Feat: TLS 1.3 certificate compression by aidankeefe2022 · Pull Request #11615 · wolfSSL/wolfssl

aidankeefe2022 · 2026-09-30T22:04:59Z

Description

When enabled with --enable-cert-compression the feature in negotiated by all TLS1.3 handshakes and able to be turned off at runtime with setters. Looking for feedback on this.

Compression API

Added a compression api that acts on wc_CompressionData object it allows for state tracking of compressed data.
It is a part of two layers. The CompressionData API calls lower-level public algorithm specific APIs. This was to reduce complexity of adding more compression Algs over time to certificate_compression. It also is general purpose and allows for users to swap out compression Algs with out large code changes.

Certificate Compression

When enabled it is on by default and will negotiate all compiled in compression Algs currently it is only supporting zlib but can be extended in the future easily. Users can turn off tls_cert_compression per SSL object or CTX object and set custom algorithm lists via setters turn off is just setting empty list.

Receiving Compressed Cert

Checks if we requested a compressed cert and that the algorithm used is one we support/requested + other RFC checks.
Decompresses the cert and passed it right to the plain Certificate logic. If we are resuming we just go straight to passing out already uncompressed cert msg to Certificate logic.

Sending Compressed Cert

Checks if we requested a cert and if the cert we are getting was one the algorithms we negotiated + rest of RFC checks. We build the compressed cert message and then compress it with out negotiated algorithm. This is then saved in the SSL object and we go into our fragmenting loop.

Tests

Compression API (`wc_CompressionData_*`) — `tests/api/test_compress.c`

RoundTrip: compress → decompress restores the original data, and the compressed output is smaller.
InitWithCompressedData: known-answer zlib vector decompresses to the expected plaintext.
ToBuffer: CompToBuf / DeCompToBuf work with caller-supplied buffers.
BadArgs: NULL inputs, zero lengths, unknown algorithm IDs and use after a failed init are all rejected.

Certificate Compression (RFC 8879)

Extension unit tests (test_tls_parse.c, test_tls_msgtype.c)

Parsing picks zlib when offered (even after unsupported IDs), accepts lists with no supported algorithm, and rejects malformed lists.
Size and write passes agree, and the exact wire bytes are emitted in ClientHello and CertificateRequest.
The extension is allowed only in ClientHello and CertificateRequest.

Handshake tests (test_tls13_cert_compression.c, new)

roundTrip: server-auth and mutual-auth handshakes, with a size check showing compression was actually used.
turnoff: setting the algorithm list to NULL disables the extension at the CTX or SSL level, and it can be re-enabled.
fragment: CompressedCertificate split across records via max_fragment_length, with WANT_WRITE injected at every write.
dtls13: the same coverage over DTLS 1.3.
pha: the reply to a post-handshake CertificateRequest is compressed.
malformed: each header field is broken in turn, checking the expected error and alert (illegal_parameter / bad_certificate).
fallback: when compression fails to allocate, a plain Certificate is sent instead, and OCSP staples are kept.

tests/quic.c now treats compressed_certificate as a Certificate record.

Docs

all public docs are updated and added for new funcs

Copilot

Copilot review overview

🟡 Changes recommended

A supported build configuration fails to compile, and one protocol error path sends the wrong RFC-mandated alert.

Review effort: Balanced
Findings: 1 · 1

Open (2)

Fix undefined tmp usage when realloc is disabled · New
Return illegal_parameter for unadvertised compression algorithms · New

What changed in this PR

Adds RFC 8879 certificate compression for TLS/DTLS 1.3 using zlib.

Changes:

Adds certificate-compression negotiation, APIs, message handling, and lifecycle management.
Introduces reusable compression-data APIs and documentation.
Adds extensive TLS, DTLS, QUIC, parser, fragmentation, and fallback tests.

File	Description
`wolfssl/wolfcrypt/compress.h`	Defines compression algorithms and data APIs.
`wolfssl/ssl.h`	Exposes certificate-compression configuration APIs.
`wolfssl/internal.h`	Adds protocol constants and internal state.
`wolfcrypt/src/compress.c`	Implements compression-data operations.
`src/tls13.c`	Implements compressed certificate send/receive handling.
`src/tls.c`	Implements extension negotiation and serialization.
`src/ssl.c`	Resets compression state on reuse.
`src/internal.c`	Manages compression resources and message validation.
`src/dtls13.c`	Supports compressed certificates in DTLS 1.3.
`tests/quic.c`	Recognizes compressed certificates in QUIC tests.
`tests/api/test_tls13_cert_compression.h`	Declares certificate-compression tests.
`tests/api/test_tls13_cert_compression.c`	Tests negotiation, malformed input, fragmentation, and fallback.
`tests/api/test_tls_parse.h`	Registers extension parser tests.
`tests/api/test_tls_parse.c`	Tests extension parsing and writing.
`tests/api/test_tls_msgtype.h`	Registers message-type tests.
`tests/api/test_tls_msgtype.c`	Tests extension placement restrictions.
`tests/api/test_compress.h`	Registers compression-data tests.
`tests/api/test_compress.c`	Tests compression-data APIs.
`tests/api/include.am`	Adds new tests to Autotools.
`tests/api.c`	Registers the new test suite.
`doc/dox_comments/header_files/ssl.h`	Documents TLS configuration APIs.
`doc/dox_comments/header_files/compress.h`	Documents compression-data APIs.
`configure.ac`	Adds the Autotools feature option.
`CMakeLists.txt`	Adds the CMake feature option and tests.
`cmake/options.h.in`	Exposes the generated feature macro.

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Copilot

Copilot review overview

🟡 Changes recommended

RFC duplicate handling, user-settings prerequisites, and split read/write PHA state propagation remain incomplete.

Review effort: Balanced
Findings: 1 · 2

Open (3)

Missing TLS extensions prerequisite for certificate compression · New
Incomplete duplicate algorithm validation after early selection · New
Duplicate certificate compression algorithms are accepted · New

Resolved since last review (2)

Fix undefined tmp usage when realloc is disabled
Return illegal_parameter for unadvertised compression algorithms

wolfSSL-Fenrir-bot

Fenrir Automated Review — PR #11615

Scan targets checked: wolfcrypt-src, wolfcrypt-bugs, wolfssl-src, wolfssl-bugs
Coverage: 9 of 16 in-scope changed file(s) opened by the reviewer; not opened: src/dtls13.c, src/ssl_api_hs.c, tests/api.c, tests/api/test_compress.c, tests/quic.c, wolfssl/internal.h, wolfssl/ssl.h

Fenrir result: Approved ✅

No new issues found in the changed files.

Advisory only — this automated result does not count as a GitHub approval.

Review tier: Lite

github-actions · 2026-10-01T17:54:03Z

retest this please

github-actions · 2026-10-01T17:57:33Z

MemBrowse Memory Report

gcc-arm-cortex-m3

FLASH: .text +8 B (+0.0%, 127,953 B / 262,144 B, total: 49% used)

gcc-arm-cortex-m4-dtls13

FLASH: .text -192 B (-0.1%, 190,916 B / 1,048,576 B, total: 18% used)

gcc-arm-cortex-m4-openssl-compat

FLASH: .text -256 B (-0.0%, 788,892 B / 1,048,576 B, total: 75% used)

gcc-arm-cortex-m4-pq

FLASH: .text -256 B (-0.1%, 306,800 B / 1,048,576 B, total: 29% used)

gcc-arm-cortex-m4-rsa-only

FLASH: .text -192 B (-0.1%, 337,008 B / 1,048,576 B, total: 32% used)

gcc-arm-cortex-m4-tls13

FLASH: .text -256 B (-0.1%, 245,726 B / 262,144 B, total: 94% used)

gcc-arm-cortex-m7

FLASH: .text +64 B (+0.0%, 206,700 B / 262,144 B, total: 79% used)

gcc-arm-cortex-m7-pq

FLASH: .text -256 B (-0.1%, 307,760 B / 1,048,576 B, total: 29% used)

gcc-arm-cortex-m7-tls13

FLASH: .text -256 B (-0.1%, 245,790 B / 262,144 B, total: 94% used)
No memory changes detected for:
gcc-arm-cortex-m0plus
gcc-arm-cortex-m4
gcc-arm-cortex-m4-baremetal
gcc-arm-cortex-m4-crypto-only
gcc-arm-cortex-m4-min-ecc
gcc-arm-cortex-m4-pkcs7
gcc-arm-cortex-m4-sp-math
gcc-arm-cortex-m4-tls12
linuxkm-pie
linuxkm-standard
stm32-sim-stm32h753

Checkpoint of the compress_certificate work: - compress_certificate extension: build options, parsing, and offering it in ClientHello and in CertificateRequest. - Receiving CompressedCertificate: decompress with zlib, enforce the size limit and exact uncompressed length, send bad_certificate alerts, keep the buffer across async/non-blocking OCSP re-entry. - wc_CompressionData helpers in wolfCrypt. - Split the TLS 1.3 Certificate body writing into WriteTls13CertHeader and WriteTls13CertEntries, which write into any buffer. - Fix AddCertExt writing an empty extension one byte past the fragment when a record boundary falls inside it. - Unit tests, and OpenSSL interop script cert-compression-interop.sh. Sending compressed certificates is not implemented yet.

Cert Compression is now impl. Also changes compress cert api

Need to look at multi thread tests and all tests in general Move compressed cert cache to cert-compression-cache branch Remove the per-CTX compressed Certificate cache (isCacheReady, cachedCertMsg, compressedCertCache, usingCompressedCertCache) and its threaded test. Each connection compresses its own Certificate again. The cache work continues on the cert-compression-cache branch. fixed testing for compression Removed all compression extensions and cache Added docs to compression API skoll fixes and more testing + setters skoll review reverted accidental reformat finished codespell

padelsbach · 2026-10-02T17:41:09Z

jenkins retest this please

Copilot AI balanced review requested due to automatic review settings September 30, 2026 22:04

Copilot started reviewing on behalf of aidankeefe2022 September 30, 2026 22:05 View session

Copilot AI reviewed Sep 30, 2026

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Comment thread wolfcrypt/src/compress.c

Comment thread src/tls13.c

aidankeefe2022 force-pushed the cert-compression branch from f7ad8de to 6e7dc71 Compare October 1, 2026 15:58

aidankeefe2022 requested review from wolfSSL-Fenrir-bot and a balanced review from Copilot October 1, 2026 17:01

Copilot started reviewing on behalf of aidankeefe2022 October 1, 2026 17:01 View session

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Comment thread wolfssl/internal.h Outdated

Comment thread src/tls.c

Comment thread src/tls13.c

wolfSSL-Fenrir-bot reviewed Oct 1, 2026

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aidankeefe2022 marked this pull request as ready for review October 1, 2026 17:53

aidankeefe2022 added 3 commits October 1, 2026 11:59

Added Cert compression sending + CompCert API

696febc

Cert Compression is now impl. Also changes compress cert api

aidankeefe2022 force-pushed the cert-compression branch from ab524b2 to 4b626bc Compare October 1, 2026 17:59

aidankeefe2022 self-assigned this Oct 1, 2026

aidankeefe2022 changed the title ~~Cert compression~~ Feat: TLS 1.3 certificate compression Oct 1, 2026

fixing compiler warning

65e4a6e

aidankeefe2022 force-pushed the cert-compression branch from 1206c7e to 65e4a6e Compare October 2, 2026 16:50

aidankeefe2022 assigned wolfSSL-Bot and unassigned aidankeefe2022 Oct 2, 2026

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Feat: TLS 1.3 certificate compression - #11615

Feat: TLS 1.3 certificate compression#11615
aidankeefe2022 wants to merge 4 commits into
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aidankeefe2022 commented Sep 30, 2026 •

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aidankeefe2022 commented Sep 30, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description

Compression API

Certificate Compression

Receiving Compressed Cert

Sending Compressed Cert

Tests

Compression API (wc_CompressionData_*) — tests/api/test_compress.c

Certificate Compression (RFC 8879)

Docs

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Copilot review overview

🟡 Changes recommended

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Fenrir Automated Review — PR #11615

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aidankeefe2022 commented Sep 30, 2026 •

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Compression API (`wc_CompressionData_*`) — `tests/api/test_compress.c`

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