From d14d6ae74514b89f548aa7886503a2facc23fc44 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tobias=20Nie=C3=9Fen?= <tobias.niessen@tuwien.ac.at>
Date: Wed, 3 Apr 2024 14:52:51 +0100
Subject: [PATCH] crypto: deprecate implicitly shortened GCM tags

This introduces a doc-only deprecation of using GCM authentication tags
that are shorter than the cipher's block size, unless the user specified
the authTagLength option.

Refs: https://github.com/nodejs/node/issues/52327
---
 doc/api/crypto.md                             |  5 +++++
 doc/api/deprecations.md                       | 19 +++++++++++++++++
 src/crypto/crypto_cipher.cc                   | 13 ++++++++++++
 .../test-crypto-gcm-decipheriv-short-tag.js   | 21 +++++++++++++++++++
 4 files changed, 58 insertions(+)
 create mode 100644 test/parallel/test-crypto-gcm-decipheriv-short-tag.js

diff --git a/doc/api/crypto.md b/doc/api/crypto.md
index 8b0ca04b486600..44a4e249759b3a 100644
--- a/doc/api/crypto.md
+++ b/doc/api/crypto.md
@@ -891,6 +891,11 @@ When passing a string as the `buffer`, please consider
 <!-- YAML
 added: v1.0.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/52345
+    description: Using GCM tag lengths other than 128 bits without specifying
+                 the `authTagLength` option when creating `decipher` is
+                 deprecated.
   - version: v15.0.0
     pr-url: https://github.com/nodejs/node/pull/35093
     description: The buffer argument can be a string or ArrayBuffer and is
diff --git a/doc/api/deprecations.md b/doc/api/deprecations.md
index 962b96acaf30de..75e3468a9c9129 100644
--- a/doc/api/deprecations.md
+++ b/doc/api/deprecations.md
@@ -3619,6 +3619,25 @@ Calling `Hmac` class directly with `Hmac()` or `new Hmac()` is
 deprecated due to being internals, not intended for public use.
 Please use the [`crypto.createHmac()`][] method to create Hmac instances.
 
+### DEP0182: Short GCM authentication tags without explicit `authTagLength`
+
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/52345
+    description: Documentation-only deprecation.
+-->
+
+Type: Documentation-only (supports [`--pending-deprecation`][])
+
+Applications that intend to use authentication tags that are shorter than the
+default authentication tag length should set the `authTagLength` option of the
+[`crypto.createDecipheriv()`][] function to the appropriate length.
+
+For ciphers in GCM mode, the [`decipher.setAuthTag()`][] function accepts
+authentication tags of any valid length (see [DEP0090](#DEP0090)). This behavior
+is deprecated to better align with recommendations per [NIST SP 800-38D][].
+
 [NIST SP 800-38D]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
 [RFC 6066]: https://tools.ietf.org/html/rfc6066#section-3
 [RFC 8247 Section 2.4]: https://www.rfc-editor.org/rfc/rfc8247#section-2.4
diff --git a/src/crypto/crypto_cipher.cc b/src/crypto/crypto_cipher.cc
index 8cc2b1786c98b9..fae5b608062422 100644
--- a/src/crypto/crypto_cipher.cc
+++ b/src/crypto/crypto_cipher.cc
@@ -697,6 +697,19 @@ void CipherBase::SetAuthTag(const FunctionCallbackInfo<Value>& args) {
       env, "Invalid authentication tag length: %u", tag_len);
   }
 
+  if (mode == EVP_CIPH_GCM_MODE && cipher->auth_tag_len_ == kNoAuthTagLength &&
+      tag_len != 16 && env->options()->pending_deprecation &&
+      env->EmitProcessEnvWarning()) {
+    if (ProcessEmitDeprecationWarning(
+            env,
+            "Using AES-GCM authentication tags of less than 128 bits without "
+            "specifying the authTagLength option when initializing decryption "
+            "is deprecated.",
+            "DEP0182")
+            .IsNothing())
+      return;
+  }
+
   cipher->auth_tag_len_ = tag_len;
   cipher->auth_tag_state_ = kAuthTagKnown;
   CHECK_LE(cipher->auth_tag_len_, sizeof(cipher->auth_tag_));
diff --git a/test/parallel/test-crypto-gcm-decipheriv-short-tag.js b/test/parallel/test-crypto-gcm-decipheriv-short-tag.js
new file mode 100644
index 00000000000000..0776506bb63523
--- /dev/null
+++ b/test/parallel/test-crypto-gcm-decipheriv-short-tag.js
@@ -0,0 +1,21 @@
+// Flags: --pending-deprecation
+'use strict';
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const { createDecipheriv, randomBytes } = require('crypto');
+
+common.expectWarning({
+  DeprecationWarning: [
+    ['Using AES-GCM authentication tags of less than 128 bits without ' +
+     'specifying the authTagLength option when initializing decryption is ' +
+     'deprecated.',
+     'DEP0182'],
+  ]
+});
+
+const key = randomBytes(32);
+const iv = randomBytes(16);
+const tag = randomBytes(12);
+createDecipheriv('aes-256-gcm', key, iv).setAuthTag(tag);