[mohammedanasnakhuda]

Summary

Fixes #15634.

This pull request updates the DES ECB implementation to support Unicode input using UTF-8 encoding.

Previously, characters above U+00FF could produce incorrect decrypted output because the implementation converted Unicode code points into variable-width bit sequences.

Changes

• Encode plaintext as UTF-8 bytes before converting it into bits.
• 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 encryption and decryption documentation.

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 missing NumPy in the local environment.

Compatibility notes

UTF-8 encoding changes ciphertext representation for some previously supported non-ASCII characters. Ciphertext produced by the previous encoding may not be compatible with this change.

The existing zero-padding scheme also does not preserve trailing null characters; that limitation is outside the scope of this fix.

[algorithms-keeper]

Closing this pull request as invalid

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