return gzinflate( substr( $data, 10, -8 ) );
}
}
+
+// hash_equals function only exists in PHP >= 5.6.0
+if ( !function_exists( 'hash_equals' ) ) {
+ /**
+ * Check whether a user-provided string is equal to a fixed-length secret without
+ * revealing bytes of the secret through timing differences.
+ *
+ * This timing guarantee -- that a partial match takes the same time as a complete
+ * mismatch -- is why this function is used in some security-sensitive parts of the code.
+ * For example, it shouldn't be possible to guess an HMAC signature one byte at a time.
+ *
+ * Longer explanation: http://www.emerose.com/timing-attacks-explained
+ *
+ * @codeCoverageIgnore
+ * @param string $known_string Fixed-length secret to compare against
+ * @param string $user_string User-provided string
+ * @return bool True if the strings are the same, false otherwise
+ */
+ function hash_equals( $known_string, $user_string ) {
+ // Strict type checking as in PHP's native implementation
+ if ( !is_string( $known_string ) ) {
+ trigger_error( 'hash_equals(): Expected known_string to be a string, ' .
+ gettype( $known_string ) . ' given', E_USER_WARNING );
+
+ return false;
+ }
+
+ if ( !is_string( $user_string ) ) {
+ trigger_error( 'hash_equals(): Expected user_string to be a string, ' .
+ gettype( $user_string ) . ' given', E_USER_WARNING );
+
+ return false;
+ }
+
+ // Note that we do one thing PHP doesn't: try to avoid leaking information about
+ // relative lengths of $known_string and $user_string, and of multiple $known_strings.
+ // However, lengths may still inevitably leak through, for example, CPU cache misses.
+ $known_string_len = strlen( $known_string );
+ $user_string_len = strlen( $user_string );
+ $result = $known_string_len ^ $user_string_len;
+ for ( $i = 0; $i < $user_string_len; $i++ ) {
+ $result |= ord( $known_string[$i % $known_string_len] ) ^ ord( $user_string[$i] );
+ }
+
+ return ( $result === 0 );
+ }
+}
/// @endcond
/**