1 files changed, 74 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/kdf/ECDHKEKGenerator.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/kdf/ECDHKEKGenerator.java
new file mode 100644
index 000000000..d427f9895
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/kdf/ECDHKEKGenerator.java
@@ -0,0 +1,74 @@
+package org.spongycastle.crypto.agreement.kdf;
+
+import java.io.IOException;
+
+import org.spongycastle.asn1.ASN1EncodableVector;
+import org.spongycastle.asn1.ASN1Encoding;
+import org.spongycastle.asn1.ASN1ObjectIdentifier;
+import org.spongycastle.asn1.DERNull;
+import org.spongycastle.asn1.DEROctetString;
+import org.spongycastle.asn1.DERSequence;
+import org.spongycastle.asn1.DERTaggedObject;
+import org.spongycastle.asn1.x509.AlgorithmIdentifier;
+import org.spongycastle.crypto.DataLengthException;
+import org.spongycastle.crypto.DerivationParameters;
+import org.spongycastle.crypto.Digest;
+import org.spongycastle.crypto.DigestDerivationFunction;
+import org.spongycastle.crypto.generators.KDF2BytesGenerator;
+import org.spongycastle.crypto.params.KDFParameters;
+import org.spongycastle.crypto.util.Pack;
+
+/**
+ * X9.63 based key derivation function for ECDH CMS.
+ */
+public class ECDHKEKGenerator
+    implements DigestDerivationFunction
+{
+    private DigestDerivationFunction kdf;
+
+    private ASN1ObjectIdentifier algorithm;
+    private int                 keySize;
+    private byte[]              z;
+
+    public ECDHKEKGenerator(
+        Digest digest)
+    {
+        this.kdf = new KDF2BytesGenerator(digest);
+    }
+
+    public void init(DerivationParameters param)
+    {
+        DHKDFParameters params = (DHKDFParameters)param;
+
+        this.algorithm = params.getAlgorithm();
+        this.keySize = params.getKeySize();
+        this.z = params.getZ();
+    }
+
+    public Digest getDigest()
+    {
+        return kdf.getDigest();
+    }
+
+    public int generateBytes(byte[] out, int outOff, int len)
+        throws DataLengthException, IllegalArgumentException
+    {
+        // TODO Create an ASN.1 class for this (RFC3278)
+        // ECC-CMS-SharedInfo
+        ASN1EncodableVector v = new ASN1EncodableVector();
+
+        v.add(new AlgorithmIdentifier(algorithm, DERNull.INSTANCE));
+        v.add(new DERTaggedObject(true, 2, new DEROctetString(Pack.intToBigEndian(keySize))));
+
+        try
+        {
+            kdf.init(new KDFParameters(z, new DERSequence(v).getEncoded(ASN1Encoding.DER)));
+        }
+        catch (IOException e)
+        {
+            throw new IllegalArgumentException("unable to initialise kdf: " + e.getMessage());
+        }
+
+        return kdf.generateBytes(out, outOff, len);
+    }
+}