Add documentation for AEADAlgorithmTags

pg/src/main/java/org/bouncycastle/bcpg/AEADAlgorithmTags.java

@@ -1,8 +1,31 @@
 package org.bouncycastle.bcpg;
 
+/**
+ * AEAD Algorithm IDs.
+ * Crypto-Refresh (OpenPGP) defines IDs 1 through 3, while LibrePGP only defines 1 and 2.
+ * Further, the use of AEAD differs between C-R and LibrePGP.
+ *
+ * @see <a href="https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-13.html#name-aead-algorithms">
+ *     Crypto-Refresh: AEAD Algorithms</a>
+ * @see <a href="https://www.ietf.org/archive/id/draft-koch-librepgp-00.html#name-encryption-modes">
+ *     LibrePGP - Encryption Modes</a>
+ */
 public interface AEADAlgorithmTags
 {
-    int EAX = 1;    // EAX (IV len: 16 octets, Tag len: 16 octets)
-    int OCB = 2;    // OCB (IV len: 15 octets, Tag len: 16 octets)
-    int GCM = 3;    // GCM (IV len: 12 octets, Tag len: 16 octets)
+    /**
+     * EAX with 16-bit nonce/IV and 16-bit auth tag length.
+     */
+    int EAX = 1;
+    /**
+     * OCB with 15-bit nonce/IV and 16-bit auth tag length.
+     * C-R compliant implementations MUST implement OCB.
+     */
+    int OCB = 2;
+    /**
+     * GCM with 12-bit nonce/IV and 16-bit auth tag length.
+     * OpenPGP only.
+     */
+    int GCM = 3;
+
+    // 100 to 110: Experimental algorithms
 }