compressed_certificate support #1909

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1. swoky commented on Nov 14, 2024

   

   swoky

   on Nov 14, 2024

   Last edited by swoky

   Author

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   i use TlsExtensionsUtils.addCompressCertificateExtension(...) ,just now i checked TlsClientProtocol , found this
   `

       case HandshakeType.certificate_status:
       case HandshakeType.certificate_url:
       case HandshakeType.client_hello:
       case HandshakeType.client_key_exchange:
       case HandshakeType.compressed_certificate:
       case HandshakeType.end_of_early_data:
       case HandshakeType.hello_request:
       case HandshakeType.hello_verify_request:
       case HandshakeType.message_hash:
       case HandshakeType.server_hello_done:
       case HandshakeType.server_key_exchange:
       case HandshakeType.supplemental_data:
       default:
           throw new TlsFatalAlert(AlertDescription.unexpected_message);
   

   `
2. winfriedgerlach

   added

   support requestCommunity assistance requestedCommunity assistance requested

   on Dec 13, 2024
3. winne42 commented on Oct 31, 2026

   

   winne42

   on Oct 31, 2026

   Contributor

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   @dghgit @peterdettman can you confirm this, then this ticket can be closed? Or should it be treated as a feature request?

   Certificate compression (RFC 8879) is not implemented in bctls. 1.78.1 only has the "preliminaries": the constants (ExtensionType.compress_certificate, HandshakeType.compressed_certificate, CertificateCompressionAlgorithm) and helpers to encode and decode the extension (TlsExtensionsUtils.addCompressCertificateExtension etc.). There is no decompression code.

   TlsClientProtocol treats an incoming CompressedCertificate message as illegal and throws TlsFatalAlert(AlertDescription.unexpected_message) (as you have already found out), so the handshake fails.

   BC doesn't send this extension by default, so your getClientExtensions must be adding it. Advertising it tells the server you can accept compressed certificates, and the server may then send one that the client can't process. When you remove it, the server has to send a normal Certificate message, which is why that works.

   The fix is what you already found: don't advertise compress_certificate(27). Compression only reduces handshake size, so you lose nothing functionally. Upgrading won't help, because the current development code doesn't implement it either.