Add private key spec constructor for hash, update javadocs

Closes #17

Author: zzz

src/net/i2p/crypto/eddsa/EdDSAPrivateKey.java

@@ -96,6 +96,9 @@ public String getFormat() {
      *  This will hopefully be clarified in the next draft.
      *  But sun.security.pkcs.PKCS8Key expects them so we must include them for keytool to work.
      *
+     *  This encodes the seed. It will return null if constructed from
+     *  a spec which was directly constructed from H, in which case seed is null.
+     *
      *  @return 49 bytes for Ed25519, null for other curves
      */
     public byte[] getEncoded() {
@@ -178,22 +181,38 @@ public EdDSAParameterSpec getParams() {
         return edDsaSpec;
     }
 
+    /**
+     *  @return will be null if constructed from a spec which was
+     *          directly constructed from H
+     */
     public byte[] getSeed() {
         return seed;
     }
 
+    /**
+     *  @return the hash of the seed
+     */
     public byte[] getH() {
         return h;
     }
 
+    /**
+     *  @return the private key
+     */
     public byte[] geta() {
         return a;
     }
 
+    /**
+     *  @return the public key
+     */
     public GroupElement getA() {
         return A;
     }
 
+    /**
+     *  @return the public key
+     */
     public byte[] getAbyte() {
         return Abyte;
     }

src/net/i2p/crypto/eddsa/spec/EdDSAParameterSpec.java

@@ -65,6 +65,9 @@ public ScalarOps getScalarOps() {
         return sc;
     }
 
+    /**
+     *  @return the base (generator)
+     */
     public GroupElement getB() {
         return B;
     }

src/net/i2p/crypto/eddsa/spec/EdDSAPrivateKeySpec.java

@@ -60,6 +60,27 @@ public EdDSAPrivateKeySpec(byte[] seed, EdDSAParameterSpec spec) {
         }
     }
 
+    /**
+     *  Initialize directly from the hash.
+     *  getSeed() will return null if this constructor is used.
+     *
+     *  @param h the private key
+     *  @since 0.1.1
+     */
+    public EdDSAPrivateKeySpec(EdDSAParameterSpec spec, byte[] h) {
+	this.seed = null;
+	this.h = h;
+	this.spec = spec;
+	int b = spec.getCurve().getField().getb();
+
+        h[0] &= 248;
+        h[(b/8)-1] &= 63;
+        h[(b/8)-1] |= 64;
+        a = Arrays.copyOfRange(h, 0, b/8);
+
+        A = spec.getB().scalarMultiply(a);
+    }
+
     public EdDSAPrivateKeySpec(byte[] seed, byte[] h, byte[] a, GroupElement A, EdDSAParameterSpec spec) {
         this.seed = seed;
         this.h = h;
@@ -68,18 +89,30 @@ public EdDSAPrivateKeySpec(byte[] seed, byte[] h, byte[] a, GroupElement A, EdDS
         this.spec = spec;        
     }
 
+    /**
+     *  @return will be null if constructed directly from the private key
+     */
     public byte[] getSeed() {
         return seed;
     }
 
+    /**
+     *  @return the hash
+     */
     public byte[] getH() {
         return h;
     }
 
+    /**
+     *  @return the private key
+     */
     public byte[] geta() {
         return a;
     }
 
+    /**
+     *  @return the public key
+     */
     public GroupElement getA() {
         return A;
     }