1 files changed, 82 insertions, 0 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/crypto/prng/drbg/DualECPoints.java b/bcprov/src/main/java/org/bouncycastle/crypto/prng/drbg/DualECPoints.java
new file mode 100644
index 0000000..c3715bc
--- /dev/null
+++ b/bcprov/src/main/java/org/bouncycastle/crypto/prng/drbg/DualECPoints.java
@@ -0,0 +1,82 @@
+package org.bouncycastle.crypto.prng.drbg;
+
+import org.bouncycastle.math.ec.ECPoint;
+
+/**
+ * General class for providing point pairs for use with DualEC DRBG. See NIST SP 800-90A for further details.
+ */
+public class DualECPoints
+{
+    private final ECPoint p;
+    private final ECPoint q;
+    private final int securityStrength;
+    private final int cofactor;
+
+    /**
+     * Base Constructor.
+     * <p>
+     * The cofactor is used to calculate the output block length (maxOutlen) according to
+     * <pre>
+     *     max_outlen = largest multiple of 8 less than ((field size in bits) - (13 + log2(cofactor))
+     * </pre>
+     * </p>
+     * @param securityStrength maximum security strength to be associated with these parameters
+     * @param p the P point.
+     * @param q the Q point.
+     * @param cofactor cofactor associated with the domain parameters for the point generation.
+     */
+    public DualECPoints(int securityStrength, ECPoint p, ECPoint q, int cofactor)
+    {
+        if (!p.getCurve().equals(q.getCurve()))
+        {
+            throw new IllegalArgumentException("points need to be on the same curve");
+        }
+
+        this.securityStrength = securityStrength;
+        this.p = p;
+        this.q = q;
+        this.cofactor = cofactor;
+    }
+
+    public int getSeedLen()
+    {
+        return p.getCurve().getFieldSize();
+    }
+
+    public int getMaxOutlen()
+    {
+        return ((p.getCurve().getFieldSize() - (13 + log2(cofactor))) / 8) * 8;
+    }
+
+    public ECPoint getP()
+    {
+        return p;
+    }
+
+    public ECPoint getQ()
+    {
+        return q;
+    }
+
+    public int getSecurityStrength()
+    {
+        return securityStrength;
+    }
+
+    public int getCofactor()
+    {
+        return cofactor;
+    }
+
+    private static int log2(int value)
+    {
+        int log = 0;
+
+        while ((value >>= 1) != 0)
+        {
+            log++;
+        }
+
+        return log;
+    }
+}