[vampywiz17]

Description

Related issue (if applicable): None — fixes a Matrix E2EE attachment encoding bug.

Encrypted Matrix image/file attachments sometimes fail to render in Matrix clients even when the attachment event is successfully delivered. A strict client reports an error such as:

invalid value in `iv` field: invalid base64 encoding:
invalid symbol 95, offset 7

The Matrix encrypted attachment format uses Base64URL for the JWK encryption key (file.key.k), but requires standard, unpadded Base64 for the initialization vector (file.iv).

The existing encrypt_attachment() implementation uses base64.urlsafe_b64encode() for the IV too. Depending on the random IV, this generates - or _ characters, which are rejected by strict Base64 decoders. This explains why the problem occurs intermittently.

This PR changes the IV encoding to:

iv_b64 = base64.b64encode(iv).rstrip(b"=").decode()

The change does not modify AES-256-CTR encryption, generated IV bytes, JWK key encoding, or the ciphertext hash.

A regression test forces an IV whose standard Base64 representation contains / rather than _, verifies that the serialized IV uses standard Base64, and checks successful AES-256-CTR decryption.

Matrix specification: https://spec.matrix.org/latest/client-server-api/#sending-encrypted-attachments

Checklist

• Documentation ticket created (if applicable): Not applicable; this restores compliance with the existing Matrix specification.
• The change is tested and works locally. (Live integration testing pending.)
• No commented-out code in this PR.
• No lint errors (use tox -e lint and optionally tox -e format). (Not yet run locally.)
• Test coverage added or updated (use tox -e qa). (Regression test added; execution pending.)

Testing

Anyone can help test as follows:

# Clone the proposed branch
git clone --branch fix/matrix-e2ee-attachment-iv-base64 \
    https://github.com/vampywiz17/apprise.git

cd apprise

# Run the focused regression test
tox -e qa -- -k encrypted_attachment_iv_standard_base64

# Check lint
tox -e lint

For integration testing, configure an E2EE-enabled Matrix room and send image attachments repeatedly.

Verify that attachments remain readable in Element and other strict Matrix clients, including when the generated IV contains + or /.

No live Matrix credentials are required for the regression test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5c5c3ac) to head (2714f41).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1788   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          246       246           
  Lines        40290     40307   +17     
  Branches      6950      6957    +7     
=========================================
+ Hits         40290     40307   +17     

Files with missing lines	Coverage Δ
apprise/plugins/matrix/e2ee.py	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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[caronc]

Thank you again for your PR! 🚀