java/6 : sun/security/ssl/CipherBox.java

CipherBox
https://openjdk.java.net/
GPLv2 + Classpath Exception
/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */


package sun.security.ssl;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.util.Hashtable;

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.spec.IvParameterSpec;

import java.nio.*;

import sun.security.ssl.CipherSuite.*;
import static sun.security.ssl.CipherSuite.*;

import sun.misc.HexDumpEncoder;


This class handles bulk data enciphering/deciphering for each SSLv3
message.  This provides data confidentiality.  Stream ciphers (such
as RC4) don't need to do padding; block ciphers (e.g. DES) need it.
Individual instances are obtained by calling the static method
newCipherBox(), which should only be invoked by BulkCipher.newCipher().
In RFC 2246, with bock ciphers in CBC mode, the Initialization
Vector (IV) for the first record is generated with the other keys
and secrets when the security parameters are set.  The IV for
subsequent records is the last ciphertext block from the previous
record.
In RFC 4346, the implicit Initialization Vector (IV) is replaced
with an explicit IV to protect against CBC attacks.  RFC 4346
recommends two algorithms used to generated the per-record IV.
The implementation uses the algorithm (2)(b), as described at
section 6.2.3.2 of RFC 4346.
The usage of IV in CBC block cipher can be illustrated in
the following diagrams.
  (random)
       R         P1                    IV        C1
       |          |                     |         |
 SIV---+    |-----+    |-...            |-----    |------
       |    |     |    |                |    |    |     |
    +----+  |  +----+  |             +----+  |  +----+  |
    | Ek |  |  + Ek +  |             | Dk |  |  | Dk |  |
    +----+  |  +----+  |             +----+  |  +----+  |
       |    |     |    |                |    |    |     |
       |----|     |----|           SIV--+    |----|     |-...
       |          |                     |       |
      IV         C1                     R      P1
                                    (discard)
      CBC Encryption                    CBC Decryption
NOTE that any ciphering involved in key exchange (e.g. with RSA) is
handled separately.
Author: David Brownell, Andreas Sterbenz/**
 * This class handles bulk data enciphering/deciphering for each SSLv3
 * message.  This provides data confidentiality.  Stream ciphers (such
 * as RC4) don't need to do padding; block ciphers (e.g. DES) need it.
 *
 * Individual instances are obtained by calling the static method
 * newCipherBox(), which should only be invoked by BulkCipher.newCipher().
 *
 * In RFC 2246, with bock ciphers in CBC mode, the Initialization
 * Vector (IV) for the first record is generated with the other keys
 * and secrets when the security parameters are set.  The IV for
 * subsequent records is the last ciphertext block from the previous
 * record.
 *
 * In RFC 4346, the implicit Initialization Vector (IV) is replaced
 * with an explicit IV to protect against CBC attacks.  RFC 4346
 * recommends two algorithms used to generated the per-record IV.
 * The implementation uses the algorithm (2)(b), as described at
 * section 6.2.3.2 of RFC 4346.
 *
 * The usage of IV in CBC block cipher can be illustrated in
 * the following diagrams.
 *
 *   (random)
 *        R         P1                    IV        C1
 *        |          |                     |         |
 *  SIV---+    |-----+    |-...            |-----    |------
 *        |    |     |    |                |    |    |     |
 *     +----+  |  +----+  |             +----+  |  +----+  |
 *     | Ek |  |  + Ek +  |             | Dk |  |  | Dk |  |
 *     +----+  |  +----+  |             +----+  |  +----+  |
 *        |    |     |    |                |    |    |     |
 *        |----|     |----|           SIV--+    |----|     |-...
 *        |          |                     |       |
 *       IV         C1                     R      P1
 *                                     (discard)
 *
 *       CBC Encryption                    CBC Decryption
 *
 * NOTE that any ciphering involved in key exchange (e.g. with RSA) is
 * handled separately.
 *
 * @author David Brownell
 * @author Andreas Sterbenz
 */
final class CipherBox {

    // A CipherBox that implements the identity operation
    final static CipherBox NULL = new CipherBox();

    /* Class and subclass dynamic debugging support */
    private static final Debug debug = Debug.getInstance("ssl");

    // the protocol version this cipher conforms to
    private final ProtocolVersion protocolVersion;

    // cipher object
    private final Cipher cipher;

    Cipher blocksize, 0 for stream ciphers
/**
     * Cipher blocksize, 0 for stream ciphers
     */
    private int blockSize;

    Is the cipher of CBC mode?
/**
     * Is the cipher of CBC mode?
     */
     private final boolean isCBCMode;

    secure random
/**
     * secure random
     */
    private SecureRandom random;

    Fixed masks of various block size, as the initial decryption IVs
for TLS 1.1 or later.
For performance, we do not use random IVs. As the initial decryption
IVs will be discarded by TLS decryption processes, so the fixed masks
do not hurt cryptographic strength.
/**
     * Fixed masks of various block size, as the initial decryption IVs
     * for TLS 1.1 or later.
     *
     * For performance, we do not use random IVs. As the initial decryption
     * IVs will be discarded by TLS decryption processes, so the fixed masks
     * do not hurt cryptographic strength.
     */
    private static Hashtable<Integer, IvParameterSpec> masks;

    NULL cipherbox. Identity operation, no encryption.
/**
     * NULL cipherbox. Identity operation, no encryption.
     */
    private CipherBox() {
        this.protocolVersion = ProtocolVersion.DEFAULT;
        this.cipher = null;
        this.isCBCMode = false;
    }

    Construct a new CipherBox using the cipher transformation.
Throws: NoSuchAlgorithmException – if no appropriate JCE Cipher
implementation could be found./**
     * Construct a new CipherBox using the cipher transformation.
     *
     * @exception NoSuchAlgorithmException if no appropriate JCE Cipher
     * implementation could be found.
     */
    private CipherBox(ProtocolVersion protocolVersion, BulkCipher bulkCipher,
            SecretKey key, IvParameterSpec iv, SecureRandom random,
            boolean encrypt) throws NoSuchAlgorithmException {
        try {
            this.protocolVersion = protocolVersion;
            this.cipher = JsseJce.getCipher(bulkCipher.transformation);
            int mode = encrypt ? Cipher.ENCRYPT_MODE : Cipher.DECRYPT_MODE;
            this.isCBCMode = bulkCipher.isCBCMode;

            if (random == null) {
                random = JsseJce.getSecureRandom();
            }
            this.random = random;

            /*
             * RFC 4346 recommends two algorithms used to generated the
             * per-record IV. The implementation uses the algorithm (2)(b),
             * as described at section 6.2.3.2 of RFC 4346.
             *
             * As we don't care about the initial IV value for TLS 1.1 or
             * later, so if the "iv" parameter is null, we use the default
             * value generated by Cipher.init() for encryption, and a fixed
             * mask for decryption.
             */
            if (iv == null && bulkCipher.ivSize != 0 &&
                    mode == Cipher.DECRYPT_MODE &&
                    protocolVersion.v >= ProtocolVersion.TLS11.v) {
                iv = getFixedMask(bulkCipher.ivSize);
            }

            cipher.init(mode, key, iv, random);

            // Do not call getBlockSize until after init()
            // otherwise we would disrupt JCE delayed provider selection
            blockSize = cipher.getBlockSize();
            // some providers implement getBlockSize() incorrectly
            if (blockSize == 1) {
                blockSize = 0;
            }
        } catch (NoSuchAlgorithmException e) {
            throw e;
        } catch (Exception e) {
            throw new NoSuchAlgorithmException
                    ("Could not create cipher " + bulkCipher, e);
        } catch (ExceptionInInitializerError e) {
            throw new NoSuchAlgorithmException
                    ("Could not create cipher " + bulkCipher, e);
        }
    }

    /*
     * Factory method to obtain a new CipherBox object.
     */
    static CipherBox newCipherBox(ProtocolVersion version, BulkCipher cipher,
            SecretKey key, IvParameterSpec iv, SecureRandom random,
            boolean encrypt) throws NoSuchAlgorithmException {
        if (cipher.allowed == false) {
            throw new NoSuchAlgorithmException("Unsupported cipher " + cipher);
        }

        if (cipher == B_NULL) {
            return NULL;
        } else {
            return new CipherBox(version, cipher, key, iv, random, encrypt);
        }
    }

    /*
     * Get a fixed mask, as the initial decryption IVs for TLS 1.1 or later.
     */
    private static IvParameterSpec getFixedMask(int ivSize) {
        if (masks == null) {
            masks = new Hashtable<Integer, IvParameterSpec>(5);
        }

        IvParameterSpec iv = masks.get(ivSize);
        if (iv == null) {
            iv = new IvParameterSpec(new byte[ivSize]);
            masks.put(ivSize, iv);
        }

        return iv;
    }

    /*
     * Encrypts a block of data, returning the size of the
     * resulting block.
     */
    int encrypt(byte[] buf, int offset, int len) {
        if (cipher == null) {
            return len;
        }

        try {
            if (blockSize != 0) {
                // TLSv1.1 needs a IV block
                if (protocolVersion.v >= ProtocolVersion.TLS11.v) {
                    // generate a random number
                    byte[] prefix = new byte[blockSize];
                    random.nextBytes(prefix);

                    // move forward the plaintext
                    System.arraycopy(buf, offset,
                                     buf, offset + prefix.length, len);

                    // prefix the plaintext
                    System.arraycopy(prefix, 0,
                                     buf, offset, prefix.length);

                    len += prefix.length;
                }

                len = addPadding(buf, offset, len, blockSize);
            }
            if (debug != null && Debug.isOn("plaintext")) {
                try {
                    HexDumpEncoder hd = new HexDumpEncoder();

                    System.out.println(
                        "Padded plaintext before ENCRYPTION:  len = "
                        + len);
                    hd.encodeBuffer(
                        new ByteArrayInputStream(buf, offset, len),
                        System.out);
                } catch (IOException e) { }
            }
            int newLen = cipher.update(buf, offset, len, buf, offset);
            if (newLen != len) {
                // catch BouncyCastle buffering error
                throw new RuntimeException("Cipher buffering error " +
                    "in JCE provider " + cipher.getProvider().getName());
            }
            return newLen;
        } catch (ShortBufferException e) {
            throw new ArrayIndexOutOfBoundsException(e.toString());
        }
    }

    /*
     * Encrypts a ByteBuffer block of data, returning the size of the
     * resulting block.
     *
     * The byte buffers position and limit initially define the amount
     * to encrypt.  On return, the position and limit are
     * set to last position padded/encrypted.  The limit may have changed
     * because of the added padding bytes.
     */
    int encrypt(ByteBuffer bb) {

        int len = bb.remaining();

        if (cipher == null) {
            bb.position(bb.limit());
            return len;
        }

        try {
            int pos = bb.position();

            if (blockSize != 0) {
                // TLSv1.1 needs a IV block
                if (protocolVersion.v >= ProtocolVersion.TLS11.v) {
                    // generate a random number
                    byte[] prefix = new byte[blockSize];
                    random.nextBytes(prefix);

                    // move forward the plaintext
                    byte[] buf = null;
                    int limit = bb.limit();
                    if (bb.hasArray()) {
                        int arrayOffset = bb.arrayOffset();
                        buf = bb.array();
                        System.arraycopy(buf, arrayOffset + pos,
                            buf, arrayOffset + pos + prefix.length,
                            limit - pos);
                        bb.limit(limit + prefix.length);
                    } else {
                        buf = new byte[limit - pos];
                        bb.get(buf, 0, limit - pos);
                        bb.position(pos + prefix.length);
                        bb.limit(limit + prefix.length);
                        bb.put(buf);
                    }
                    bb.position(pos);

                    // prefix the plaintext
                    bb.put(prefix);
                    bb.position(pos);
                }

                // addPadding adjusts pos/limit
                len = addPadding(bb, blockSize);
                bb.position(pos);
            }
            if (debug != null && Debug.isOn("plaintext")) {
                try {
                    HexDumpEncoder hd = new HexDumpEncoder();

                    System.out.println(
                        "Padded plaintext before ENCRYPTION:  len = "
                        + len);
                    hd.encodeBuffer(bb, System.out);

                } catch (IOException e) { }
                /*
                 * reset back to beginning
                 */
                bb.position(pos);
            }

            /*
             * Encrypt "in-place".  This does not add its own padding.
             */
            ByteBuffer dup = bb.duplicate();
            int newLen = cipher.update(dup, bb);

            if (bb.position() != dup.position()) {
                throw new RuntimeException("bytebuffer padding error");
            }

            if (newLen != len) {
                // catch BouncyCastle buffering error
                throw new RuntimeException("Cipher buffering error " +
                    "in JCE provider " + cipher.getProvider().getName());
            }
            return newLen;
        } catch (ShortBufferException e) {
            RuntimeException exc = new RuntimeException(e.toString());
            exc.initCause(e);
            throw exc;
        }
    }


    /*
     * Decrypts a block of data, returning the size of the
     * resulting block if padding was required.
     *
     * For SSLv3 and TLSv1.0, with block ciphers in CBC mode the
     * Initialization Vector (IV) for the first record is generated by
     * the handshake protocol, the IV for subsequent records is the
     * last ciphertext block from the previous record.
     *
     * From TLSv1.1, the implicit IV is replaced with an explicit IV to
     * protect against CBC attacks.
     *
     * Differentiating between bad_record_mac and decryption_failed alerts
     * may permit certain attacks against CBC mode. It is preferable to
     * uniformly use the bad_record_mac alert to hide the specific type of
     * the error.
     */
    int decrypt(byte[] buf, int offset, int len,
            int tagLen) throws BadPaddingException {
        if (cipher == null) {
            return len;
        }

        try {
            int newLen = cipher.update(buf, offset, len, buf, offset);
            if (newLen != len) {
                // catch BouncyCastle buffering error
                throw new RuntimeException("Cipher buffering error " +
                    "in JCE provider " + cipher.getProvider().getName());
            }
            if (debug != null && Debug.isOn("plaintext")) {
                try {
                    HexDumpEncoder hd = new HexDumpEncoder();

                    System.out.println(
                        "Padded plaintext after DECRYPTION:  len = "
                        + newLen);
                    hd.encodeBuffer(
                        new ByteArrayInputStream(buf, offset, newLen),
                        System.out);
                } catch (IOException e) { }
            }
            if (blockSize != 0) {
                newLen = removePadding(
                    buf, offset, newLen, tagLen, blockSize, protocolVersion); 

                if (protocolVersion.v >= ProtocolVersion.TLS11.v) {
                    if (newLen < blockSize) {
                        throw new BadPaddingException("invalid explicit IV");
                    }

                    // discards the first cipher block, the IV component.
                    System.arraycopy(buf, offset + blockSize,
                                     buf, offset, newLen - blockSize);

                    newLen -= blockSize;
                }
            }
            return newLen;
        } catch (ShortBufferException e) {
            throw new ArrayIndexOutOfBoundsException(e.toString());
        }
    }


    /*
     * Decrypts a block of data, returning the size of the
     * resulting block if padding was required.  position and limit
     * point to the end of the decrypted/depadded data.  The initial
     * limit and new limit may be different, given we may
     * have stripped off some padding bytes.
     *
     *  @see decrypt(byte[], int, int)
     */
    int decrypt(ByteBuffer bb, int tagLen) throws BadPaddingException {

        int len = bb.remaining();

        if (cipher == null) {
            bb.position(bb.limit());
            return len;
        }

        try {
            /*
             * Decrypt "in-place".
             */
            int pos = bb.position();
            ByteBuffer dup = bb.duplicate();
            int newLen = cipher.update(dup, bb);
            if (newLen != len) {
                // catch BouncyCastle buffering error
                throw new RuntimeException("Cipher buffering error " +
                    "in JCE provider " + cipher.getProvider().getName());
            }

            if (debug != null && Debug.isOn("plaintext")) {
                try {
                    HexDumpEncoder hd = new HexDumpEncoder();

                    System.out.println(
                        "Padded plaintext after DECRYPTION:  len = "
                        + newLen);

                    hd.encodeBuffer(
                        (ByteBuffer)bb.duplicate().position(pos), System.out);
                } catch (IOException e) { }
            }

            /*
             * Remove the block padding.
             */
            if (blockSize != 0) {
                bb.position(pos);
                newLen = removePadding(
                    bb, tagLen, blockSize, protocolVersion);

                if (protocolVersion.v >= ProtocolVersion.TLS11.v) {
                    if (newLen < blockSize) {
                        throw new BadPaddingException("invalid explicit IV");
                    }

                    // discards the first cipher block, the IV component.
                    byte[] buf = null;
                    int limit = bb.limit();
                    if (bb.hasArray()) {
                        int arrayOffset = bb.arrayOffset();
                        buf = bb.array();
                        System.arraycopy(buf, arrayOffset + pos + blockSize,
                            buf, arrayOffset + pos, limit - pos - blockSize);
                        bb.limit(limit - blockSize);
                    } else {
                        buf = new byte[limit - pos - blockSize];
                        bb.position(pos + blockSize);
                        bb.get(buf);
                        bb.position(pos);
                        bb.put(buf);
                        bb.limit(limit - blockSize);
                    }

                    // reset the position to the end of the decrypted data
                    limit = bb.limit();
                    bb.position(limit);
                }
            }
            return newLen;
        } catch (ShortBufferException e) {
            RuntimeException exc = new RuntimeException(e.toString());
            exc.initCause(e);
            throw exc;
        }
    }

    private static int addPadding(byte[] buf, int offset, int len,
            int blockSize) {
        int     newlen = len + 1;
        byte    pad;
        int     i;

        if ((newlen % blockSize) != 0) {
            newlen += blockSize - 1;
            newlen -= newlen % blockSize;
        }
        pad = (byte) (newlen - len);

        if (buf.length < (newlen + offset)) {
            throw new IllegalArgumentException("no space to pad buffer");
        }

        /*
         * TLS version of the padding works for both SSLv3 and TLSv1
         */
        for (i = 0, offset += len; i < pad; i++) {
            buf [offset++] = (byte) (pad - 1);
        }
        return newlen;
    }

    /*
     * Apply the padding to the buffer.
     *
     * Limit is advanced to the new buffer length.
     * Position is equal to limit.
     */
    private static int addPadding(ByteBuffer bb, int blockSize) {

        int     len = bb.remaining();
        int     offset = bb.position();

        int     newlen = len + 1;
        byte    pad;
        int     i;

        if ((newlen % blockSize) != 0) {
            newlen += blockSize - 1;
            newlen -= newlen % blockSize;
        }
        pad = (byte) (newlen - len);

        /*
         * Update the limit to what will be padded.
         */
        bb.limit(newlen + offset);

        /*
         * TLS version of the padding works for both SSLv3 and TLSv1
         */
        for (i = 0, offset += len; i < pad; i++) {
            bb.put(offset++, (byte) (pad - 1));
        }

        bb.position(offset);
        bb.limit(offset);

        return newlen;
    }

    /*
     * A constant-time check of the padding.
     *
     * NOTE that we are checking both the padding and the padLen bytes here.
     *
     * The caller MUST ensure that the len parameter is a positive number.
     */
    private static int[] checkPadding(
            byte[] buf, int offset, int len, byte pad) {

        if (len <= 0) {
            throw new RuntimeException("padding len must be positive");
        }

        // An array of hits is used to prevent Hotspot optimization for
        // the purpose of a constant-time check
        int[] results = {0, 0};    // {missed #, matched #}
        for (int i = 0; i <= 256;) {
            for (int j = 0; j < len && i <= 256; j++, i++) {     // j <= i
                if (buf[offset + j] != pad) {
                    results[0]++;       // mismatched padding data
                } else {
                    results[1]++;       // matched padding data
                }
            }
        }

        return results;
    }

    /*
     * A constant-time check of the padding.
     *
     * NOTE that we are checking both the padding and the padLen bytes here.
     *
     * The caller MUST ensure that the bb parameter has remaining.
     */
    private static int[] checkPadding(ByteBuffer bb, byte pad) {

        if (!bb.hasRemaining()) {
            throw new RuntimeException("hasRemaining() must be positive");
        }

        // An array of hits is used to prevent Hotspot optimization for
        // the purpose of a constant-time check.
        int[] results = {0, 0};    // {missed #, matched #}
        bb.mark();
        for (int i = 0; i <= 256; bb.reset()) {
            for (; bb.hasRemaining() && i <= 256; i++) {
                if (bb.get() != pad) {
                    results[0]++;       // mismatched padding data
                } else {
                    results[1]++;       // matched padding data
                }
            }
        }

        return results;
    }

    /*
     * Typical TLS padding format for a 64 bit block cipher is as follows:
     *   xx xx xx xx xx xx xx 00
     *   xx xx xx xx xx xx 01 01
     *   ...
     *   xx 06 06 06 06 06 06 06
     *   07 07 07 07 07 07 07 07
     * TLS also allows any amount of padding from 1 and 256 bytes as long
     * as it makes the data a multiple of the block size
     */
    private static int removePadding(byte[] buf, int offset, int len,
            int tagLen, int blockSize,
            ProtocolVersion protocolVersion) throws BadPaddingException {

        // last byte is length byte (i.e. actual padding length - 1)
        int padOffset = offset + len - 1;
        int padLen = buf[padOffset] & 0xFF;

        int newLen = len - (padLen + 1);
        if ((newLen - tagLen) < 0) {
            // If the buffer is not long enough to contain the padding plus
            // a MAC tag, do a dummy constant-time padding check.
            //
            // Note that it is a dummy check, so we won't care about what is
            // the actual padding data.
            checkPadding(buf, offset, len, (byte)(padLen & 0xFF));

            throw new BadPaddingException("Invalid Padding length: " + padLen);
        }

        // The padding data should be filled with the padding length value.
        int[] results = checkPadding(buf, offset + newLen,
                        padLen + 1, (byte)(padLen & 0xFF));
        if (protocolVersion.v >= ProtocolVersion.TLS10.v) {
            if (results[0] != 0) {          // padding data has invalid bytes
                throw new BadPaddingException("Invalid TLS padding data");
            }
        } else { // SSLv3
            // SSLv3 requires 0 <= length byte < block size
            // some implementations do 1 <= length byte <= block size,
            // so accept that as well
            // v3 does not require any particular value for the other bytes
            if (padLen > blockSize) {
                throw new BadPaddingException("Invalid SSLv3 padding");
            }
        }
        return newLen;
    }

    /*
     * Position/limit is equal the removed padding.
     */
    private static int removePadding(ByteBuffer bb,
            int tagLen, int blockSize,
            ProtocolVersion protocolVersion) throws BadPaddingException {

        int len = bb.remaining();
        int offset = bb.position();

        // last byte is length byte (i.e. actual padding length - 1)
        int padOffset = offset + len - 1;
        int padLen = bb.get(padOffset) & 0xFF;

        int newLen = len - (padLen + 1);
        if ((newLen - tagLen) < 0) {
            // If the buffer is not long enough to contain the padding plus
            // a MAC tag, do a dummy constant-time padding check.
            //
            // Note that it is a dummy check, so we won't care about what is
            // the actual padding data.
            checkPadding(bb.duplicate(), (byte)(padLen & 0xFF));

            throw new BadPaddingException("Invalid Padding length: " + padLen);
        }

        // The padding data should be filled with the padding length value.
        int[] results = checkPadding(
                (ByteBuffer)bb.duplicate().position(offset + newLen),
                (byte)(padLen & 0xFF));
        if (protocolVersion.v >= ProtocolVersion.TLS10.v) {
            if (results[0] != 0) {          // padding data has invalid bytes
                throw new BadPaddingException("Invalid TLS padding data");
            }
        } else { // SSLv3
            // SSLv3 requires 0 <= length byte < block size
            // some implementations do 1 <= length byte <= block size,
            // so accept that as well
            // v3 does not require any particular value for the other bytes
           if (padLen > blockSize) {
                throw new BadPaddingException("Invalid SSLv3 padding");
            }
        }

        /*
         * Reset buffer limit to remove padding.
         */
        bb.position(offset + newLen);
        bb.limit(offset + newLen);

        return newLen;
    }

    /*
     * Does the cipher use CBC mode?
     *
     * @return true if the cipher use CBC mode, false otherwise.
     */
    boolean isCBCMode() {
        return isCBCMode;
    }

    Is the cipher null?
Returns: true if the cipher is null, false otherwise./**
     * Is the cipher null?
     *
     * @return true if the cipher is null, false otherwise.
     */
    boolean isNullCipher() {
        return cipher == null;
    }

    Sanity check the length of a fragment before decryption.
In CBC mode, check that the fragment length is one or multiple times
of the block size of the cipher suite, and is at least one (one is the
smallest size of padding in CBC mode) bigger than the tag size of the
MAC algorithm.
In non-CBC mode, check that the fragment length is not less than the
tag size of the MAC algorithm.
Returns: true if the length of a fragment matches above requirements/**
     * Sanity check the length of a fragment before decryption.
     *
     * In CBC mode, check that the fragment length is one or multiple times
     * of the block size of the cipher suite, and is at least one (one is the
     * smallest size of padding in CBC mode) bigger than the tag size of the
     * MAC algorithm.
     *
     * In non-CBC mode, check that the fragment length is not less than the
     * tag size of the MAC algorithm.
     *
     * @return true if the length of a fragment matches above requirements
     */
    boolean sanityCheck(int tagLen, int fragmentLen) {
        if (!isCBCMode) {
            return fragmentLen >= tagLen;
        }

        if ((fragmentLen % blockSize) == 0) {
            int minimal = tagLen + 1;
            minimal = (minimal >= blockSize) ? minimal : blockSize;
            return (fragmentLen >= minimal);
        }

        return false;
    }
}
/

java/ 6/ sun/security/ssl/CipherBox.java
