1 files changed, 78 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/crypto/gmss/util/GMSSRandom.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/crypto/gmss/util/GMSSRandom.java
new file mode 100644
index 000000000..367aae0e2
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/pqc/crypto/gmss/util/GMSSRandom.java
@@ -0,0 +1,78 @@
+package org.spongycastle.pqc.crypto.gmss.util;
+
+import org.spongycastle.crypto.Digest;
+
+/**
+ * This class provides a PRNG for GMSS
+ */
+public class GMSSRandom
+{
+    /**
+     * Hash function for the construction of the authentication trees
+     */
+    private Digest messDigestTree;
+
+    /**
+     * Constructor
+     *
+     * @param messDigestTree2
+     */
+    public GMSSRandom(Digest messDigestTree2)
+    {
+
+        this.messDigestTree = messDigestTree2;
+    }
+
+    /**
+     * computes the next seed value, returns a random byte array and sets
+     * outseed to the next value
+     *
+     * @param outseed byte array in which ((1 + SEEDin +RAND) mod 2^n) will be
+     *                stored
+     * @return byte array of H(SEEDin)
+     */
+    public byte[] nextSeed(byte[] outseed)
+    {
+        // RAND <-- H(SEEDin)
+        byte[] rand = new byte[outseed.length];
+        messDigestTree.update(outseed, 0, outseed.length);
+        rand = new byte[messDigestTree.getDigestSize()];
+        messDigestTree.doFinal(rand, 0);
+
+        // SEEDout <-- (1 + SEEDin +RAND) mod 2^n
+        addByteArrays(outseed, rand);
+        addOne(outseed);
+
+        // System.arraycopy(outseed, 0, outseed, 0, outseed.length);
+
+        return rand;
+    }
+
+    private void addByteArrays(byte[] a, byte[] b)
+    {
+
+        byte overflow = 0;
+        int temp;
+
+        for (int i = 0; i < a.length; i++)
+        {
+            temp = (0xFF & a[i]) + (0xFF & b[i]) + overflow;
+            a[i] = (byte)temp;
+            overflow = (byte)(temp >> 8);
+        }
+    }
+
+    private void addOne(byte[] a)
+    {
+
+        byte overflow = 1;
+        int temp;
+
+        for (int i = 0; i < a.length; i++)
+        {
+            temp = (0xFF & a[i]) + overflow;
+            a[i] = (byte)temp;
+            overflow = (byte)(temp >> 8);
+        }
+    }
+}