Add ElGamalCipher implementing ElGamal encryption and decryption

[polasisubash]

Description

Added a new class ElGamalCipher.java implementing the ElGamal encryption and decryption algorithm.

Features

• Implements ElGamal public-key encryption system
• Supports key generation using modular arithmetic
• Includes methods for encryption and decryption
• Demonstrates successful decryption of encrypted messages

Example Output

Original: 12345
Encrypted: (c1, c2 values)
Decrypted: 12345

Technical Notes

• Implemented under src/main/java/com/thealgorithms/ciphers/
• Successfully compiled and tested locally using Maven (BUILD SUCCESS)
• Compatible with Java 21
• Code adheres to the project’s structure and conventions

References

• Fixes issue: #13580
• Algorithm based on ElGamal public-key cryptography principles

Checklist

• Code compiles successfully
• Tests passed locally (BUILD SUCCESS)
• Follows project style and structure
• Added clear example output
• Confirmed correct encryption and decryption results

[polasisubash]

Hi maintainers 👋,
I’ve implemented the ElGamal encryption and decryption algorithm as described in the feature request (#6934).
The code compiles successfully, passes local tests, and follows project conventions.
Looking forward to your review. Thank you! 🙌

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.45%. Comparing base (2c4bf3c) to head (9d421bc).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/ciphers/ElGamalCipher.java	0.00%	15 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7064      +/-   ##
============================================
- Coverage     78.51%   78.45%   -0.07%     
  Complexity     6752     6752              
============================================
  Files           759      760       +1     
  Lines         22402    22417      +15     
  Branches       4400     4400              
============================================
- Hits          17589    17587       -2     
- Misses         4108     4124      +16     
- Partials        705      706       +1     

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[polasisubash]

✅ All checks have passed successfully.
The implementation follows the existing cipher structure and includes key generation, encryption, and decryption for ElGamal.
Kindly review when you get a chance. Thank you!
@DenizAltunkapan @alxkm
Kindly review this PR when possible. All checks have passed ✅

[polasisubash]

✅ All checks have passed successfully.
The implementation follows the existing cipher structure and includes key generation, encryption, and decryption for ElGamal.
Kindly review when you get a chance. Thank you!
@DenizAltunkapan @alxkm
Kindly review this PR when possible. All checks have passed ✅

[polasisubash]

✅ All checks have passed successfully.
The implementation follows the existing cipher structure and includes key generation, encryption, and decryption for ElGamal.
Kindly review when you get a chance. Thank you!
@DenizAltunkapan @alxkm

[polasisubash]

✅ All checks have passed successfully.
The implementation follows the existing cipher structure and includes key generation, encryption, and decryption for ElGamal.
Kindly review when you get a chance. Thank you!
@DenizAltunkapan @alxkm

[DenizAltunkapan]

@polasisubash Please always add a corresponding test class to your implementation

[DenizAltunkapan]

@polasisubash
The implementation captures the basic idea of ElGamal, but there are several critical cryptographic issues, such as invalid generator selection, missing key range constraints, and lack of input validation. Additionally, the stateful design and missing documentation/tests do not align with the repository’s standards, so the code needs refactoring before it can be merged.

Also don't forget the corresponding test class!

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution!