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package org.bouncycastle.crypto.tls;
import java.io.IOException;
import java.io.OutputStream;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.encodings.PKCS1Encoding;
import org.bouncycastle.crypto.engines.RSABlindedEngine;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.params.RSAKeyParameters;
import org.bouncycastle.util.Arrays;
public class TlsRSAUtils
{
public static byte[] generateEncryptedPreMasterSecret(TlsContext context, RSAKeyParameters rsaServerPublicKey,
OutputStream output) throws IOException
{
/*
* Choose a PremasterSecret and send it encrypted to the server
*/
byte[] premasterSecret = new byte[48];
context.getSecureRandom().nextBytes(premasterSecret);
TlsUtils.writeVersion(context.getClientVersion(), premasterSecret, 0);
PKCS1Encoding encoding = new PKCS1Encoding(new RSABlindedEngine());
encoding.init(true, new ParametersWithRandom(rsaServerPublicKey, context.getSecureRandom()));
try
{
byte[] encryptedPreMasterSecret = encoding.processBlock(premasterSecret, 0, premasterSecret.length);
if (TlsUtils.isSSL(context))
{
// TODO Do any SSLv3 servers actually expect the length?
output.write(encryptedPreMasterSecret);
}
else
{
TlsUtils.writeOpaque16(encryptedPreMasterSecret, output);
}
}
catch (InvalidCipherTextException e)
{
/*
* This should never happen, only during decryption.
*/
throw new TlsFatalAlert(AlertDescription.internal_error, e);
}
return premasterSecret;
}
public static byte[] safeDecryptPreMasterSecret(TlsContext context, RSAKeyParameters rsaServerPrivateKey,
byte[] encryptedPreMasterSecret)
{
/*
* RFC 5246 7.4.7.1.
*/
ProtocolVersion clientVersion = context.getClientVersion();
// TODO Provide as configuration option?
boolean versionNumberCheckDisabled = false;
/*
* Generate 48 random bytes we can use as a Pre-Master-Secret, if the
* PKCS1 padding check should fail.
*/
byte[] fallback = new byte[48];
context.getSecureRandom().nextBytes(fallback);
byte[] M = Arrays.clone(fallback);
try
{
PKCS1Encoding encoding = new PKCS1Encoding(new RSABlindedEngine(), fallback);
encoding.init(false,
new ParametersWithRandom(rsaServerPrivateKey, context.getSecureRandom()));
M = encoding.processBlock(encryptedPreMasterSecret, 0, encryptedPreMasterSecret.length);
}
catch (Exception e)
{
/*
* This should never happen since the decryption should never throw an exception
* and return a random value instead.
*
* In any case, a TLS server MUST NOT generate an alert if processing an
* RSA-encrypted premaster secret message fails, or the version number is not as
* expected. Instead, it MUST continue the handshake with a randomly generated
* premaster secret.
*/
}
/*
* If ClientHello.client_version is TLS 1.1 or higher, server implementations MUST
* check the version number [..].
*/
if (versionNumberCheckDisabled && clientVersion.isEqualOrEarlierVersionOf(ProtocolVersion.TLSv10))
{
/*
* If the version number is TLS 1.0 or earlier, server
* implementations SHOULD check the version number, but MAY have a
* configuration option to disable the check.
*
* So there is nothing to do here.
*/
}
else
{
/*
* OK, we need to compare the version number in the decrypted Pre-Master-Secret with the
* clientVersion received during the handshake. If they don't match, we replace the
* decrypted Pre-Master-Secret with a random one.
*/
int correct = (clientVersion.getMajorVersion() ^ (M[0] & 0xff))
| (clientVersion.getMinorVersion() ^ (M[1] & 0xff));
correct |= correct >> 1;
correct |= correct >> 2;
correct |= correct >> 4;
int mask = ~((correct & 1) - 1);
/*
* mask will be all bits set to 0xff if the version number differed.
*/
for (int i = 0; i < 48; i++)
{
M[i] = (byte)((M[i] & (~mask)) | (fallback[i] & mask));
}
}
return M;
}
}
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