<?php
namespace Activitypub;
use DateTime;
use DateTimeZone;
/**
* ActivityPub Signature Class
*
* @author Matthias Pfefferle
*/
class Signature {
/**
* @param int $user_id
*
* @return mixed
*/
public static function get_public_key( $user_id, $force = false ) {
if ( $force ) {
self::generate_key_pair( $user_id );
}
if ( -1 === $user_id ) {
$key = array( \get_option( 'activitypub_magic_sig_public_key' ) );
} else {
$key = \get_user_meta( $user_id, 'magic_sig_public_key' );
}
return $key[0];
}
/**
* @param int $user_id
*
* @return mixed
*/
public static function get_private_key( $user_id, $force = false ) {
if ( $force ) {
self::generate_key_pair( $user_id );
}
if ( -1 === $user_id ) {
$key = \get_option( 'activitypub_magic_sig_private_key' );
} else {
$key = \get_user_meta( $user_id, 'magic_sig_private_key' );
}
return $key[0];
}
/**
* Generates the pair keys
*
* @param int $user_id
*/
public static function generate_key_pair( $user_id ) {
$config = array(
'digest_alg' => 'sha512',
'private_key_bits' => 2048,
'private_key_type' => \OPENSSL_KEYTYPE_RSA,
);
$key = \openssl_pkey_new( $config );
$priv_key = null;
\openssl_pkey_export( $key, $priv_key );
$detail = \openssl_pkey_get_details( $key );
if ( -1 === $user_id ) {
// private key
\add_option( 'activitypub_magic_sig_private_key', $priv_key );
// public key
\add_option( 'activitypub_magic_sig_public_key', $detail['key'] );
} else {
// private key
\update_user_meta( $user_id, 'magic_sig_private_key', $priv_key );
// public key
\update_user_meta( $user_id, 'magic_sig_public_key', $detail['key'] );
}
}
public static function generate_signature( $user_id, $http_method, $url, $date, $digest = null ) {
$key = self::get_private_key( $user_id );
$url_parts = \wp_parse_url( $url );
$host = $url_parts['host'];
$path = '/';
// add path
if ( ! empty( $url_parts['path'] ) ) {
$path = $url_parts['path'];
}
// add query
if ( ! empty( $url_parts['query'] ) ) {
$path .= '?' . $url_parts['query'];
}
if ( ! empty( $digest ) ) {
$signed_string = "(request-target): $http_method $path\nhost: $host\ndate: $date\ndigest: SHA-256=$digest";
} else {
$signed_string = "(request-target): $http_method $path\nhost: $host\ndate: $date";
}
$signature = null;
\openssl_sign( $signed_string, $signature, $key, \OPENSSL_ALGO_SHA256 );
$signature = \base64_encode( $signature ); // phpcs:ignore
if ( -1 === $user_id ) {
$key_id = \get_rest_url( null, 'activitypub/1.0/service#main-key' );
} else {
$key_id = \get_author_posts_url( $user_id ) . '#main-key';
}
if ( ! empty( $digest ) ) {
return \sprintf( 'keyId="%s",algorithm="rsa-sha256",headers="(request-target) host date digest",signature="%s"', $key_id, $signature );
} else {
return \sprintf( 'keyId="%s",algorithm="rsa-sha256",headers="(request-target) host date",signature="%s"', $key_id, $signature );
}
}
/**
* Verifies the http signatures
*
* @param WP_REQUEST | Array $_SERVER
* @return void
* @author Django Doucet
*/
public static function verify_http_signature( $request ) {
if ( is_object( $request ) ) { // REST Request object
$headers = $request->get_headers();
$actor = isset( json_decode( $request->get_body() )->actor ) ? json_decode( $request->get_body() )->actor : '';
$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' /wp-json' . $request->get_route();
} else {
$request = self::format_server_request( $request );
$headers = $request['headers']; // $_SERVER array
$headers['(request-target)'][0] = strtolower( $headers['request_method'][0] ) . ' ' . $headers['request_uri'][0];
$actor = '';
}
if ( ! isset( $headers['signature'] ) ) {
return new \WP_Error( 'activitypub_signature', 'Request not signed', array( 'status' => 403 ) );
}
if ( array_key_exists( 'signature', $headers ) ) {
$signature_block = self::parse_signature_header( $headers['signature'] );
} elseif ( array_key_exists( 'authorization', $headers ) ) {
$signature_block = self::parse_signature_header( $headers['authorization'] );
}
if ( ! isset( $signature_block ) || ! $signature_block ) {
return new \WP_Error( 'activitypub_signature', 'Incompatible request signature. keyId and signature are required', array( 'status' => 403 ) );
}
$signed_headers = $signature_block['headers'];
if ( ! $signed_headers ) {
$signed_headers = array( 'date' );
}
$signed_data = self::get_signed_data( $signed_headers, $signature_block, $headers );
if ( ! $signed_data ) {
return new \WP_Error( 'activitypub_signature', 'Signed request date outside acceptable time window', array( 'status' => 403 ) );
}
$algorithm = self::get_signature_algorithm( $signature_block );
if ( ! $algorithm ) {
return new \WP_Error( 'activitypub_signature', 'Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)', array( 'status' => 403 ) );
}
if ( \in_array( 'digest', $signed_headers, true ) && isset( $body ) ) {
if ( is_array( $headers['digest'] ) ) {
$headers['digest'] = $headers['digest'][0];
}
$digest = explode( '=', $headers['digest'], 2 );
if ( 'SHA-256' === $digest[0] ) {
$hashalg = 'sha256';
}
if ( 'SHA-512' === $digest[0] ) {
$hashalg = 'sha512';
}
if ( \base64_encode( \hash( $hashalg, $body, true ) ) !== $digest[1] ) { // phpcs:ignore
return new \WP_Error( 'activitypub_signature', 'Invalid Digest header', array( 'status' => 403 ) );
}
}
$public_key = \Activitypub\get_remote_metadata_by_actor( strtok( strip_fragment_from_url( $signature_block['keyId'] ), '?' ) ); // phpcs:ignore
if ( \is_wp_error( $public_key ) ) {
return $public_key;
} else {
$public_key = \rtrim( $public_key );
}
$verified = \openssl_verify( $signed_data, $signature_block['signature'], $public_key, $algorithm ) > 0;
if ( ! $verified ) {
return new \WP_Error( 'activitypub_signature', 'Invalid signature', array( 'status' => 403 ) );
}
return $verified;
}
/**
* Gets the signature algorithm from the signature header
*
* @param array $signature_block
* @return string algorithm
* @author Django Doucet
*/
public static function get_signature_algorithm( $signature_block ) {
if ( $signature_block['algorithm'] ) {
switch ( $signature_block['algorithm'] ) {
case 'rsa-sha-512':
return 'sha512'; //hs2019 https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12
default:
return 'sha256';
}
}
return false;
}
/**
* Parses the Signature header
*
* @param array $header
* @return array signature parts
* @author Django Doucet
*/
public static function parse_signature_header( $header ) {
$ret = array();
$matches = array();
$h_string = \implode( ',', (array) $header[0] );
if ( \preg_match( '/keyId="(.*?)"/ism', $h_string, $matches ) ) {
$ret['keyId'] = $matches[1];
}
if ( \preg_match( '/created=([0-9]*)/ism', $h_string, $matches ) ) {
$ret['(created)'] = $matches[1];
}
if ( \preg_match( '/expires=([0-9]*)/ism', $h_string, $matches ) ) {
$ret['(expires)'] = $matches[1];
}
if ( \preg_match( '/algorithm="(.*?)"/ism', $h_string, $matches ) ) {
$ret['algorithm'] = $matches[1];
}
if ( \preg_match( '/headers="(.*?)"/ism', $h_string, $matches ) ) {
$ret['headers'] = \explode( ' ', $matches[1] );
}
if ( \preg_match( '/signature="(.*?)"/ism', $h_string, $matches ) ) {
$ret['signature'] = \base64_decode( preg_replace( '/\s+/', '', $matches[1] ) ); // phpcs:ignore
}
if ( ( $ret['signature'] ) && ( $ret['algorithm'] ) && ( ! $ret['headers'] ) ) {
$ret['headers'] = array( 'date' );
}
return $ret;
}
/**
* Gets the header data from the included pseudo headers
*
* @param array $signed_headers
* @param array $signature_block (pseudo-headers)
* @param array $headers (http headers)
* @return signed headers for comparison
* @author Django Doucet
*/
public static function get_signed_data( $signed_headers, $signature_block, $headers ) {
$signed_data = '';
// This also verifies time-based values by returning false if any of these are out of range.
foreach ( $signed_headers as $header ) {
if ( \array_key_exists( $header, $headers ) ) {
if ( 'host' === $header ) {
if ( isset( $headers['x_original_host'] ) ) {
$signed_data .= $header . ': ' . $headers['x_original_host'][0] . "\n";
} else {
$signed_data .= $header . ': ' . $headers[ $header ][0] . "\n";
}
} else {
$signed_data .= $header . ': ' . $headers[ $header ][0] . "\n";
}
}
if ( '(created)' === $header ) {
if ( ! empty( $signature_block['(created)'] ) && \intval( $signature_block['(created)'] ) > \time() ) {
// created in future
return false;
}
$signed_data .= '(created): ' . $signature_block['(created)'] . "\n";
}
if ( '(expires)' === $header ) {
if ( ! empty( $signature_block['(expires)'] ) && \intval( $signature_block['(expires)'] ) < \time() ) {
// expired in past
return false;
}
$signed_data .= '(expires): ' . $signature_block['(expires)'] . "\n";
}
if ( 'content-type' === $header ) {
$signed_data .= $header . ': ' . $headers['content_type'][0] . "\n";
}
if ( 'content-length' === $header ) {
$signed_data .= $header . ': ' . $headers['content_length'][0] . "\n";
}
if ( 'date' === $header ) {
// allow a bit of leeway for misconfigured clocks.
$d = new DateTime( $headers[ $header ][0] );
$d->setTimeZone( new DateTimeZone( 'UTC' ) );
$c = $d->format( 'U' );
$dplus = time() + ( 3 * HOUR_IN_SECONDS );
$dminus = time() - ( 3 * HOUR_IN_SECONDS );
if ( $c > $dplus || $c < $dminus ) {
// time out of range
return false;
}
}
}
return \rtrim( $signed_data, "\n" );
}
public static function generate_digest( $body ) {
$digest = \base64_encode( \hash( 'sha256', $body, true ) ); // phpcs:ignore
return "$digest";
}
/**
* Formats the $_SERVER to resemble the WP_REST_REQUEST array,
* for use with verify_http_signature()
*
* @param array $_SERVER
* @return array $request
*/
public static function format_server_request( $server ) {
$request = array();
foreach ( $server as $param_key => $param_val ) {
$req_param = strtolower( $param_key );
if ( 'REQUEST_URI' === $req_param ) {
$request['headers']['route'][] = $param_val;
} else {
$header_key = str_replace(
'http_',
'',
$req_param
);
$request['headers'][ $header_key ][] = \wp_unslash( $param_val );
}
}
return $request;
}
}