Add documentation to individual PK algorithm tags

Author: vanitasvitae

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

@@ -12,29 +12,79 @@
  */
 public interface PublicKeyAlgorithmTags 
 {
+    /**
+     * RSA encryption/signing algorithm.
+     */
     int RSA_GENERAL = 1;       // RSA (Encrypt or Sign)
+    /**
+     * Deprecated tag for encrypt-only RSA.
+     * MUST NOT be generated.
+     */
     int RSA_ENCRYPT = 2;       // RSA Encrypt-Only
+    /**
+     * Deprecated tag for sign-only RSA.
+     * MUST NOT be generated.
+     */
     int RSA_SIGN = 3;          // RSA Sign-Only
+    /**
+     * Encrypt-only ElGamal.
+     */
     int ELGAMAL_ENCRYPT = 16;  // Elgamal (Encrypt-Only), see [ELGAMAL]
+    /**
+     * DSA.
+     */
     int DSA = 17;              // DSA (Digital Signature Standard)
     /**
-     * @deprecated use ECDH
+     * Deprecated tag for ECDH.
+     * @deprecated use {@link #ECDH} instead.
+     */
+    int EC = 18;               // Misnamed constant
+    /**
+     * Elliptic curve Diffie-Hellman.
+     */
+    int ECDH = 18;             // Elliptic Curve Diffie-Hellman
+    /**
+     * Elliptic curve digital signing algorithm.
+     */
+    int ECDSA = 19;            // Elliptic Curve Digital Signing Algorithm
+    /**
+     * Reserved tag for sign+encrypt ElGamal.
+     * MUST NOT be generated.
+     * An implementation MUST NOT generate ElGamal signatures.
+     */
+    int ELGAMAL_GENERAL = 20;  // Reserved Elgamal (Encrypt or Sign)
+    /**
+     * Reserved tag for IETF-style S/MIME Diffie-Hellman.
      */
-    int EC = 18;               // Reserved for Elliptic Curve
-    int ECDH = 18;             // Reserved for Elliptic Curve (actual algorithm name)
-    int ECDSA = 19;            // Reserved for ECDSA
-    int ELGAMAL_GENERAL = 20;  // Elgamal (Encrypt or Sign)
     int DIFFIE_HELLMAN = 21;   // Reserved for Diffie-Hellman (X9.42, as defined for IETF-S/MIME)
     /**
-     * @deprecated use Ed25519 or Ed448
+     * Misnamed tag for legacy EdDSA.
+     * @deprecated use {@link #EDDSA_LEGACY} instead.
+     */
+    int EDDSA = 22;            // EdDSA - (internet draft, but appearing in use); misnamed constant
+    /**
+     * Legacy EdDSA (curve identified by OID).
+     * MUST NOT be used with v6 keys (use {@link #Ed25519}, {@link #Ed448} instead).
      */
-    int EDDSA = 22;            // EdDSA - (internet draft, but appearing in use)
     int EDDSA_LEGACY = 22;     // new name for old EDDSA tag.
-    
-    int X25519 = 25;
-    int X448 = 26;
-    int Ed25519 = 27;
-    int Ed448 = 28;
+    /**
+     * X25519 encryption algorithm.
+     * C-R compliant implementations MUST implement support for this.
+     */
+    int X25519 = 25;           // X25519
+    /**
+     * X448 encryption algorithm.
+     */
+    int X448 = 26;             // X448
+    /**
+     * Ed25519 signing algorithm.
+     * C-R compliant implementations MUST implement support for this.
+     */
+    int Ed25519 = 27;          // new style Ed25519
+    /**
+     * Ed448 signing algorithm.
+     */
+    int Ed448 = 28;            // new style Ed448
 
     int EXPERIMENTAL_1 = 100;
     int EXPERIMENTAL_2 = 101;