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Java library for Javascript Object Signing and Encryption (JOSE) and JSON Web Tokens (JWT)
There is a newer version: 10.0.2
package com.nimbusds.jose.crypto;


import java.security.interfaces.RSAPrivateKey;
import java.util.Set;
import javax.crypto.SecretKey;

import net.jcip.annotations.ThreadSafe;

import com.nimbusds.jose.*;
import com.nimbusds.jose.jwk.RSAKey;
import com.nimbusds.jose.util.Base64URL;


/**
 * RSA decrypter of {@link com.nimbusds.jose.JWEObject JWE objects}. This class
 * is thread-safe.
 *
 * Supports the following key management algorithms:
 *
 * 

 *     {@link com.nimbusds.jose.JWEAlgorithm#RSA1_5}
 *     
{@link com.nimbusds.jose.JWEAlgorithm#RSA_OAEP}
 *     
{@link com.nimbusds.jose.JWEAlgorithm#RSA_OAEP_256}
 * 
 *
 * Supports the following content encryption algorithms:
 *
 * 

 *     {@link com.nimbusds.jose.EncryptionMethod#A128CBC_HS256}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A192CBC_HS384}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A256CBC_HS512}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A128GCM}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A192GCM}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A256GCM}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A128CBC_HS256_DEPRECATED}
 *     
{@link com.nimbusds.jose.EncryptionMethod#A256CBC_HS512_DEPRECATED}
 * 
 * 
 * @author David Ortiz
 * @author Vladimir Dzhuvinov
 * @version 2015-06-08
 */
@ThreadSafe
public class RSADecrypter extends RSACryptoProvider implements JWEDecrypter, CriticalHeaderParamsAware {


	/**
	 * The critical header policy.
	 */
	private final CriticalHeaderParamsDeferral critPolicy = new CriticalHeaderParamsDeferral();


	/**
	 * The private RSA key.
	 */
	private final RSAPrivateKey privateKey;


	/**
	 * Creates a new RSA decrypter.
	 *
	 * @param privateKey The private RSA key. Must not be {@code null}.
	 */
	public RSADecrypter(final RSAPrivateKey privateKey) {

		this(privateKey, null);
	}


	/**
	 * Creates a new RSA decrypter.
	 *
	 * @param rsaJWK The RSA JSON Web Key (JWK). Must contain a private
	 *               part. Must not be {@code null}.
	 *
	 * @throws JOSEException If the RSA JWK doesn't contain a private part
	 *                       or its extraction failed.
	 */
	public RSADecrypter(final RSAKey rsaJWK)
		throws JOSEException {

		if (! rsaJWK.isPrivate()) {
			throw new JOSEException("The RSA JWK doesn't contain a private part");
		}

		privateKey = rsaJWK.toRSAPrivateKey();
	}


	/**
	 * Creates a new RSA decrypter.
	 *
	 * @param privateKey     The private RSA key. Must not be {@code null}.
	 * @param defCritHeaders The names of the critical header parameters
	 *                       that are deferred to the application for
	 *                       processing, empty set or {@code null} if none.
	 */
	public RSADecrypter(final RSAPrivateKey privateKey,
			    final Set defCritHeaders) {

		if (privateKey == null) {
			throw new IllegalArgumentException("The private RSA key must not be null");
		}

		this.privateKey = privateKey;

		critPolicy.setDeferredCriticalHeaderParams(defCritHeaders);
	}


	/**
	 * Gets the private RSA key.
	 *
	 * @return The private RSA key.
	 */
	public RSAPrivateKey getPrivateKey() {

		return privateKey;
	}


	@Override
	public Set getProcessedCriticalHeaderParams() {

		return critPolicy.getProcessedCriticalHeaderParams();
	}


	@Override
	public Set getDeferredCriticalHeaderParams() {

		return critPolicy.getProcessedCriticalHeaderParams();
	}


	@Override
	public byte[] decrypt(final JWEHeader header,
		              final Base64URL encryptedKey,
		              final Base64URL iv,
		              final Base64URL cipherText,
		              final Base64URL authTag) 
		throws JOSEException {

		// Validate required JWE parts
		if (encryptedKey == null) {
			throw new JOSEException("Missing JWE encrypted key");
		}	

		if (iv == null) {
			throw new JOSEException("Missing JWE initialization vector (IV)");
		}

		if (authTag == null) {
			throw new JOSEException("Missing JWE authentication tag");
		}

		critPolicy.ensureHeaderPasses(header);
		

		// Derive the content encryption key
		JWEAlgorithm alg = header.getAlgorithm();

		SecretKey cek;

		if (alg.equals(JWEAlgorithm.RSA1_5)) {

			int keyLength = header.getEncryptionMethod().cekBitLength();

			// Protect against MMA attack by generating random CEK on failure,
			// see http://www.ietf.org/mail-archive/web/jose/current/msg01832.html
			final SecretKey randomCEK = ContentCryptoProvider.generateCEK(header.getEncryptionMethod(), getJCAContext().getSecureRandom());

			try {
				cek = RSA1_5.decryptCEK(privateKey, encryptedKey.decode(), keyLength, getJCAContext().getKeyEncryptionProvider());

				if (cek == null) {
					// CEK length mismatch, signalled by null instead of
					// exception to prevent MMA attack
					cek = randomCEK;
				}

			} catch (Exception e) {
				// continue
				cek = randomCEK;
			}
		
		} else if (alg.equals(JWEAlgorithm.RSA_OAEP)) {

			cek = RSA_OAEP.decryptCEK(privateKey, encryptedKey.decode(), getJCAContext().getKeyEncryptionProvider());

		} else if (alg.equals(JWEAlgorithm.RSA_OAEP_256)) {
			
			cek = RSA_OAEP_256.decryptCEK(privateKey, encryptedKey.decode(), getJCAContext().getKeyEncryptionProvider());
			
		} else {
		
			throw new JOSEException(AlgorithmSupportMessage.unsupportedJWEAlgorithm(alg, SUPPORTED_ALGORITHMS));
		}

		return ContentCryptoProvider.decrypt(header, encryptedKey, iv, cipherText, authTag, cek, getJCAContext());
	}
}