Avoid rooting cryptography through ZipArchive on browser

[Copilot]

Fixes #130650
which is regression from #122093

Using ZipArchive on browser-wasm unnecessarily retained System.Security.Cryptography, increasing trimmed application size even though WinZip AES is unsupported there.

Changes

• Exclude WinZip AES implementation files and the cryptography project reference from browser builds.
• Provide browser-specific WinZip AES stubs that continue throwing PlatformNotSupportedException.
• Keep ZipCrypto supported by removing its cryptography dependency:
  • Generate header randomness with Guid.NewGuid().
  • Clear pooled password buffers with Array.Clear.
• Add coverage ensuring browser ZipCrypto remains functional and the wasm dependency closure excludes System.Security.Cryptography.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

Suppressed comments (2)

src/libraries/System.IO.Compression/tests/ZipArchive/zip_ReadTests.cs:1072

• This browser-only test validates ZipCrypto decryption, but this PR also changes browser behavior by swapping in WinZip AES stubs. Consider also asserting that opening the AES-encrypted entry in the same archive throws PlatformNotSupportedException, so the new stub path is exercised on Browser and regressions are caught.

            ZipArchiveEntry entry = archive.GetEntry("hello.txt");
            Assert.NotNull(entry);
            Assert.Equal(ZipEncryptionMethod.ZipCrypto, entry.EncryptionMethod);

            using Stream entryStream = await OpenEntryStream(async, entry, Password);
            using StreamReader reader = new(entryStream);

src/libraries/Common/src/Interop/Windows/BCrypt/Interop.BCryptGenRandom.GetRandomBytes.cs:30

• GetCryptographicallySecureRandomBytes currently forwards to GetRandomBytes, which throws InvalidOperationException on most failures. Since the method name (and the Unix implementation) implies cryptographic RNG semantics, it should throw CryptographicException for non-OOM failures to better match RandomNumberGenerator behavior.

    // BCryptGenRandom with BCRYPT_USE_SYSTEM_PREFERRED_RNG is always cryptographically secure.
    internal static unsafe void GetCryptographicallySecureRandomBytes(byte* buffer, int length) =>
        GetRandomBytes(buffer, length);

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.Async.cs:785

• keySizeBits is computed but never used in this AES update-mode path. This is dead code and can produce warnings / confusion; it should be removed (the key size was already baked into _derivedAesKeyMaterial).

                    // Determine the actual compression method to use
                    // The AES extra field stores the real compression method
                    bool useDeflate = _compressionLevel != CompressionLevel.NoCompression;

                    Stream encryptionStream = WinZipAesStream.Create(

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Suppressed comments (2)

src/libraries/System.IO.Compression/src/System/IO/Compression/WinZipAes.PlatformNotSupported.cs:9

• The WinZipAesKeyMaterial stub is declared as internal readonly struct WinZipAesKeyMaterial; which is not valid C# syntax (types can’t be forward-declared with a trailing semicolon). This will fail to compile on browser builds.

    internal readonly struct WinZipAesKeyMaterial;

src/libraries/System.IO.Compression/src/System.IO.Compression.csproj:128

• System.Security.Cryptography doesn’t target $(NetCoreAppCurrent)-wasi (its csproj only includes windows/unix/android/apple/browser/$(NetCoreAppCurrent)), so keeping this ProjectReference for wasi will break the wasi build. The condition should exclude wasi as well as browser.

    <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography\src\System.Security.Cryptography.csproj" Condition="'$(TargetPlatformIdentifier)' != 'browser'" />

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated no new comments.

Suppressed comments (3)

src/libraries/System.IO.Compression/src/System/IO/Compression/WinZipAes.PlatformNotSupported.cs:10

• WinZipAesKeyMaterial is declared with a trailing semicolon, which isn’t valid C# (C# doesn’t support forward-declaring structs). Browser builds will fail to compile this file.

{
    internal readonly struct WinZipAesKeyMaterial;

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.Async.cs:786

• In this AES update-mode branch, int keySizeBits = GetAesKeySizeBits(Encryption); (a few lines above) is assigned but never used. If warnings are treated as errors, this will break the build; if the call is only for validation, discard the value explicitly.

                    // The AES extra field stores the real compression method
                    bool useDeflate = _compressionLevel != CompressionLevel.NoCompression;

                    Stream encryptionStream = WinZipAesStream.Create(
                        baseStream: _archive.ArchiveStream,

src/libraries/System.IO.Compression/tests/ZipArchive/zip_ReadTests.cs:1078

• This browser-only test validates ZipCrypto decryption, but it doesn’t cover creating a ZipCrypto entry on browser. Since this PR changes the ZipCrypto encryption path (header salt generation + password buffer clearing), adding a round-trip create/read assertion here would help prevent regressions.

            using MemoryStream createStream = new();
            ZipArchive createArchive = await CreateZipArchive(async, createStream, ZipArchiveMode.Create, leaveOpen: true);
            Assert.Throws<PlatformNotSupportedException>(() => createArchive.CreateEntry("aes.txt", Password, ZipEncryptionMethod.Aes256));
            await DisposeZipArchive(async, createArchive);
        }