UTF-8 charset handling causes AES/JWE interoperability test failures #127

Bug Report Checklist

• Have you provided a code sample to reproduce the issue?
• Have you tested with the latest release to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

AES/JWE interoperability tests fail on some environments due to inconsistent charset handling during string-to-byte conversions. The implementation currently relies on the platform default charset, which can produce different byte sequences for non-ASCII characters depending on the runtime environment. As a result, encryption/decryption behavior is not deterministic across systems, causing interoperability test failures.

To Reproduce

1. Run the AES/JWE interoperability tests.
2. Use plaintext or payload containing non-ASCII characters.
3. Observe that the generated byte arrays differ from the expected output on environments with different default character encodings.

Expected behavior

String input should always be encoded using UTF-8 so that encryption and decryption produce deterministic, platform-independent results and the interoperability tests pass consistently.

Screenshots

Attached below is the failing test output demonstrating the issue.

Additional context

• Environment: Java/Maven-based project
• Issue observed during AES/JWE interoperability test execution
• The behavior is triggered when processing non-ASCII characters due to platform-dependent string-to-byte conversion

Related issues/PRs

None found at the time of reporting.

Suggest a fix/enhancement

Explicitly use StandardCharsets.UTF_8 for all string-to-byte conversions in the AES/JWE processing path and ensure related tests use the same encoding when constructing expected byte arrays.

Assignment

I'd like to work on this issue and submit a fix. Please assign it to me if it's available.