[mohammedanasnakhuda]

Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist

• I have read [CONTRIBUTING.md](https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md).
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python [type hints](https://docs.python.org/3/library/typing.html).
• All functions have [doctests](https://docs.python.org/3/library/doctest.html) that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a [closing keyword](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue): "Fixes #ISSUE-NUMBER".

Summary

Fixes #15634.

This PR fixes Unicode text corruption in DES ECB encryption and decryption by using UTF-8 encoding.

Previously, characters above U+00FF could be corrupted during encryption and decryption because Unicode code points were converted into variable-width bit sequences.

Changes Made

• Convert input text to UTF-8 bytes before encryption.
• Decode decrypted bytes using UTF-8.
• Add eight regression tests covering ASCII, accented characters, the euro symbol, Japanese text, emoji, block boundaries, and embedded null characters.
• Update the documentation for encryption and decryption.

Testing

• 14 existing DES tests passed.
• 8 new regression tests passed.
• Ruff linting and formatting checks passed.
• git diff --check passed.

The broader cipher test collection was blocked by a pre-existing syntax error in maths/greatest_common_divisor.py and a missing NumPy dependency in the local environment.

Compatibility Notes

The UTF-8 change may affect compatibility with ciphertext previously generated from non-ASCII text.

The existing zero-padding scheme does not preserve trailing null characters. This is outside the scope of the current fix.