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OAuth 2.0 SDK with OpenID Connection extensions for developing client and server applications.
There is a newer version: 11.20.1
/*
 * oauth2-oidc-sdk
 *
 * Copyright 2012-2016, Connect2id Ltd and contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the
 * License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
 * CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 */

package com.nimbusds.oauth2.sdk.jose;


import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import com.nimbusds.jose.EncryptionMethod;
import com.nimbusds.jose.JOSEException;
import com.nimbusds.jose.JWEAlgorithm;
import com.nimbusds.jose.util.ByteUtils;
import com.nimbusds.oauth2.sdk.auth.Secret;


/**
 * Derives an AES secret key from a client secret. Intended for performing
 * symmetric encryption and decryption with a client secret, as specified in
 * OpenID
 * Connect Core 1.0, section 10.2.
 */
public class SecretKeyDerivation {
	
	
	/**
	 * Derives a secret encryption key from the specified client secret.
	 *
	 * @param clientSecret The client secret. Must not be {@code null}.
	 * @param alg          The JWE algorithm. Must not be {@code null}.
	 * @param enc          The JWE method. Must not be {@code null}.
	 *
	 * @return The matching secret key (with algorithm set to "AES").
	 *
	 * @throws JOSEException If the JWE algorithm or method is not
	 *                       supported.
	 */
	public static SecretKey deriveSecretKey(final Secret clientSecret,
						final JWEAlgorithm alg,
						final EncryptionMethod enc)
		throws JOSEException {
		
		if (JWEAlgorithm.DIR.equals(alg)) {
			
			int cekBitLength = enc.cekBitLength();
			
			if (cekBitLength == 0) {
				throw new JOSEException("Unsupported JWE method: enc=" + enc);
			}
			
			return deriveSecretKey(clientSecret, enc.cekBitLength());
			
		} else if (JWEAlgorithm.Family.AES_KW.contains(alg)) {
			
			if (JWEAlgorithm.A128KW.equals(alg)) {
				return deriveSecretKey(clientSecret, 128);
			} else if (JWEAlgorithm.A192KW.equals(alg)) {
				return deriveSecretKey(clientSecret, 192);
			} else if (JWEAlgorithm.A256KW.equals(alg)) {
				return deriveSecretKey(clientSecret, 256);
			}
			
		} else if (JWEAlgorithm.Family.AES_GCM_KW.contains(alg)) {
			
			if (JWEAlgorithm.A128GCMKW.equals(alg)) {
				return deriveSecretKey(clientSecret, 128);
			} else if (JWEAlgorithm.A192GCMKW.equals(alg)) {
				return deriveSecretKey(clientSecret, 192);
			} else if (JWEAlgorithm.A256GCMKW.equals(alg)) {
				return deriveSecretKey(clientSecret, 256);
			}
		}
		
		throw new JOSEException("Unsupported JWE algorithm / method: alg=" + alg + " enc=" + enc);
	}
	
	
	/**
	 * Derives a secret encryption key from the specified client secret.
	 *
	 * @param clientSecret The client secret. Must not be {@code null}.
	 * @param bits         The secret key bits (128, 192, 256, 384 or 512).
	 *
	 * @return The matching secret key (with algorithm set to "AES").
	 *
	 * @throws JOSEException If the secret key bit size it not supported.
	 */
	public static SecretKey deriveSecretKey(final Secret clientSecret, final int bits)
		throws JOSEException {
		
		final int hashBitLength;
		
		switch (bits) {
			case 128:
			case 192:
			case 256:
				hashBitLength = 256;
				break;
			case 384:
				hashBitLength = 384;
				break;
			case 512:
				hashBitLength = 512;
				break;
			default:
				throw new JOSEException("Unsupported secret key length: " + bits + " bits");
		}
		
		final byte[] hash;
		
		try {
			hash = MessageDigest.getInstance("SHA-" + hashBitLength).digest(clientSecret.getValueBytes());
		} catch (NoSuchAlgorithmException e) {
			throw new JOSEException(e.getMessage(), e);
		}
		
		final byte[] keyBytes;
		
		// If necessary remove right-most bits to fit AES key length
		// https://bitbucket.org/openid/connect/commits/15668505dbe66b290c7e84ecc2e7bff70d942012
		switch (bits) {
			case 128:
				keyBytes = ByteUtils.subArray(hash, 0, ByteUtils.byteLength(128));
				break;
			case 192:
				keyBytes = ByteUtils.subArray(hash, 0, ByteUtils.byteLength(192));
				break;
			case 256:
			case 384:
			case 512:
				keyBytes = hash;
				break;
			default:
				throw new JOSEException("Unsupported secret key length: " + bits + " bits");
		}
		
		return new SecretKeySpec(keyBytes, "AES");
	}
	
	
	/**
	 * Prevents public instantiation.
	 */
	private SecretKeyDerivation() {
	}
}