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- fixes #7

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- removes any use of CBC mode (might affect issue #9)
This commit is contained in:
Sebastian Stenzel 2014-12-30 17:38:57 +01:00
parent 4f91adb822
commit d8c9279f6f
3 changed files with 44 additions and 26 deletions
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51
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/Aes256Cryptor.java
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@ -74,8 +74,8 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
private static final SecretKeyFactory PBKDF2_FACTORY;
/**
* Defined in static initializer. Defaults to 256, but falls back to maximum value possible, if JCE isn't installed. JCE can be
* installed from here: http://www.oracle.com/technetwork/java/javase/downloads/.
* Defined in static initializer. Defaults to 256, but falls back to maximum value possible, if JCE Unlimited Strength Jurisdiction
* Policy Files isn't installed. Those files can be downloaded here: http://www.oracle.com/technetwork/java/javase/downloads/.
*/
private static final int AES_KEY_LENGTH;
@ -227,11 +227,11 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
return result;
}
private SecretKey pbkdf2(byte[] password, byte[] salt, int iterations, int keyLength) {
final char[] pw = new char[password.length];
private SecretKey deriveSecretKeyFromMasterKey() {
final char[] pw = new char[masterKey.length];
try {
byteToChar(password, pw);
return pbkdf2(CharBuffer.wrap(pw), salt, iterations, keyLength);
byteToChar(masterKey, pw);
return pbkdf2(CharBuffer.wrap(pw), EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
} finally {
Arrays.fill(pw, (char) 0);
}
@ -271,7 +271,7 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
@Override
public String encryptPath(String cleartextPath, char encryptedPathSep, char cleartextPathSep, CryptorIOSupport ioSupport) {
try {
final SecretKey key = this.pbkdf2(masterKey, EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
final SecretKey key = this.deriveSecretKeyFromMasterKey();
final String[] cleartextPathComps = StringUtils.split(cleartextPath, cleartextPathSep);
final List<String> encryptedPathComps = new ArrayList<>(cleartextPathComps.length);
for (final String cleartext : cleartextPathComps) {
@ -300,27 +300,30 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
* {@link FileNamingConventions#LONG_NAME_FILE_EXT}.
*/
private String encryptPathComponent(final String cleartext, final SecretKey key, CryptorIOSupport ioSupport) throws IllegalBlockSizeException, BadPaddingException, IOException {
final Cipher cipher = this.cipher(FILE_NAME_CIPHER, key, EMPTY_IV, Cipher.ENCRYPT_MODE);
final byte[] ivRandomPart = randomData(FILE_NAME_IV_LENGTH);
final ByteBuffer iv = ByteBuffer.allocate(AES_BLOCK_LENGTH);
iv.put(ivRandomPart);
final Cipher cipher = this.cipher(FILE_NAME_CIPHER, key, iv.array(), Cipher.ENCRYPT_MODE);
final byte[] cleartextBytes = cleartext.getBytes(Charsets.UTF_8);
final byte[] encryptedBytes = cipher.doFinal(cleartextBytes);
final String encrypted = ENCRYPTED_FILENAME_CODEC.encodeAsString(encryptedBytes) + BASIC_FILE_EXT;
final String ivAndCiphertext = ENCRYPTED_FILENAME_CODEC.encodeAsString(ivRandomPart) + IV_PREFIX_SEPARATOR + ENCRYPTED_FILENAME_CODEC.encodeAsString(encryptedBytes);
if (encrypted.length() > ENCRYPTED_FILENAME_LENGTH_LIMIT) {
final String crc32 = Long.toHexString(crc32Sum(encrypted.getBytes()));
if (ivAndCiphertext.length() + BASIC_FILE_EXT.length() > ENCRYPTED_FILENAME_LENGTH_LIMIT) {
final String crc32 = Long.toHexString(crc32Sum(ivAndCiphertext.getBytes()));
final String metadataFilename = crc32 + METADATA_FILE_EXT;
final LongFilenameMetadata metadata = this.getMetadata(ioSupport, metadataFilename);
final String alternativeFileName = crc32 + LONG_NAME_PREFIX_SEPARATOR + metadata.getOrCreateUuidForEncryptedFilename(encrypted).toString() + LONG_NAME_FILE_EXT;
final String alternativeFileName = crc32 + LONG_NAME_PREFIX_SEPARATOR + metadata.getOrCreateUuidForEncryptedFilename(ivAndCiphertext).toString() + LONG_NAME_FILE_EXT;
this.storeMetadata(ioSupport, metadataFilename, metadata);
return alternativeFileName;
} else {
return encrypted;
return ivAndCiphertext + BASIC_FILE_EXT;
}
}
@Override
public String decryptPath(String encryptedPath, char encryptedPathSep, char cleartextPathSep, CryptorIOSupport ioSupport) {
try {
final SecretKey key = this.pbkdf2(masterKey, EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
final SecretKey key = this.deriveSecretKeyFromMasterKey();
final String[] encryptedPathComps = StringUtils.split(encryptedPath, encryptedPathSep);
final List<String> cleartextPathComps = new ArrayList<>(encryptedPathComps.length);
for (final String encrypted : encryptedPathComps) {
@ -337,21 +340,27 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
* @see #encryptPathComponent(String, SecretKey, CryptorIOSupport)
*/
private String decryptPathComponent(final String encrypted, final SecretKey key, CryptorIOSupport ioSupport) throws IllegalBlockSizeException, BadPaddingException, IOException {
final String ciphertext;
final String ivAndCiphertext;
if (encrypted.endsWith(LONG_NAME_FILE_EXT)) {
final String basename = StringUtils.removeEnd(encrypted, LONG_NAME_FILE_EXT);
final String crc32 = StringUtils.substringBefore(basename, LONG_NAME_PREFIX_SEPARATOR);
final String uuid = StringUtils.substringAfter(basename, LONG_NAME_PREFIX_SEPARATOR);
final String metadataFilename = crc32 + METADATA_FILE_EXT;
final LongFilenameMetadata metadata = this.getMetadata(ioSupport, metadataFilename);
ciphertext = metadata.getEncryptedFilenameForUUID(UUID.fromString(uuid));
ivAndCiphertext = metadata.getEncryptedFilenameForUUID(UUID.fromString(uuid));
} else if (encrypted.endsWith(BASIC_FILE_EXT)) {
ciphertext = StringUtils.removeEndIgnoreCase(encrypted, BASIC_FILE_EXT);
ivAndCiphertext = StringUtils.removeEndIgnoreCase(encrypted, BASIC_FILE_EXT);
} else {
throw new IllegalArgumentException("Unsupported path component: " + encrypted);
}
final Cipher cipher = this.cipher(FILE_NAME_CIPHER, key, EMPTY_IV, Cipher.DECRYPT_MODE);
final String ivRandomPartStr = StringUtils.substringBefore(ivAndCiphertext, IV_PREFIX_SEPARATOR);
final String ciphertext = StringUtils.substringAfter(ivAndCiphertext, IV_PREFIX_SEPARATOR);
final byte[] ivRandomPart = ENCRYPTED_FILENAME_CODEC.decode(ivRandomPartStr);
final ByteBuffer iv = ByteBuffer.allocate(AES_BLOCK_LENGTH);
iv.put(ivRandomPart);
final Cipher cipher = this.cipher(FILE_NAME_CIPHER, key, iv.array(), Cipher.DECRYPT_MODE);
final byte[] encryptedBytes = ENCRYPTED_FILENAME_CODEC.decode(ciphertext);
final byte[] cleartextBytes = cipher.doFinal(encryptedBytes);
return new String(cleartextBytes, Charsets.UTF_8);
@ -394,7 +403,7 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
}
// derive secret key and generate cipher:
final SecretKey key = this.pbkdf2(masterKey, EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
final SecretKey key = this.deriveSecretKeyFromMasterKey();
final Cipher cipher = this.cipher(FILE_CONTENT_CIPHER, key, countingIv.array(), Cipher.DECRYPT_MODE);
// read content
@ -425,7 +434,7 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
encryptedFile.position(SIZE_OF_LONG + AES_BLOCK_LENGTH + beginOfFirstRelevantBlock);
// derive secret key and generate cipher:
final SecretKey key = this.pbkdf2(masterKey, EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
final SecretKey key = this.deriveSecretKeyFromMasterKey();
final Cipher cipher = this.cipher(FILE_CONTENT_CIPHER, key, countingIv.array(), Cipher.DECRYPT_MODE);
// read content
@ -445,7 +454,7 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
countingIv.position(0);
// derive secret key and generate cipher:
final SecretKey key = this.pbkdf2(masterKey, EMPTY_SALT, PBKDF2_MASTERKEY_ITERATIONS, AES_KEY_LENGTH);
final SecretKey key = this.deriveSecretKeyFromMasterKey();
final Cipher cipher = this.cipher(FILE_CONTENT_CIPHER, key, countingIv.array(), Cipher.ENCRYPT_MODE);
// 8 bytes (file size: temporarily -1):

14
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/AesCryptographicConfiguration.java
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@ -31,7 +31,10 @@ interface AesCryptographicConfiguration {
byte[] EMPTY_SALT = new byte[SALT_LENGTH];
/**
* Algorithm used for key derivation.
* Algorithm used for key derivation as defined in RFC 2898 / PKCS #5.
*
* SHA1 will deprecate soon, but the main purpose of PBKDF2 is waisting CPU cycles, so cryptographically strong hash algorithms are not
* necessary here. See also http://crypto.stackexchange.com/a/11017
*/
String KEY_FACTORY_ALGORITHM = "PBKDF2WithHmacSHA1";
@ -52,14 +55,14 @@ interface AesCryptographicConfiguration {
*
* @see http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#Cipher
*/
String MASTERKEY_CIPHER = "AES/CBC/PKCS5Padding";
String MASTERKEY_CIPHER = "AES/CTR/NoPadding";
/**
* Cipher specs for file name encryption.
*
* @see http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#Cipher
*/
String FILE_NAME_CIPHER = "AES/CBC/PKCS5Padding";
String FILE_NAME_CIPHER = "AES/CTR/NoPadding";
/**
* Cipher specs for content encryption. Using CTR-mode for random access.
@ -74,9 +77,10 @@ interface AesCryptographicConfiguration {
int AES_BLOCK_LENGTH = 16;
/**
* 0-filled initialization vector.
* Number of non-zero bytes in the IV used for file name encryption. Less means shorter encrypted filenames, more means higher entropy.
* Maximum length is {@value #AES_BLOCK_LENGTH}.
*/
byte[] EMPTY_IV = new byte[AES_BLOCK_LENGTH];
int FILE_NAME_IV_LENGTH = 4;
/**
* Number of iterations for key derived from user pw. High iteration count for better resistance to bruteforcing.

5
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/FileNamingConventions.java
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@ -37,6 +37,11 @@ interface FileNamingConventions {
*/
String BASIC_FILE_EXT = ".aes";
/**
* Prefix in front of the actual encrypted file name used as IV.
*/
String IV_PREFIX_SEPARATOR = "_";
/**
* For plaintext file names > {@value #ENCRYPTED_FILENAME_LENGTH_LIMIT} chars.
*/