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package org.bouncycastle.cert.crmf.bc;
import java.security.SecureRandom;
import org.bouncycastle.cert.crmf.EncryptedValuePadder;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.digests.SHA1Digest;
import org.bouncycastle.crypto.generators.MGF1BytesGenerator;
import org.bouncycastle.crypto.params.MGFParameters;
/**
* An encrypted value padder that uses MGF1 as the basis of the padding.
*/
public class BcFixedLengthMGF1Padder
implements EncryptedValuePadder
{
private int length;
private SecureRandom random;
private Digest dig = new SHA1Digest();
/**
* Create a padder to so that padded output will always be at least
* length bytes long.
*
* @param length fixed length for padded output.
*/
public BcFixedLengthMGF1Padder(int length)
{
this(length, null);
}
/**
* Create a padder to so that padded output will always be at least
* length bytes long, using the passed in source of randomness to
* provide the random material for the padder.
*
* @param length fixed length for padded output.
* @param random a source of randomness.
*/
public BcFixedLengthMGF1Padder(int length, SecureRandom random)
{
this.length = length;
this.random = random;
}
public byte[] getPaddedData(byte[] data)
{
byte[] bytes = new byte[length];
byte[] seed = new byte[dig.getDigestSize()];
byte[] mask = new byte[length - dig.getDigestSize()];
if (random == null)
{
random = new SecureRandom();
}
random.nextBytes(seed);
MGF1BytesGenerator maskGen = new MGF1BytesGenerator(dig);
maskGen.init(new MGFParameters(seed));
maskGen.generateBytes(mask, 0, mask.length);
System.arraycopy(seed, 0, bytes, 0, seed.length);
System.arraycopy(data, 0, bytes, seed.length, data.length);
for (int i = seed.length + data.length + 1; i != bytes.length; i++)
{
bytes[i] = (byte)(1 + nextByte(random));
}
for (int i = 0; i != mask.length; i++)
{
bytes[i + seed.length] ^= mask[i];
}
return bytes;
}
public byte[] getUnpaddedData(byte[] paddedData)
{
byte[] seed = new byte[dig.getDigestSize()];
byte[] mask = new byte[length - dig.getDigestSize()];
System.arraycopy(paddedData, 0, seed, 0, seed.length);
MGF1BytesGenerator maskGen = new MGF1BytesGenerator(dig);
maskGen.init(new MGFParameters(seed));
maskGen.generateBytes(mask, 0, mask.length);
for (int i = 0; i != mask.length; i++)
{
paddedData[i + seed.length] ^= mask[i];
}
int end = 0;
for (int i = paddedData.length - 1; i != seed.length; i--)
{
if (paddedData[i] == 0)
{
end = i;
break;
}
}
if (end == 0)
{
throw new IllegalStateException("bad padding in encoding");
}
byte[] data = new byte[end - seed.length];
System.arraycopy(paddedData, seed.length, data, 0, data.length);
return data;
}
private int nextByte(SecureRandom random)
{
int bits, val;
do
{
bits = random.nextInt() & 0x7fffffff;
val = bits % 255;
}
while (bits - val + 254 < 0);
return val;
}
}
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