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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 and up.
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package org.bouncycastle.crypto.digests;
import org.bouncycastle.util.Arrays;
/**
* Customizable SHAKE function.
*/
public class CSHAKEDigest
extends SHAKEDigest
{
private static final byte[] padding = new byte[100];
private final byte[] diff;
/**
* Base constructor.
*
* @param bitLength bit length of the underlying SHAKE function, 128 or 256.
* @param N the function name string, note this is reserved for use by NIST. Avoid using it if not required.
* @param S the customization string - available for local use.
*/
public CSHAKEDigest(int bitLength, byte[] N, byte[] S)
{
super(bitLength);
if ((N == null || N.length == 0) && (S == null || S.length == 0))
{
diff = null;
}
else
{
diff = Arrays.concatenate(XofUtils.leftEncode(rate / 8), encodeString(N), encodeString(S));
diffPadAndAbsorb();
}
}
CSHAKEDigest(CSHAKEDigest source)
{
super(source);
this.diff = Arrays.clone(source.diff);
}
// bytepad in SP 800-185
private void diffPadAndAbsorb()
{
int blockSize = rate / 8;
absorb(diff, 0, diff.length);
int delta = diff.length % blockSize;
// only add padding if needed
if (delta != 0)
{
int required = blockSize - delta;
while (required > padding.length)
{
absorb(padding, 0, padding.length);
required -= padding.length;
}
absorb(padding, 0, required);
}
}
private byte[] encodeString(byte[] str)
{
if (str == null || str.length == 0)
{
return XofUtils.leftEncode(0);
}
return Arrays.concatenate(XofUtils.leftEncode(str.length * 8L), str);
}
public String getAlgorithmName()
{
return "CSHAKE" + fixedOutputLength;
}
public int doOutput(byte[] out, int outOff, int outLen)
{
if (diff != null)
{
if (!squeezing)
{
absorbBits(0x00, 2);
}
squeeze(out, outOff, ((long)outLen) * 8);
return outLen;
}
else
{
return super.doOutput(out, outOff, outLen);
}
}
public void reset()
{
super.reset();
if (diff != null)
{
diffPadAndAbsorb();
}
}
}
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