wordpress-seo / src / myyoast-client / infrastructure / crypto / key-pair-manager.php

key-pair-manager.php in Yoast SEO – Advanced SEO with real-time guidance and built-in AI 27.7, at src/myyoast-client/infrastructure/crypto/key-pair-manager.php

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1	<?php
2	// phpcs:disable Yoast.NamingConventions.NamespaceName.TooLong -- Needed in the folder structure.
3
4	namespace Yoast\WP\SEO\MyYoast_Client\Infrastructure\Crypto;
5
6	use SodiumException;
7	use Yoast\WP\SEO\MyYoast_Client\Infrastructure\Encoding\Base64url;
8	use Yoast\WP\SEO\MyYoast_Client\Infrastructure\OIDC\Issuer_Config;
9	use YoastSEO_Vendor\Psr\Log\LoggerAwareInterface;
10	use YoastSEO_Vendor\Psr\Log\LoggerAwareTrait;
11	use YoastSEO_Vendor\Psr\Log\NullLogger;
12
13	/**
14	* Manages Ed25519 key pairs for DPoP proofs and private_key_jwt authentication.
15	*
16	* Generates, stores (encrypted), retrieves, and rotates key pairs.
17	* Two independent key pairs are maintained:
18	* - 'registration': for private_key_jwt client_assertion signing
19	* - 'dpop': for DPoP proof signing
20	*/
21	class Key_Pair_Manager implements LoggerAwareInterface {
22	use LoggerAwareTrait;
23
24	public const PURPOSE_REGISTRATION = 'registration';
25	public const PURPOSE_DPOP = 'dpop';
26
27	private const OPTION_PREFIX = 'wpseo_myyoast_key_pair_';
28	private const CONTEXT_PREFIX = 'yoast-myyoast-key-';
29
30	private const JWK_KTY = 'OKP';
31	private const JWK_CRV = 'Ed25519';
32	private const JWK_ALG = 'EdDSA';
33
34	/**
35	* The encryption service.
36	*
37	* @var Encryption
38	*/
39	private $encryption;
40
41	/**
42	* The issuer configuration.
43	*
44	* @var Issuer_Config
45	*/
46	private $issuer_config;
47
48	/**
49	* In-memory cache for decrypted key pairs, keyed by purpose.
50	*
51	* @var array<string, Key_Pair\|null>
52	*/
53	private $cached_key_pairs = [];
54
55	/**
56	* Key_Pair_Manager constructor.
57	*
58	* @param Encryption $encryption The encryption service.
59	* @param Issuer_Config $issuer_config The issuer configuration.
60	*/
61	public function __construct( Encryption $encryption, Issuer_Config $issuer_config ) {
62	$this->encryption = $encryption;
63	$this->issuer_config = $issuer_config;
64	$this->logger = new NullLogger();
65	}
66
67	/**
68	* Gets an existing key pair or creates a new one for the given purpose.
69	* Creates a new key pair if none exists or if decryption of the stored private key fails (e.g. due to corruption or missing/rotated key).
70	*
71	* @param string $purpose One of the PURPOSE_* constants.
72	*
73	* @return Key_Pair The key pair value object.
74	*
75	* @throws Encryption_Exception If encryption fails.
76	*/
77	public function get_or_create_key_pair( string $purpose ): Key_Pair {
78	$option_key = $this->get_option_key( $purpose );
79	if ( \array_key_exists( $option_key, $this->cached_key_pairs ) ) {
80	$cached = $this->cached_key_pairs[ $option_key ];
81	if ( $cached !== null ) {
82	return $cached;
83	}
84
85	return $this->generate_and_store_key_pair( $purpose );
86	}
87
88	try {
89	$stored = $this->get_stored_key_pair( $purpose );
90	} catch ( Encryption_Exception $e ) {
91	$this->logger->warning(
92	'Failed to decrypt {purpose} key pair, auto-rotating: {error}',
93	[
94	'purpose' => $purpose,
95	'error' => $e->getMessage(),
96	],
97	);
98	return $this->rotate_key_pair( $purpose );
99	}
100
101	return ( $stored ?? $this->generate_and_store_key_pair( $purpose ) );
102	}
103
104	/**
105	* Generates a new key pair, replacing any existing one for the given purpose.
106	*
107	* @param string $purpose One of the PURPOSE_* constants.
108	*
109	* @return Key_Pair The key pair value object.
110	*
111	* @throws Encryption_Exception If encryption fails.
112	*/
113	public function rotate_key_pair( string $purpose ): Key_Pair {
114	return $this->generate_and_store_key_pair( $purpose );
115	}
116
117	/**
118	* Returns the public key as a JWK (JSON Web Key) for the given key pair.
119	*
120	* @param Key_Pair $key_pair The key pair to extract the public JWK from.
121	*
122	* @return array<string, string> The JWK array with kty, crv, x, kid, use, and alg fields.
123	*/
124	public function get_public_key_jwk( Key_Pair $key_pair ): array {
125	return [
126	'kty' => self::JWK_KTY,
127	'crv' => self::JWK_CRV,
128	'x' => Base64url::encode( $key_pair->get_public_key() ),
129	'kid' => $key_pair->get_kid(),
130	'use' => 'sig',
131	'alg' => self::JWK_ALG,
132	];
133	}
134
135	/**
136	* Generates a new Ed25519 key pair in memory without persisting it.
137	*
138	* Use store_key_pair() to persist after confirming success of external operations.
139	*
140	* @return Key_Pair The generated key pair.
141	*
142	* @throws Encryption_Exception If key generation fails.
143	*/
144	public function generate_key_pair(): Key_Pair {
145	$keypair = '';
146
147	try {
148	$keypair = \sodium_crypto_sign_keypair();
149	$public_key = \sodium_crypto_sign_publickey( $keypair );
150	$private_key = \sodium_crypto_sign_secretkey( $keypair );
151	$kid = Base64url::encode( \hash( 'sha256', $public_key, true ) );
152
153	return new Key_Pair( $public_key, $private_key, $kid );
154	}
155	catch ( SodiumException $e ) {
156	// phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Internal exception message.
157	throw new Encryption_Exception( 'Key pair generation failed: ' . $e->getMessage(), 0, $e );
158	}
159	finally {
160	if ( $keypair !== '' ) {
161	try {
162	\sodium_memzero( $keypair );
163	}
164	catch ( SodiumException $e ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch -- Best-effort cleanup.
165	// Best-effort: keypair will be freed when it goes out of scope.
166	}
167	}
168	}
169	}
170
171	/**
172	* Builds a JWK from a raw public key without requiring it to be stored.
173	*
174	* @param string $public_key The 32-byte Ed25519 public key.
175	*
176	* @return array<string, string> The JWK array.
177	*/
178	public function build_public_key_jwk( string $public_key ): array {
179	$kid = Base64url::encode( \hash( 'sha256', $public_key, true ) );
180
181	return [
182	'kty' => self::JWK_KTY,
183	'crv' => self::JWK_CRV,
184	'x' => Base64url::encode( $public_key ),
185	'kid' => $kid,
186	'use' => 'sig',
187	'alg' => self::JWK_ALG,
188	];
189	}
190
191	/**
192	* Persists a key pair (encrypting the private key).
193	*
194	* @param string $purpose One of the PURPOSE_* constants.
195	* @param Key_Pair $key_pair The key pair to store.
196	*
197	* @return void
198	*
199	* @throws Encryption_Exception If encryption fails.
200	*/
201	public function store_key_pair( string $purpose, Key_Pair $key_pair ): void {
202	$option_key = $this->get_option_key( $purpose );
203	$encrypted_private = $this->encryption->encrypt(
204	$key_pair->get_private_key(),
205	self::CONTEXT_PREFIX . $purpose,
206	);
207
208	\update_option(
209	$option_key,
210	[
211	// phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode -- Binary Ed25519 key needs safe encoding.
212	'public_key' => \base64_encode( $key_pair->get_public_key() ),
213	'private_key_encrypted' => $encrypted_private,
214	'kid' => $key_pair->get_kid(),
215	'created_at' => \time(),
216	],
217	false,
218	);
219	$this->cached_key_pairs[ $option_key ] = $key_pair;
220	}
221
222	/**
223	* Deletes the key pair for the given purpose.
224	*
225	* @param string $purpose One of the PURPOSE_* constants.
226	*
227	* @return void
228	*/
229	public function delete_key_pair( string $purpose ): void {
230	unset( $this->cached_key_pairs[ $this->get_option_key( $purpose ) ] );
231	\delete_option( $this->get_option_key( $purpose ) );
232	}
233
234	/**
235	* Returns the issuer-scoped option key for the given purpose.
236	*
237	* @param string $purpose One of the PURPOSE_* constants.
238	*
239	* @return string The option key.
240	*/
241	private function get_option_key( string $purpose ): string {
242	return self::OPTION_PREFIX . $purpose . '_' . $this->issuer_config->get_issuer_key();
243	}
244
245	/**
246	* Retrieves a stored key pair, decrypting the private key.
247	*
248	* @param string $purpose One of the PURPOSE_* constants.
249	*
250	* @return Key_Pair\|null The key pair or null if not stored.
251	*
252	* @throws Encryption_Exception If decryption fails.
253	*/
254	private function get_stored_key_pair( string $purpose ): ?Key_Pair {
255	$stored = \get_option( $this->get_option_key( $purpose ), [] );
256	if ( ! \is_array( $stored ) \|\| empty( $stored['public_key'] ) \|\| empty( $stored['private_key_encrypted'] ) \|\| empty( $stored['kid'] ) ) {
257	$this->cached_key_pairs[ $this->get_option_key( $purpose ) ] = null;
258	return null;
259	}
260
261	// phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode -- Decoding our own base64-encoded key.
262	$public_key = \base64_decode( $stored['public_key'], true );
263	$private_key = $this->encryption->decrypt(
264	$stored['private_key_encrypted'],
265	self::CONTEXT_PREFIX . $purpose,
266	);
267
268	if ( $public_key === false \|\| \strlen( $public_key ) !== \SODIUM_CRYPTO_SIGN_PUBLICKEYBYTES ) {
269	$this->cached_key_pairs[ $this->get_option_key( $purpose ) ] = null;
270	return null;
271	}
272
273	$key_pair = new Key_Pair( $public_key, $private_key, $stored['kid'] );
274	$this->cached_key_pairs[ $this->get_option_key( $purpose ) ] = $key_pair;
275	return $key_pair;
276	}
277
278	/**
279	* Generates a new Ed25519 key pair and stores it (private key encrypted).
280	*
281	* @param string $purpose One of the PURPOSE_* constants.
282	*
283	* @return Key_Pair The key pair value object.
284	*
285	* @throws Encryption_Exception If encryption or key generation fails.
286	*/
287	private function generate_and_store_key_pair( string $purpose ): Key_Pair {
288	$key_pair = $this->generate_key_pair();
289	$this->store_key_pair( $purpose, $key_pair );
290	$this->logger->info( 'Generated and stored new {purpose} key pair.', [ 'purpose' => $purpose ] );
291
292	return $key_pair;
293	}
294	}
295