1 files changed, 42 insertions, 0 deletions
diff --git a/src/main/model/asn1/TagClass.java b/src/main/model/asn1/TagClass.java
new file mode 100644
index 0000000..83dd4e9
--- /dev/null
+++ b/src/main/model/asn1/TagClass.java
@@ -0,0 +1,42 @@
+package model.asn1;
+
+/**
+ * Represents the class (UNIVERSAL, APPLICATION, PRIVATE, CONTEXT-SPECIFIC) of an ASN.1 tag. See X.680$8.1.
+ * The purpose of UNIVERSAL, APPLICATION, PRIVATE, and CONTEXT_SPECIFIC can be found in X.680 spec.
+ * For example, UNIVERSAL means tags specified in the core ASN.1 spec.
+ * This class also represents the value to the two highest bits of DER-encoded tag values.
+ */
+public enum TagClass {
+    UNIVERSAL(Values.UNIVERSAL),
+    APPLICATION(Values.APPLICATION),
+    PRIVATE(Values.PRIVATE),
+    CONTEXT_SPECIFIC(Values.CONTENT_SPECIFIC);
+
+    private final Byte val;
+
+    /**
+     * EFFECT: Constructs the tag class with the given DER tag byte value.
+     * REQUIRES: The Byte value must have low 6bits cleared.
+     */
+    TagClass(Byte val) {
+        this.val = val;
+    }
+
+    public Byte getVal() {
+        return val;
+    }
+
+    /**
+     * The constants of high-two-bit values for Tag DER encoding.
+     */
+    public static final class Values {
+        // 0b00000000
+        public static final Byte UNIVERSAL = 0x0;
+        // 0b01000000
+        public static final Byte APPLICATION = 0x40;
+        // 0b11000000
+        public static final Byte PRIVATE = -64;
+        // 0b10000000
+        public static final Byte CONTENT_SPECIFIC = -128;
+    }
+}