From 2d2cef01fbf0f8d1891d00b7e31dd6d02398ac8c Mon Sep 17 00:00:00 2001
From: Vladimir Asantsev <51046969+tawnysoul28@users.noreply.github.com>
Date: Sat, 15 Aug 2026 18:17:20 +0700
Subject: [PATCH] typeClass() misidentifies `private` class (0xC0) tags as
 `application`
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`ASN1Identifier.typeClass()` never returns `.private`, even for tag bytes
where both class bits are set (`11`, i.e. the `private` class). Such bytes
are always misclassified as `.application` instead.

**Root cause**

```swift
public func typeClass() -> Class {
    for tc in [Class.application, Class.contextSpecific, Class.private] where (rawValue & tc.rawValue) == tc.rawValue {
        return tc
    }
    return .universal
}
```

The loop checks `.application` (`0x40`) before `.private` (`0xC0`). The
check `(rawValue & 0x40) == 0x40` only tests whether bit `0x40` is set — it
does not exclude the case where bit `0x80` is *also* set. Since
`0xC0 & 0x40 == 0x40`, any byte with both class bits set satisfies the
`.application` condition first, and the loop returns before ever reaching
`.private`.

**Reproduction**

```swift
ASN1Identifier(rawValue: 0xC1).typeClass()
// Actual:   .application
// Expected: .private
```

**Suggested fix**

Since `Class`'s raw values already occupy the full 2-bit space (`0x00`,
`0x40`, `0x80`, `0xC0`), a single mask-and-lookup replaces the loop:

```swift
public func typeClass() -> Class {
    return Class(rawValue: rawValue & 0xC0) ?? .universal
}
```

Happy to open a PR with this change if useful.
---
 ASN1Decoder/ASN1Identifier.swift | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/ASN1Decoder/ASN1Identifier.swift b/ASN1Decoder/ASN1Identifier.swift
index 318a366..c2855fb 100644
--- a/ASN1Decoder/ASN1Identifier.swift
+++ b/ASN1Decoder/ASN1Identifier.swift
@@ -73,10 +73,7 @@ public class ASN1Identifier: CustomStringConvertible {
     }
 
     public func typeClass() -> Class {
-        for tc in [Class.application, Class.contextSpecific, Class.private] where (rawValue & tc.rawValue) == tc.rawValue {
-            return tc
-        }
-        return .universal
+        return Class(rawValue: rawValue & 0xC0) ?? .universal
     }
 
     public func isPrimitive() -> Bool {