From d342a45d98c4795b3a3fe1aaef5236ad4a782b55 Mon Sep 17 00:00:00 2001
From: Yuuta Liang <yuutaw@students.cs.ubc.ca>
Date: Thu, 12 Oct 2023 12:10:33 +0800
Subject: Implement data structures from X.680, X.501, X.509, and PKCS#10, with
 X.690 encoding / decoding support

The implementation took four days, and it is still a little bit rough. Updated version should arrive soon.

Signed-off-by: Yuuta Liang <yuutaw@students.cs.ubc.ca>
---
 src/main/model/asn1/Int.java | 81 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 src/main/model/asn1/Int.java

(limited to 'src/main/model/asn1/Int.java')

diff --git a/src/main/model/asn1/Int.java b/src/main/model/asn1/Int.java
new file mode 100644
index 0000000..5b75a73
--- /dev/null
+++ b/src/main/model/asn1/Int.java
@@ -0,0 +1,81 @@
+package model.asn1;
+
+import model.asn1.exceptions.ParseException;
+import model.asn1.parsing.BytesReader;
+import model.pki.cert.TbsCertificate;
+import ui.Utils;
+
+import java.math.BigInteger;
+import java.util.Arrays;
+
+/**
+ * An ASN.1 INTEGER type. By spec, it can be arbitrarily long. But just like it's impossible to have an
+ * endless tape in a turing machine, this implementation uses fixed length internally to represent ints.
+ */
+public class Int extends ASN1Object {
+    /**
+     * The X.680 universal class tag assignment.
+     */
+    public static final Tag TAG = new Tag(TagClass.UNIVERSAL, false, 0x2);
+
+    private final BigInteger value;
+
+    /**
+     * EFFECTS: Initiate the INTEGER object with the given tag and an optional context-specific tag number for explicit
+     * encoding. For more information, consult {@link ASN1Object}.
+     * REQUIRES: Consult {@link ASN1Object}.
+     */
+    public Int(Tag tag, Tag parentTag, long value) {
+        super(tag, parentTag);
+        this.value = BigInteger.valueOf(value);
+    }
+
+    /**
+     * EFFECTS: Parse input and get the int value. Tags are parsed in {@link ASN1Object}.
+     *   Throws {@link  ParseException} if encoded value are invalid:
+     *     - Early EOF (not enough bytes)
+     *     - Zero bytes length
+     *     - Other issues denoted in {@link ASN1Object}
+     * MODIFIES: this, encoded
+     */
+    public Int(BytesReader encoded, boolean hasParentTag) throws ParseException {
+        super(encoded, hasParentTag);
+        if (getLength() == 0) {
+            throw new ParseException("Integer with zero length");
+        }
+        this.value = new BigInteger(Utils.byteToByte(encoded.require(getLength(), true)));
+    }
+
+    /**
+     * EFFECTS: Produce the big-endian two's complement encoding of the value, in the shortest possible way (i.e., no
+     * leading 0x0 bytes, and no leading 0xFF bytes if negative). Notes, if a positive number is desired (or mandated
+     * like {@link TbsCertificate#getSerialNumber()}, append 0x0 to the MSB manually. This method always results in a
+     * signed integer. For simplicity, the first 0x0 is always removed except when the number itself is 0, and others
+     * are kept.
+     */
+    @Override
+    public Byte[] encodeValueDER() {
+        Byte[] bytes = Utils.byteToByte(value.toByteArray());
+        if (bytes.length == 1) {
+            return bytes;
+        }
+        if (bytes[0] == 0x0) {
+            return Arrays.stream(bytes)
+                    .skip(1)
+                    .toArray(Byte[]::new);
+        }
+        return bytes;
+    }
+
+    /**
+     * EFFECTS: Get the value in long.
+     *   Throws {@link ArithmeticException} if the value is too large for long.
+     */
+    public long getLong() throws ArithmeticException {
+        return value.longValueExact();
+    }
+
+    public BigInteger getValue() {
+        return value;
+    }
+}
-- 
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