Support ASN.1 tag encoding with values greater than 30.

This follows [https://www.oss.com/asn1/resources/asn1-made-simple/asn1-quick-reference/basic-encoding-rules.html](https://www.oss.com/asn1/resources/asn1-made-simple/asn1-quick-reference/basic-encoding-rules.html)
terrafrost · Jan 24, 2025 · a02712f · a02712f
1 parent 658ee70
commit a02712f
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diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
@@ -931,7 +931,19 @@ private static function encode_der($source, array $mapping, $idx = null, array $
                             an untagged "DummyReference" (see ITU-T Rec. X.683 | ISO/IEC 8824-4, 8.3)."
                          */
                         if (isset($child['explicit']) || $child['type'] == self::TYPE_CHOICE) {
-                            $subtag = chr((self::CLASS_CONTEXT_SPECIFIC << 6) | 0x20 | $child['constant']);
+                            if ($child['constant'] <= 30) {
+                                $subtag = chr((self::CLASS_CONTEXT_SPECIFIC << 6) | 0x20 | $child['constant']);
+                            } else {
+                                $constant = $child['constant'];
+                                $subtag = '';
+                                while ($constant > 0) {
+                                    $subtagvalue = $constant & 0x7F;
+                                    $subtag = (chr(0x80 | $subtagvalue)) . $subtag;
+                                    $constant = $constant >> 7;
+                                }
+                                $subtag[strlen($subtag) - 1] = $subtag[strlen($subtag) - 1] & chr(0x7F);
+                                $subtag = chr((self::CLASS_CONTEXT_SPECIFIC << 6) | 0x20 | 0x1f) . $subtag;
+                            }
                             $temp = $subtag . self::encodeLength(strlen($temp)) . $temp;
                         } else {
                             $subtag = chr((self::CLASS_CONTEXT_SPECIFIC << 6) | (ord($temp[0]) & 0x20) | $child['constant']);

diff --git a/tests/Unit/File/ASN1Test.php b/tests/Unit/File/ASN1Test.php
@@ -343,6 +343,32 @@ public function testApplicationTag()
         $this->assertSame($data, $arr);
     }
 
+    public function testBigApplicationTag(): void
+    {
+        $map = [
+            'type'     => ASN1::TYPE_SEQUENCE,
+            'children' => [
+                'demo' => [
+                    'constant' => 0xFFFFFFFF,
+                    'optional' => true,
+                    'explicit' => true,
+                    'default'  => 'v1',
+                    'type'     => ASN1::TYPE_INTEGER,
+                    'mapping' => ['v1', 'v2', 'v3'],
+                ],
+            ],
+        ];
+
+        $data = ['demo' => 'v3'];
+
+        $str = ASN1::encodeDER($data, $map);
+
+        $decoded = ASN1::decodeBER($str);
+        $arr = ASN1::asn1map($decoded[0], $map);
+
+        $this->assertSame($data, $arr);
+    }
+
     /**
      * @group github1296
      */