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Spongy Castle is a package-rename (org.bouncycastle.* to org.spongycastle.*) of Bouncy Castle
intended for the Android platform. Android unfortunately ships with a stripped-down version of
Bouncy Castle, which prevents easy upgrades - Spongy Castle overcomes this and provides a full,
up-to-date version of the Bouncy Castle cryptographic libs.
package org.spongycastle.crypto.engines;
import org.spongycastle.util.Pack;
/**
* Implementation of Daniel J. Bernstein's ChaCha stream cipher.
*/
public class ChaChaEngine extends Salsa20Engine
{
/**
* Creates a 20 rounds ChaCha engine.
*/
public ChaChaEngine()
{
super();
}
/**
* Creates a ChaCha engine with a specific number of rounds.
* @param rounds the number of rounds (must be an even number).
*/
public ChaChaEngine(int rounds)
{
super(rounds);
}
public String getAlgorithmName()
{
return "ChaCha" + rounds;
}
protected void advanceCounter(long diff)
{
int hi = (int)(diff >>> 32);
int lo = (int)diff;
if (hi > 0)
{
engineState[13] += hi;
}
int oldState = engineState[12];
engineState[12] += lo;
if (oldState != 0 && engineState[12] < oldState)
{
engineState[13]++;
}
}
protected void advanceCounter()
{
if (++engineState[12] == 0)
{
++engineState[13];
}
}
protected void retreatCounter(long diff)
{
int hi = (int)(diff >>> 32);
int lo = (int)diff;
if (hi != 0)
{
if ((engineState[13] & 0xffffffffL) >= (hi & 0xffffffffL))
{
engineState[13] -= hi;
}
else
{
throw new IllegalStateException("attempt to reduce counter past zero.");
}
}
if ((engineState[12] & 0xffffffffL) >= (lo & 0xffffffffL))
{
engineState[12] -= lo;
}
else
{
if (engineState[13] != 0)
{
--engineState[13];
engineState[12] -= lo;
}
else
{
throw new IllegalStateException("attempt to reduce counter past zero.");
}
}
}
protected void retreatCounter()
{
if (engineState[12] == 0 && engineState[13] == 0)
{
throw new IllegalStateException("attempt to reduce counter past zero.");
}
if (--engineState[12] == -1)
{
--engineState[13];
}
}
protected long getCounter()
{
return ((long)engineState[13] << 32) | (engineState[12] & 0xffffffffL);
}
protected void resetCounter()
{
engineState[12] = engineState[13] = 0;
}
protected void setKey(byte[] keyBytes, byte[] ivBytes)
{
if (keyBytes != null)
{
if ((keyBytes.length != 16) && (keyBytes.length != 32))
{
throw new IllegalArgumentException(getAlgorithmName() + " requires 128 bit or 256 bit key");
}
// Key
engineState[4] = Pack.littleEndianToInt(keyBytes, 0);
engineState[5] = Pack.littleEndianToInt(keyBytes, 4);
engineState[6] = Pack.littleEndianToInt(keyBytes, 8);
engineState[7] = Pack.littleEndianToInt(keyBytes, 12);
byte[] constants;
int offset;
if (keyBytes.length == 32)
{
constants = sigma;
offset = 16;
}
else
{
constants = tau;
offset = 0;
}
engineState[8] = Pack.littleEndianToInt(keyBytes, offset);
engineState[9] = Pack.littleEndianToInt(keyBytes, offset + 4);
engineState[10] = Pack.littleEndianToInt(keyBytes, offset + 8);
engineState[11] = Pack.littleEndianToInt(keyBytes, offset + 12);
engineState[0] = Pack.littleEndianToInt(constants, 0);
engineState[1] = Pack.littleEndianToInt(constants, 4);
engineState[2] = Pack.littleEndianToInt(constants, 8);
engineState[3] = Pack.littleEndianToInt(constants, 12);
}
// IV
engineState[14] = Pack.littleEndianToInt(ivBytes, 0);
engineState[15] = Pack.littleEndianToInt(ivBytes, 4);
}
protected void generateKeyStream(byte[] output)
{
chachaCore(rounds, engineState, x);
Pack.intToLittleEndian(x, output, 0);
}
/**
* ChacCha function
*
* @param input input data
*/
public static void chachaCore(int rounds, int[] input, int[] x)
{
if (input.length != 16)
{
throw new IllegalArgumentException();
}
if (x.length != 16)
{
throw new IllegalArgumentException();
}
if (rounds % 2 != 0)
{
throw new IllegalArgumentException("Number of rounds must be even");
}
int x00 = input[ 0];
int x01 = input[ 1];
int x02 = input[ 2];
int x03 = input[ 3];
int x04 = input[ 4];
int x05 = input[ 5];
int x06 = input[ 6];
int x07 = input[ 7];
int x08 = input[ 8];
int x09 = input[ 9];
int x10 = input[10];
int x11 = input[11];
int x12 = input[12];
int x13 = input[13];
int x14 = input[14];
int x15 = input[15];
for (int i = rounds; i > 0; i -= 2)
{
x00 += x04; x12 = rotl(x12 ^ x00, 16);
x08 += x12; x04 = rotl(x04 ^ x08, 12);
x00 += x04; x12 = rotl(x12 ^ x00, 8);
x08 += x12; x04 = rotl(x04 ^ x08, 7);
x01 += x05; x13 = rotl(x13 ^ x01, 16);
x09 += x13; x05 = rotl(x05 ^ x09, 12);
x01 += x05; x13 = rotl(x13 ^ x01, 8);
x09 += x13; x05 = rotl(x05 ^ x09, 7);
x02 += x06; x14 = rotl(x14 ^ x02, 16);
x10 += x14; x06 = rotl(x06 ^ x10, 12);
x02 += x06; x14 = rotl(x14 ^ x02, 8);
x10 += x14; x06 = rotl(x06 ^ x10, 7);
x03 += x07; x15 = rotl(x15 ^ x03, 16);
x11 += x15; x07 = rotl(x07 ^ x11, 12);
x03 += x07; x15 = rotl(x15 ^ x03, 8);
x11 += x15; x07 = rotl(x07 ^ x11, 7);
x00 += x05; x15 = rotl(x15 ^ x00, 16);
x10 += x15; x05 = rotl(x05 ^ x10, 12);
x00 += x05; x15 = rotl(x15 ^ x00, 8);
x10 += x15; x05 = rotl(x05 ^ x10, 7);
x01 += x06; x12 = rotl(x12 ^ x01, 16);
x11 += x12; x06 = rotl(x06 ^ x11, 12);
x01 += x06; x12 = rotl(x12 ^ x01, 8);
x11 += x12; x06 = rotl(x06 ^ x11, 7);
x02 += x07; x13 = rotl(x13 ^ x02, 16);
x08 += x13; x07 = rotl(x07 ^ x08, 12);
x02 += x07; x13 = rotl(x13 ^ x02, 8);
x08 += x13; x07 = rotl(x07 ^ x08, 7);
x03 += x04; x14 = rotl(x14 ^ x03, 16);
x09 += x14; x04 = rotl(x04 ^ x09, 12);
x03 += x04; x14 = rotl(x14 ^ x03, 8);
x09 += x14; x04 = rotl(x04 ^ x09, 7);
}
x[ 0] = x00 + input[ 0];
x[ 1] = x01 + input[ 1];
x[ 2] = x02 + input[ 2];
x[ 3] = x03 + input[ 3];
x[ 4] = x04 + input[ 4];
x[ 5] = x05 + input[ 5];
x[ 6] = x06 + input[ 6];
x[ 7] = x07 + input[ 7];
x[ 8] = x08 + input[ 8];
x[ 9] = x09 + input[ 9];
x[10] = x10 + input[10];
x[11] = x11 + input[11];
x[12] = x12 + input[12];
x[13] = x13 + input[13];
x[14] = x14 + input[14];
x[15] = x15 + input[15];
}
}
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