src: simplify handling of kNoAuthTagLength

[tniessen]

Since #61084, the kNoAuthTagLength constant is only used

• during the entire lifetime of non-authenticating cipher/decipher objects and
• during the initialization of authenticating cipher/decipher objects.

In particular, it is never used during the lifetime of an authenticating cipher/decipher object once that object has been initialized. (Before said change, the constant was also used for ciphers in GCM mode to indicate that the user had not specified the length of the authentication tag in advance, but the authentication tag length must now always be specified or defaults to the block size in the case of GCM mode.)

This commit simplifies the handling of kNoAuthTagLength based on the knowledge that it is not a valid value for AEAD ciphers beyond initialization.

[nodejs-github-bot]

Review requested:

• @nodejs/crypto

[codecov]

Codecov Report

❌ Patch coverage is 73.07692% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.54%. Comparing base (05d6b9b) to head (dc8669c).
⚠️ Report is 139 commits behind head on main.

Files with missing lines	Patch %	Lines
src/crypto/crypto_cipher.cc	73.07%	2 Missing and 5 partials ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #61192 +/- ##
=======================================
Coverage 88.53% 88.54% =======================================
Files 703 703 Lines 208599 208579 -20 Branches 40229 40220 -9 =======================================
- Hits 184685 184676 -9 + Misses 15939 15911 -28 - Partials 7975 7992 +17 

Files with missing lines	Coverage Δ
src/crypto/crypto_cipher.cc	77.43% <73.07%> (-1.04%)	⬇️

... and 32 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70618/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70637/

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----------------------------------- PR info ------------------------------------
Title src: simplify handling of kNoAuthTagLength (#61192)
⚠ Could not retrieve the email or name of the PR author's from user's GitHub profile!
Branch tniessen:src-simplify-knoauthtaglength -> nodejs:main
Labels crypto, c++, author ready, needs-ci
Commits 1
- src: simplify handling of kNoAuthTagLength
Committers 1
- Tobias Nießen <tniessen@tnie.de>
PR-URL: https://github.com/nodejs/node/pull/61192
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/61192
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
--------------------------------------------------------------------------------
ℹ This PR was created on Sun, 28 Dec 2025 12:25:18 GMT
✔ Approvals: 1
✔ - Colin Ihrig (@cjihrig): https://github.com/nodejs/node/pull/61192#pullrequestreview-3614804140
✘ This PR needs to wait 71 more hours to land (or 0 minutes if there is one more approval)
✔ Last GitHub CI successful
ℹ Last Full PR CI on 2025-12-30T19:17:12Z: https://ci.nodejs.org/job/node-test-pull-request/70637/
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https://github.com/nodejs/node/actions/runs/20639737695

[nodejs-github-bot]

Landed in a86db6b