diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index 3d49d45e..cf3fe501 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -268,9 +268,10 @@ abstract class ASN1
             $tag = 0;
             // process septets (since the eighth bit is ignored, it's not an octet)
             do {
-                $loop = ord($encoded[0]) >> 7;
+                $temp = ord($encoded[$encoded_pos++]);
+                $loop = $temp >> 7;
                 $tag <<= 7;
-                $tag |= ord($encoded[$encoded_pos++]) & 0x7F;
+                $tag |= $temp & 0x7F;
                 $start++;
             } while ($loop);
         }
diff --git a/phpseclib/Math/BigInteger/Engines/Engine.php b/phpseclib/Math/BigInteger/Engines/Engine.php
index 9b6c0655..39b641cf 100644
--- a/phpseclib/Math/BigInteger/Engines/Engine.php
+++ b/phpseclib/Math/BigInteger/Engines/Engine.php
@@ -145,7 +145,7 @@ abstract class Engine implements \Serializable
                 // (?<=^|-)0*: find any 0's that are preceded by the start of the string or by a - (ie. octals)
                 // [^-0-9].*: find any non-numeric characters and then any characters that follow that
                 $this->value = preg_replace('#(?<!^)(?:-).*|(?<=^|-)0*|[^-0-9].*#', '', $x);
-                if (!strlen($this->value)) {
+                if (!strlen($this->value) || $this->value == '-') {
                     $this->value = '0';
                 }
                 static::initialize($base);
diff --git a/phpseclib/Math/BigInteger/Engines/GMP.php b/phpseclib/Math/BigInteger/Engines/GMP.php
index 333829c1..262e55c2 100644
--- a/phpseclib/Math/BigInteger/Engines/GMP.php
+++ b/phpseclib/Math/BigInteger/Engines/GMP.php
@@ -296,7 +296,14 @@ class GMP extends Engine
      */
     public function compare(GMP $y)
     {
-        return gmp_cmp($this->value, $y->value);
+        $r = gmp_cmp($this->value, $y->value);
+        if ($r < -1) {
+            $r = -1;
+        }
+        if ($r > 1) {
+            $r = 1;
+        }
+        return $r;
     }
 
     /**
diff --git a/tests/Unit/File/X509/X509Test.php b/tests/Unit/File/X509/X509Test.php
index 23baed42..4da2300f 100644
--- a/tests/Unit/File/X509/X509Test.php
+++ b/tests/Unit/File/X509/X509Test.php
@@ -856,5 +856,23 @@ wkwhE/JaQAEHq2PHnEmvwyBiJcHSdLXkcLzYlg19Ho0BPqVKdulx8GAk
 
         $r = $x509->loadX509($result);
         $this->assertArrayHasKey('tbsCertificate', $r);
+
+    public function testLongTagOnBadCert()
+    {
+        // the problem with this cert is that it'd cause an infinite loop
+        $x509 = new X509();
+        $r = @$x509->loadX509('-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----');
+
+        $this->assertFalse($r);
     }
 }
diff --git a/tests/Unit/Math/BigInteger/TestCase.php b/tests/Unit/Math/BigInteger/TestCase.php
index 800258b2..f8697e4e 100644
--- a/tests/Unit/Math/BigInteger/TestCase.php
+++ b/tests/Unit/Math/BigInteger/TestCase.php
@@ -178,6 +178,9 @@ abstract class Unit_Math_BigInteger_TestCase extends PhpseclibTestCase
         // c < d
         $this->assertLessThan(0, $c->compare($d));
         $this->assertGreaterThan(0, $d->compare($c));
+
+        $this->assertSame(-1, $this->getInstance(-999)->compare($this->getInstance(370)));
+        $this->assertSame(1, $this->getInstance(999)->compare($this->getInstance(-700)));
     }
 
     public function testBitwiseAND()
@@ -457,4 +460,13 @@ abstract class Unit_Math_BigInteger_TestCase extends PhpseclibTestCase
         $temp = $this->getInstance(48);
         $this->assertSame($temp->toHex(true), '30');
     }
+
+    public function testZeroBase10()
+    {
+        $temp = $this->getInstance('00');
+        $this->assertSame($temp->toString(), '0');
+
+        $temp = $this->getInstance('-0');
+        $this->assertSame($temp->toString(), '0');
+    }
 }