable from failure

33

Timing with Invalid Key

Use wrong key

Time consistent

34

Timing with Invalid Nonce

Use wrong nonce

Time consistent

35

Timing with Invalid Ciphertext

Corrupt ciphertext

Time consistent

36

Timing with Invalid Length

Use incorrect length

Time consistent

37

Timing with Bit Flips

Flip 1 bit in input

No timing change

38

Timing with All-Zero Input

Encrypt 0x00 data

Time consistent

39

Timing with All-One Input

Encrypt 0xFF data

Time consistent

40

Timing with Mixed Input

Encrypt random data

Time consistent

41

Timing with Repeated Patterns

Encrypt repeating bytes

Time consistent

42

Timing with Structured Data

Encrypt JSON/XML

Time consistent

43

Timing with Binary Files

Encrypt image/audio

Time consistent

44

Timing with Short Sessions

Encrypt short message

Time consistent

45

Timing with Long Sessions

Encrypt long stream

Time scales linearly

46

Timing with Seek

Seek to stream position

Time consistent

47

Timing with Offset

Start at offset

Time consistent

48

Timing with Logging Enabled

Log during encryption

No timing leak

49

Timing with Debug Mode

Enable debug

No timing leak

50

Timing with Side-Channel Test

Simulate timing attack

No key leakage detected

High Performance in Software - Testcases

#

Test Case

Description

Expected Result

1

Encrypt 1KB with ChaCha20

Measure time

Fast encryption

2

Encrypt 1KB with AES (no hardware)

Measure time

Slower than ChaCha20

3

Encrypt 10MB with ChaCha20

Benchmark

High throughput

4

Encrypt 10MB with AES (software)

Benchmark

Lower throughput

5

Decrypt 1KB with ChaCha20

Measure time

Fast decryption

6

Decrypt 1KB with AES (software)

Measure time

Slower decryption

7

CPU Usage (ChaCha20)

Monitor CPU during encryption

Lower usage

8

CPU Usage (AES)

Monitor CPU during encryption

Higher usage

9

Memory Usage (ChaCha20)

Monitor memory

Efficient usage

10

Memory Usage (AES)

Monitor memory

Slightly higher

11

Mobile Device Performance

Encrypt on Android

ChaCha20 faster

12

Embedded Device Performance

Encrypt on IoT board

ChaCha20 faster

13

Desktop Performance

Encrypt on x86 CPU

ChaCha20 performs well

14

Server Performance

Encrypt on server without AES-NI

ChaCha20 outperforms AES

15

Encrypt with Python

Use PyCryptodome

ChaCha20 faster

16

Encrypt with Go

Use Go crypto

ChaCha20 faster

17

Encrypt with Rust

Use RustCrypto

ChaCha20 faster

18

Encrypt with Java

Use BouncyCastle

ChaCha20 faster

19

Encrypt with Node.js

Use crypto module

ChaCha20 faster

20

Encrypt with C++

Use libsodium

ChaCha20 faster

21

Encrypt with .NET

Use System.Security

ChaCha20 performs well

22

Encrypt with OpenSSL

Use ChaCha20

High performance

23

Encrypt with WebAssembly

Run in browser

ChaCha20 performs well

24

Encrypt with ARM CPU

Use Raspberry Pi

ChaCha20 faster

25

Encrypt with RISC-V

Use RISC-V board

ChaCha20 performs well

26

Encrypt with No SIMD

Disable vector instructions

ChaCha20 still fast

27

Encrypt with SIMD

Use vectorized ChaCha20

Even faster

28

Encrypt with Multi-threading

Parallel encryption

High throughput

29

Encrypt with Single Thread

No parallelism

Still fast

30

Encrypt with Low Power Mode

Use energy-saving CPU mode

ChaCha20 efficient

31

Encrypt with Battery Constraints

Mobile device test

ChaCha20 conserves power

32

Encrypt with AES-NI Disabled

Disable AES hardware

ChaCha20 faster

33

Encrypt with AES-NI Enabled

Enable AES hardware

AES faster

34

Encrypt with AES-GCM

Compare with ChaCha20-Poly1305

ChaCha20 faster in software

35

Encrypt with ChaCha20-Poly1305

Use AEAD mode

High performance

36

Encrypt with Short Messages

Encrypt 64-byte packets

ChaCha20 faster

37

Encrypt with Long Messages

Encrypt 1MB file

ChaCha20 scales well

38

Encrypt with Streaming Data

Encrypt live stream

ChaCha20 performs well

39

Encrypt with File System

Encrypt files on disk

ChaCha20 faster

40

Encrypt with Network Packets

Encrypt UDP/TCP payloads

ChaCha20 faster

41

Encrypt with TLS

Use ChaCha20 in TLS 1.3

Fast handshake and data

42

Encrypt with SSH

Use ChaCha20 in OpenSSH

Fast session setup

43

Encrypt with VPN

Use ChaCha20 in WireGuard

High throughput

44

Encrypt with Messaging App

Use ChaCha20 in Signal

Fast message encryption

45

Encrypt with Email Client

Use ChaCha20 in S/MIME

Fast encryption

46

Encrypt with Cloud Function

Run in serverless environment

ChaCha20 efficient

47

Encrypt with Container

Run in Docker

ChaCha20 performs well

48

Encrypt with Virtual Machine

Run in VM

ChaCha20 performs well

49

Encrypt with No Hardware Support

Use generic CPU

ChaCha20 outperforms AES

50

Encrypt with Hardware Support

Use AES-NI

AES faster, but ChaCha20 still competitive

Design - Testcases

#

Test Case

Description

Expected Result

1

Minimal Implementation

Implement core ChaCha20 in <200 lines

Functional and secure

2

No Lookup Tables

Verify no S-boxes or tables used

Confirmed

3

No Branching on Secret Data

Check for constant-time logic

No timing leaks

4

Stateless Core Function

Test core function

Stateless and deterministic

5

Easy Key Setup

Initialize with 256-bit key

Simple and direct

6

Easy Nonce Setup

Initialize with 96-bit nonce

Simple and direct

7

No Padding Logic

Encrypt arbitrary-length input

No padding required

8

No Mode-Specific Logic

No need for ECB/CBC logic

Simplified design

9

No IV Misuse Risk

Use nonce instead of IV

Safer design

10

No Key Expansion Needed

Use key directly

No extra derivation

11

No Complex State Machine

Encrypt with simple loop

Easy to follow

12

No External Dependencies

Implement without libraries

Works standalone

13

Easy to Port

Port to embedded C

Works with minimal changes

14

Easy to Port to Python

Implement in Python

Works with basic types

15

Easy to Port to Rust

Implement in Rust

Safe and compact

16

Easy to Port to Go

Implement in Go

Simple and readable

17

Easy to Port to JavaScript

Implement in JS

Works in browser

18

Easy to Port to Java

Implement in Java

Works with standard libs

19

Easy to Port to C++

Implement in C++

Works with STL

20

Easy to Port to .NET

Implement in C#

Works with built-in types

21

Easy to Audit

Review code manually

Logic is clear

22

Easy to Test

Write unit tests

All pass

23

Easy to Debug

Trace internal state

Predictable behavior

24

Easy to Document

Add comments

Code is self-explanatory

25

Easy to Maintain

Update implementation

Minimal effort

26

Easy to Integrate

Add to existing app

Minimal dependencies

27

Easy to Validate

Compare against test vectors

Matches expected output

28

Easy to Benchmark

Measure performance

Consistent results

29

Easy to Optimize

Improve performance

No structural changes

30

Easy to Secure

Avoid side-channel leaks

Constant-time logic

31

No Key Schedule Bugs

Use key directly

No expansion errors

32

No Block Alignment Issues

Encrypt any length

No alignment logic

33

No Cipher Mode Confusion

Stream cipher only

No mode selection needed

34

No MAC Confusion

Use Poly1305 separately

Clear separation

35

No Buffer Overflows

Use safe indexing

No crashes

36

No Memory Leaks

Use managed memory

Clean execution

37

No Undefined Behavior

Use standard types

Safe execution

38

No Platform-Specific Code

Run on any OS

Portable

39

No Architecture-Specific Code

Run on any CPU

Portable

40

No Licensing Issues

Use open-source license

Free to use

41

No Patent Restrictions

Use freely

No legal risk

42

No Obscure Constants

Use readable constants

Easy to verify

43

No Hidden State

All state is visible

Transparent logic

44

No External RNG Required

Deterministic output

No entropy needed

45

No Complex Error Handling

Simple return values

Easy to manage

46

No Special Hardware Needed

Run on basic CPU

No acceleration required

47

No Special Compiler Flags

Compile with defaults

Works out of the box

48

No Special Libraries Needed

Use standard language features

Lightweight

49

No Complex Build System

Compile with single file

Easy to build

50

No Special Permissions

Run in user space

No elevated access needed

AEAD Support (with poly1305) - Testcases

#

Test Case

Description

Expected Result

1

Valid AEAD Encryption

Encrypt with key, nonce, plaintext, AAD

Ciphertext and tag generated

2

Valid AEAD Decryption

Decrypt with correct inputs

Plaintext recovered

3

Invalid Tag

Modify authentication tag

Decryption fails

4

Modified Ciphertext

Alter ciphertext

Authentication fails

5

Modified AAD

Alter associated data

Authentication fails

6

Missing AAD

Omit AAD during decryption

Authentication fails

7

Empty AAD

Use empty AAD

Encryption and decryption succeed

8

Empty Plaintext

Encrypt empty message with AAD

Tag generated, no ciphertext

9

Empty Ciphertext

Decrypt empty ciphertext with AAD

Empty plaintext recovered

10

Empty Tag

Omit tag

Decryption fails

11

Valid AAD

Use valid associated data

Authenticated successfully

12

Long AAD

Use 1MB AAD

Authenticated successfully

13

Short AAD

Use 1-byte AAD

Authenticated successfully

14

Valid Nonce

Use 96-bit nonce

Encryption succeeds

15

Reused Nonce

Reuse nonce with same key

Security risk (test warning)

16

Unique Nonce

Use new nonce per message

Secure encryption

17

Valid Key

Use 256-bit key

Encryption succeeds

18

Invalid Key Length

Use 128-bit key

Error raised

19

Valid Tag Length

Use 16-byte tag

Authentication succeeds

20

Invalid Tag Length

Use 8-byte tag

Authentication fails

21

AEAD with JSON AAD

Use JSON as AAD

Authenticated successfully

22

AEAD with Binary AAD

Use binary AAD

Authenticated successfully

23

AEAD with Unicode AAD

Use Unicode AAD

Authenticated successfully

24

AEAD with Structured AAD

Use structured data

Authenticated successfully

25

AEAD with Random AAD

Use random bytes

Authenticated successfully

26

AEAD with Repeated AAD

Use same AAD across messages

Works if nonce is unique

27

AEAD with No AAD

Skip AAD

Still secure

28

AEAD with All-Zero Key

Use 0x00 key

Works but insecure

29

AEAD with All-One Key

Use 0xFF key

Works

30

AEAD with Random Key

Use securely generated key

Works securely

31

AEAD with All-Zero Nonce

Use 0x00 nonce

Works but insecure

32

AEAD with Random Nonce

Use securely generated nonce

Secure encryption

33

AEAD with Short Message

Encrypt 1-byte message

Works

34

AEAD with Long Message

Encrypt 1MB message

Works

35

AEAD with Streaming Data

Encrypt stream chunks

Authenticated per chunk

36

AEAD with File Data

Encrypt file contents

Authenticated successfully

37

AEAD with Network Packet

Encrypt UDP payload

Authenticated successfully

38

AEAD with TLS

Use in TLS 1.3

Secure session

39

AEAD with SSH

Use in OpenSSH

Secure session

40

AEAD with VPN

Use in WireGuard

Secure tunnel

41

AEAD with IoT Device

Encrypt sensor data

Secure and efficient

42

AEAD with Mobile App

Encrypt messages

Secure and fast

43

AEAD with Web App

Encrypt API payload

Authenticated successfully

44

AEAD with Email

Encrypt email body

Authenticated successfully

45

AEAD with Token

Encrypt and authenticate token

Secure token

46

AEAD with Session ID

Encrypt session data

Authenticated successfully

47

AEAD with Replay Attack

Replay encrypted message

Detected via nonce tracking

48

AEAD with Timing Attack

Measure decryption time

Constant-time behavior

49

AEAD with Compliance Check

Validate against RFC 8439

Fully compliant

50

AEAD with Cross-Platform Use

Encrypt in Python, decrypt in Go

Decryption successful

Cross-Platform Compatibility - Testcases

#

Test Case

Description

Expected Result

1

Encrypt on Windows

Run ChaCha20 on Windows OS

Encryption successful

2

Encrypt on Linux

Run ChaCha20 on Linux OS

Encryption successful

3

Encrypt on macOS

Run ChaCha20 on macOS

Encryption successful

4

Encrypt on Android

Run ChaCha20 in Android app

Encryption successful

5

Encrypt on iOS

Run ChaCha20 in iOS app

Encryption successful

6

Encrypt on Raspberry Pi

Run ChaCha20 on ARM CPU

Encryption successful

7

Encrypt on Arduino

Run ChaCha20 on microcontroller

Encryption successful

8

Encrypt on ESP32

Run ChaCha20 on embedded Wi-Fi chip

Encryption successful

9

Encrypt on WebAssembly

Run ChaCha20 in browser

Encryption successful

10

Encrypt on Docker

Run ChaCha20 in container

Encryption successful

11

Encrypt on Virtual Machine

Run ChaCha20 in VM

Encryption successful

12

Encrypt on Cloud Function

Run ChaCha20 in serverless environment

Encryption successful

13

Encrypt with Python

Use PyCryptodome

Works on all platforms

14

Encrypt with Go

Use Go crypto library

Works on all platforms

15

Encrypt with Rust

Use RustCrypto

Works on all platforms

16

Encrypt with Java

Use BouncyCastle

Works on all platforms

17

Encrypt with Node.js

Use crypto module

Works on all platforms

18

Encrypt with C++

Use libsodium

Works on all platforms

19

Encrypt with .NET

Use System.Security

Works on Windows, Linux, macOS

20

Encrypt with OpenSSL

Use ChaCha20 CLI

Works on all platforms

21

Encrypt with Android NDK

Use native C/C++

Works on Android

22

Encrypt with iOS Swift

Use CryptoKit

Works on iOS

23

Encrypt with Flutter

Use Dart plugin

Works on Android and iOS

24

Encrypt with React Native

Use JS module

Works on Android and iOS

25

Encrypt with Xamarin

Use C#

Works on Android and iOS

26

Encrypt with Unity

Use C# plugin

Works on all gaming platforms

27

Encrypt with Web App

Run in browser

Works on all OSes

28

Encrypt with CLI Tool

Run from terminal

Works on all OSes

29

Encrypt with API Server

Run in backend

Works on all cloud platforms

30

Encrypt with IoT Gateway

Run on edge device

Encryption successful

31

Encrypt with Smartwatch

Run on wearable OS

Encryption successful

32

Encrypt with Smart TV

Run on Android TV

Encryption successful

33

Encrypt with Automotive OS

Run on car infotainment system

Encryption successful

34

Encrypt with POS Terminal

Run on payment device

Encryption successful

35

Encrypt with ATM Software

Run on banking terminal

Encryption successful

36

Encrypt with Medical Device

Run on embedded health monitor

Encryption successful

37

Encrypt with Industrial Controller

Run on PLC

Encryption successful

38

Encrypt with Satellite Firmware

Run on space-grade hardware

Encryption successful

39

Encrypt with Drone Firmware

Run on flight controller

Encryption successful

40

Encrypt with Game Console

Run on console OS

Encryption successful

41

Encrypt with Chromebook

Run in ChromeOS

Encryption successful

42

Encrypt with eReader

Run on Kindle or Kobo

Encryption successful

43

Encrypt with Smart Speaker

Run on voice assistant

Encryption successful

44

Encrypt with Smart Home Hub

Run on home automation device

Encryption successful

45

Encrypt with Router Firmware

Run on OpenWRT

Encryption successful

46

Encrypt with NAS Device

Run on storage server

Encryption successful

47

Encrypt with Legacy System

Run on older OS

Encryption successful

48

Encrypt with ARM64

Run on 64-bit ARM CPU

Encryption successful

49

Encrypt with x86_64

Run on Intel/AMD CPU

Encryption successful

50

Encrypt with RISC-V

Run on open-source CPU

Encryption successful

  • Reference links