1 files changed, 114 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/MGF1BytesGenerator.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/MGF1BytesGenerator.java
new file mode 100644
index 000000000..03cb7ba50
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/MGF1BytesGenerator.java
@@ -0,0 +1,114 @@
+package org.spongycastle.crypto.generators;
+
+import org.spongycastle.crypto.DataLengthException;
+import org.spongycastle.crypto.DerivationFunction;
+import org.spongycastle.crypto.DerivationParameters;
+import org.spongycastle.crypto.Digest;
+import org.spongycastle.crypto.params.MGFParameters;
+
+/**
+ * Generator for MGF1 as defined in PKCS 1v2
+ */
+public class MGF1BytesGenerator
+    implements DerivationFunction
+{
+    private Digest  digest;
+    private byte[]  seed;
+    private int     hLen;
+
+    /**
+     * @param digest the digest to be used as the source of generated bytes
+     */
+    public MGF1BytesGenerator(
+        Digest  digest)
+    {
+        this.digest = digest;
+        this.hLen = digest.getDigestSize();
+    }
+
+    public void init(
+        DerivationParameters    param)
+    {
+        if (!(param instanceof MGFParameters))
+        {
+            throw new IllegalArgumentException("MGF parameters required for MGF1Generator");
+        }
+
+        MGFParameters   p = (MGFParameters)param;
+
+        seed = p.getSeed();
+    }
+
+    /**
+     * return the underlying digest.
+     */
+    public Digest getDigest()
+    {
+        return digest;
+    }
+
+    /**
+     * int to octet string.
+     */
+    private void ItoOSP(
+        int     i,
+        byte[]  sp)
+    {
+        sp[0] = (byte)(i >>> 24);
+        sp[1] = (byte)(i >>> 16);
+        sp[2] = (byte)(i >>> 8);
+        sp[3] = (byte)(i >>> 0);
+    }
+
+    /**
+     * fill len bytes of the output buffer with bytes generated from
+     * the derivation function.
+     *
+     * @throws DataLengthException if the out buffer is too small.
+     */
+    public int generateBytes(
+        byte[]  out,
+        int     outOff,
+        int     len)
+        throws DataLengthException, IllegalArgumentException
+    {
+        if ((out.length - len) < outOff)
+        {
+            throw new DataLengthException("output buffer too small");
+        }
+        
+        byte[]  hashBuf = new byte[hLen];
+        byte[]  C = new byte[4];
+        int     counter = 0;
+
+        digest.reset();
+
+        if (len > hLen)
+        {
+            do
+            {
+                ItoOSP(counter, C);
+    
+                digest.update(seed, 0, seed.length);
+                digest.update(C, 0, C.length);
+                digest.doFinal(hashBuf, 0);
+    
+                System.arraycopy(hashBuf, 0, out, outOff + counter * hLen, hLen);
+            }
+            while (++counter < (len / hLen));
+        }
+
+        if ((counter * hLen) < len)
+        {
+            ItoOSP(counter, C);
+
+            digest.update(seed, 0, seed.length);
+            digest.update(C, 0, C.length);
+            digest.doFinal(hashBuf, 0);
+
+            System.arraycopy(hashBuf, 0, out, outOff + counter * hLen, len - (counter * hLen));
+        }
+
+        return len;
+    }
+}