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package javax.crypto.spec;

import java.security.spec.AlgorithmParameterSpec;

/**

 * Specifies the set of parameters required by a {@link

 * javax.crypto.Cipher} using the Galois/Counter Mode (GCM) mode.

 * <p>

 * Simple block cipher modes (such as CBC) generally require only an

 * initialization vector (such as {@code IvParameterSpec}),

 * but GCM needs these parameters:

 * <ul>

 * <li>{@code IV}: Initialization Vector (IV) </li>

 * <li>{@code tLen}: length (in bits) of authentication tag T</li>

 * </ul>

 * <p>

 * In addition to the parameters described here, other GCM inputs/output

 * (Additional Authenticated Data (AAD), Keys, block ciphers,

 * plain/ciphertext and authentication tags) are handled in the {@code

 * Cipher} class.

 * <p>

 * Please see <a href="http://www.ietf.org/rfc/rfc5116.txt"> RFC 5116

 * </a> for more information on the Authenticated Encryption with

 * Associated Data (AEAD) algorithm, and <a href=

 * "http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf">

 * NIST Special Publication 800-38D</a>, "NIST Recommendation for Block

 * Cipher Modes of Operation:  Galois/Counter Mode (GCM) and GMAC."

 * <p>

 * The GCM specification states that {@code tLen} may only have the

 * values {128, 120, 112, 104, 96}, or {64, 32} for certain

 * applications.  Other values can be specified for this class, but not

 * all CSP implementations will support them.

 *

 * @see javax.crypto.Cipher

 *

 * @since 1.7

 */

public class GCMParameterSpec implements AlgorithmParameterSpec {

    // Initialization Vector.  Could use IvParameterSpec, but that

    // would add extra copies.

    private byte[] iv;

    // Required Tag length (in bits).

    private int tLen;

    /**

     * Constructs a GCMParameterSpec using the specified authentication

     * tag bit-length and IV buffer.

     *

     * @param tLen the authentication tag length (in bits)

     * @param src the IV source buffer.  The contents of the buffer are

     * copied to protect against subsequent modification.

     *

     * @throws IllegalArgumentException if {@code tLen} is negative,

     * or {@code src} is null.

     */

    public GCMParameterSpec(int tLen, byte[] src) {

        if (src == null) {

            throw new IllegalArgumentException("src array is null");

        }

        init(tLen, src, 0, src.length);

    }

    /**

     * Constructs a GCMParameterSpec object using the specified

     * authentication tag bit-length and a subset of the specified

     * buffer as the IV.

     *

     * @param tLen the authentication tag length (in bits)

     * @param src the IV source buffer.  The contents of the

     * buffer are copied to protect against subsequent modification.

     * @param offset the offset in {@code src} where the IV starts

     * @param len the number of IV bytes

     *

     * @throws IllegalArgumentException if {@code tLen} is negative,

     * {@code src} is null, {@code len} or {@code offset} is negative,

     * or the sum of {@code offset} and {@code len} is greater than the

     * length of the {@code src} byte array.

     */

    public GCMParameterSpec(int tLen, byte[] src, int offset, int len) {

        init(tLen, src, offset, len);

    }

    /*

     * Check input parameters.

     */

    private void init(int tLen, byte[] src, int offset, int len) {

        if (tLen < 0) {

            throw new IllegalArgumentException(

                "Length argument is negative");

        }

        this.tLen = tLen;

        // Input sanity check

        if ((src == null) ||(len < 0) || (offset < 0)

                || (len > (src.length - offset))) {

            throw new IllegalArgumentException("Invalid buffer arguments");

        }

        iv = new byte[len];

        System.arraycopy(src, offset, iv, 0, len);

    }

    /**

     * Returns the authentication tag length.

     *

     * @return the authentication tag length (in bits)

     */

    public int getTLen() {

        return tLen;

    }

    /**

     * Returns the Initialization Vector (IV).

     *

     * @return the IV.  Creates a new array each time this method

     * is called.

     */

    public byte[] getIV() {

        return iv.clone();

    }

}