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package com.nimbusds.jose.crypto;
import java.nio.ByteBuffer;
import java.security.Provider;
import java.security.SecureRandom;
import java.util.Arrays;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import net.jcip.annotations.ThreadSafe;
import com.nimbusds.jose.JOSEException;
import com.nimbusds.jose.JWEHeader;
import com.nimbusds.jose.util.Base64URL;
/**
* AES/CBC/PKCS5Padding and AES/CBC/PKCS5Padding/HMAC-SHA2 encryption and
* decryption methods. This class is thread-safe.
*
* Also supports the deprecated AES/CBC/HMAC encryption using a custom
* concat KDF (JOSE draft suite 08).
*
*
See draft-ietf-jose-json-web-algorithms-26, section 5.2.
*
* @author Vladimir Dzhuvinov
* @author Axel Nennker
* @version $version$ (2014-07-08)
*/
@ThreadSafe
class AESCBC {
/**
* The standard Initialisation Vector (IV) length (128 bits).
*/
public static final int IV_BIT_LENGTH = 128;
/**
* Generates a random 128 bit (16 byte) Initialisation Vector(IV) for
* use in AES-CBC encryption.
*
* @param randomGen The secure random generator to use. Must be
* correctly initialised and not {@code null}.
*
* @return The random 128 bit IV, as 16 byte array.
*/
public static byte[] generateIV(final SecureRandom randomGen) {
byte[] bytes = new byte[IV_BIT_LENGTH / 8];
randomGen.nextBytes(bytes);
return bytes;
}
/**
* Creates a new AES/CBC/PKCS5Padding cipher.
*
* @param secretKey The AES key. Must not be {@code null}.
* @param forEncryption If {@code true} creates an encryption cipher,
* else creates a decryption cipher.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param provider The JCA provider, or {@code null} to use the
* default one.
*
* @return The AES/CBC/PKCS5Padding cipher.
*/
private static Cipher createAESCBCCipher(final SecretKey secretKey,
final boolean forEncryption,
final byte[] iv,
final Provider provider)
throws JOSEException {
Cipher cipher;
try {
cipher = CipherHelper.getInstance("AES/CBC/PKCS5Padding", provider);
SecretKeySpec keyspec = new SecretKeySpec(secretKey.getEncoded(), "AES");
IvParameterSpec ivSpec = new IvParameterSpec(iv);
if (forEncryption) {
cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivSpec);
} else {
cipher.init(Cipher.DECRYPT_MODE, keyspec, ivSpec);
}
} catch (Exception e) {
throw new JOSEException(e.getMessage(), e);
}
return cipher;
}
/**
* Encrypts the specified plain text using AES/CBC/PKCS5Padding.
*
* @param secretKey The AES key. Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param plainText The plain text. Must not be {@code null}.
* @param provider The JCA provider, or {@code null} to use the
* default one.
*
* @return The cipher text.
*
* @throws JOSEException If encryption failed.
*/
public static byte[] encrypt(final SecretKey secretKey,
final byte[] iv,
final byte[] plainText,
final Provider provider)
throws JOSEException {
Cipher cipher = createAESCBCCipher(secretKey, true, iv, provider);
try {
return cipher.doFinal(plainText);
} catch (Exception e) {
throw new JOSEException(e.getMessage(), e);
}
}
/**
* Computes the bit length of the specified Additional Authenticated
* Data (AAD). Used in AES/CBC/PKCS5Padding/HMAC-SHA2 encryption.
*
* @param aad The Additional Authenticated Data (AAD). Must not be
* {@code null}.
*
* @return The computed AAD bit length, as a 64 bit big-ending
* representation (8 byte array).
*/
public static byte[] computeAADLength(final byte[] aad) {
final int bitLength = aad.length * 8;
return ByteBuffer.allocate(8).putLong(bitLength).array();
}
/**
* Encrypts the specified plain text using AES/CBC/PKCS5Padding/
* HMAC-SHA2.
*
*
See draft-ietf-jose-json-web-algorithms-26, section 5.2.
*
*
See draft-mcgrew-aead-aes-cbc-hmac-sha2-01
*
* @param secretKey The secret key. Must be 256 or 512 bits long.
* Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param plainText The plain text. Must not be {@code null}.
* @param aad The additional authenticated data. Must not be
* {@code null}.
* @param ceProvider The JCA provider for the content encryption, or
* {@code null} to use the default one.
* @param macProvider The JCA provider for the MAC computation, or
* {@code null} to use the default one.
*
* @return The authenticated cipher text.
*
* @throws JOSEException If encryption failed.
*/
public static AuthenticatedCipherText encryptAuthenticated(final SecretKey secretKey,
final byte[] iv,
final byte[] plainText,
final byte[] aad,
final Provider ceProvider,
final Provider macProvider)
throws JOSEException {
// Extract MAC + AES/CBC keys from input secret key
CompositeKey compositeKey = new CompositeKey(secretKey);
// Encrypt plain text
byte[] cipherText = encrypt(compositeKey.getAESKey(), iv, plainText, ceProvider);
// AAD length to 8 byte array
byte[] al = computeAADLength(aad);
// Do MAC
int hmacInputLength = aad.length + iv.length + cipherText.length + al.length;
byte[] hmacInput = ByteBuffer.allocate(hmacInputLength).put(aad).put(iv).put(cipherText).put(al).array();
byte[] hmac = HMAC.compute(compositeKey.getMACKey(), hmacInput, macProvider);
byte[] authTag = Arrays.copyOf(hmac, compositeKey.getTruncatedMACByteLength());
return new AuthenticatedCipherText(cipherText, authTag);
}
/**
* Encrypts the specified plain text using the deprecated concat KDF
* from JOSE draft suite 09.
*
* @param header The JWE header. Must not be {@code null}.
* @param secretKey The secret key. Must be 256 or 512 bits long.
* Must not be {@code null}.
* @param encryptedKey The encrypted key. Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param plainText The plain text. Must not be {@code null}.
* @param ceProvider The JCA provider for the content encryption, or
* {@code null} to use the default one.
* @param macProvider The JCA provider for the MAC computation, or
* {@code null} to use the default one.
*
* @return The authenticated cipher text.
*
* @throws JOSEException If encryption failed.
*/
public static AuthenticatedCipherText encryptWithConcatKDF(final JWEHeader header,
final SecretKey secretKey,
final Base64URL encryptedKey,
final byte[] iv,
final byte[] plainText,
final Provider ceProvider,
final Provider macProvider)
throws JOSEException {
byte[] epu = null;
if (header.getCustomParam("epu") instanceof String) {
epu = new Base64URL((String)header.getCustomParam("epu")).decode();
}
byte[] epv = null;
if (header.getCustomParam("epv") instanceof String) {
epv = new Base64URL((String)header.getCustomParam("epv")).decode();
}
// Generate alternative CEK using concat-KDF
SecretKey altCEK = ConcatKDF.generateCEK(secretKey, header.getEncryptionMethod(), epu, epv);
byte[] cipherText = AESCBC.encrypt(altCEK, iv, plainText, ceProvider);
// Generate content integrity key for HMAC
SecretKey cik = ConcatKDF.generateCIK(secretKey, header.getEncryptionMethod(), epu, epv);
String macInput = header.toBase64URL().toString() + "." +
encryptedKey.toString() + "." +
Base64URL.encode(iv).toString() + "." +
Base64URL.encode(cipherText);
byte[] mac = HMAC.compute(cik, macInput.getBytes(), macProvider);
return new AuthenticatedCipherText(cipherText, mac);
}
/**
* Decrypts the specified cipher text using AES/CBC/PKCS5Padding.
*
* @param secretKey The AES key. Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param cipherText The cipher text. Must not be {@code null}.
* @param provider The JCA provider, or {@code null} to use the
* default one.
*
* @return The decrypted plain text.
*
* @throws JOSEException If decryption failed.
*/
public static byte[] decrypt(final SecretKey secretKey,
final byte[] iv,
final byte[] cipherText,
final Provider provider)
throws JOSEException {
Cipher cipher = createAESCBCCipher(secretKey, false, iv, provider);
try {
return cipher.doFinal(cipherText);
} catch (Exception e) {
throw new JOSEException(e.getMessage(), e);
}
}
/**
* Decrypts the specified cipher text using AES/CBC/PKCS5Padding/
* HMAC-SHA2.
*
*
See draft-ietf-jose-json-web-algorithms-26, section 5.2.
*
*
See draft-mcgrew-aead-aes-cbc-hmac-sha2-01
*
* @param secretKey The secret key. Must be 256 or 512 bits long.
* Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param cipherText The cipher text. Must not be {@code null}.
* @param aad The additional authenticated data. Must not be
* {@code null}.
* @param authTag The authentication tag. Must not be {@code null}.
* @param ceProvider The JCA provider for the content encryption, or
* {@code null} to use the default one.
* @param macProvider The JCA provider for the MAC computation, or
* {@code null} to use the default one.
*
* @return The decrypted plain text.
*
* @throws JOSEException If decryption failed.
*/
public static byte[] decryptAuthenticated(final SecretKey secretKey,
final byte[] iv,
final byte[] cipherText,
final byte[] aad,
final byte[] authTag,
final Provider ceProvider,
final Provider macProvider)
throws JOSEException {
// Extract MAC + AES/CBC keys from input secret key
CompositeKey compositeKey = new CompositeKey(secretKey);
// AAD length to 8 byte array
byte[] al = computeAADLength(aad);
// Check MAC
int hmacInputLength = aad.length + iv.length + cipherText.length + al.length;
byte[] hmacInput = ByteBuffer.allocate(hmacInputLength).put(aad).put(iv).put(cipherText).put(al).array();
byte[] hmac = HMAC.compute(compositeKey.getMACKey(), hmacInput, macProvider);
byte[] expectedAuthTag = Arrays.copyOf(hmac, compositeKey.getTruncatedMACByteLength());
boolean macCheckPassed = true;
if (! ConstantTimeUtils.areEqual(expectedAuthTag, authTag)) {
// Thwart timing attacks by delaying exception until after decryption
macCheckPassed = false;
}
byte[] plainText = decrypt(compositeKey.getAESKey(), iv, cipherText, ceProvider);
if (! macCheckPassed) {
throw new JOSEException("MAC check failed");
}
return plainText;
}
/**
* Decrypts the specified cipher text using the deprecated concat KDF
* from JOSE draft suite 09.
*
* @param header The JWE header. Must not be {@code null}.
* @param secretKey The secret key. Must be 256 or 512 bits long.
* Must not be {@code null}.
* @param encryptedKey The encrypted key. Must not be {@code null}.
* @param iv The initialisation vector (IV). Must not be
* {@code null}.
* @param cipherText The cipher text. Must not be {@code null}.
* @param authTag The authentication tag. Must not be {@code null}.
* @param ceProvider The JCA provider for the content encryption, or
* {@code null} to use the default one.
* @param macProvider The JCA provider for the MAC computation, or
* {@code null} to use the default one.
*
* @return The decrypted plain text.
*
* @throws JOSEException If decryption failed.
*/
public static byte[] decryptWithConcatKDF(final JWEHeader header,
final SecretKey secretKey,
final Base64URL encryptedKey,
final Base64URL iv,
final Base64URL cipherText,
final Base64URL authTag,
final Provider ceProvider,
final Provider macProvider)
throws JOSEException {
byte[] epu = null;
if (header.getCustomParam("epu") instanceof String) {
epu = new Base64URL((String)header.getCustomParam("epu")).decode();
}
byte[] epv = null;
if (header.getCustomParam("epv") instanceof String) {
epv = new Base64URL((String)header.getCustomParam("epv")).decode();
}
SecretKey cekAlt = ConcatKDF.generateCEK(secretKey, header.getEncryptionMethod(), epu, epv);
final byte[] plainText = AESCBC.decrypt(cekAlt, iv.decode(), cipherText.decode(), ceProvider);
SecretKey cik = ConcatKDF.generateCIK(secretKey, header.getEncryptionMethod(), epu, epv);
String macInput = header.toBase64URL().toString() + "." +
encryptedKey.toString() + "." +
iv.toString() + "." +
cipherText.toString();
byte[] mac = HMAC.compute(cik, macInput.getBytes(), macProvider);
if (! ConstantTimeUtils.areEqual(authTag.decode(), mac)) {
throw new JOSEException("HMAC integrity check failed");
}
return plainText;
}
/**
* Prevents public instantiation.
*/
private AESCBC() { }
}