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Using 96 bit of random data and a 32 bit counter (as specified in https://tools.ietf.org/html/rfc3686#section-4). Thus maximum file size supported by Cryptomator is 64GiB, but decreasing risk of IV collisions to 1 : 2^48

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This commit is contained in:
Sebastian Stenzel 2015-03-14 21:58:06 +01:00
parent 188a13b202
commit 652c4cbafb
10 changed files with 126 additions and 18 deletions
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8
main/core/src/main/java/org/cryptomator/webdav/jackrabbit/EncryptedDir.java
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@ -36,6 +36,8 @@ import org.apache.jackrabbit.webdav.property.DavPropertyName;
import org.apache.jackrabbit.webdav.property.DefaultDavProperty;
import org.apache.jackrabbit.webdav.property.ResourceType;
import org.cryptomator.crypto.Cryptor;
import org.cryptomator.crypto.exceptions.CounterOverflowException;
import org.cryptomator.crypto.exceptions.EncryptFailedException;
import org.cryptomator.webdav.exceptions.DavRuntimeException;
import org.cryptomator.webdav.exceptions.DecryptFailedRuntimeException;
import org.cryptomator.webdav.exceptions.IORuntimeException;
@ -85,6 +87,12 @@ class EncryptedDir extends AbstractEncryptedNode {
} catch (IOException e) {
LOG.error("Failed to create file.", e);
throw new IORuntimeException(e);
} catch (CounterOverflowException e) {
// lets indicate this to the client as a "file too big" error
throw new DavException(DavServletResponse.SC_INSUFFICIENT_SPACE_ON_RESOURCE, e);
} catch (EncryptFailedException e) {
LOG.error("Encryption failed for unknown reasons.", e);
throw new IllegalStateException("Encryption failed for unknown reasons.", e);
} finally {
IOUtils.closeQuietly(inputContext.getInputStream());
}

3
main/core/src/main/java/org/cryptomator/webdav/jackrabbit/EncryptedFilePart.java
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@ -2,6 +2,7 @@ package org.cryptomator.webdav.jackrabbit;
import java.io.EOFException;
import java.io.IOException;
import java.nio.channels.ClosedByInterruptException;
import java.nio.channels.SeekableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
@ -171,6 +172,8 @@ class EncryptedFilePart extends EncryptedFile {
if (!authentic) {
cryptoWarningHandler.macAuthFailed(locator.getResourcePath());
}
} catch (ClosedByInterruptException ex) {
LOG.debug("Couldn't finish MAC verification due to interruption of worker thread.");
} catch (IOException e) {
LOG.error("IOException during MAC verification of " + path.toString(), e);
}

36
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/Aes256Cryptor.java
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@ -46,7 +46,10 @@ import org.apache.commons.lang3.StringUtils;
import org.bouncycastle.crypto.generators.SCrypt;
import org.cryptomator.crypto.AbstractCryptor;
import org.cryptomator.crypto.CryptorIOSupport;
import org.cryptomator.crypto.aes256.CounterAwareInputStream.CounterAwareInputLimitReachedException;
import org.cryptomator.crypto.exceptions.CounterOverflowException;
import org.cryptomator.crypto.exceptions.DecryptFailedException;
import org.cryptomator.crypto.exceptions.EncryptFailedException;
import org.cryptomator.crypto.exceptions.MacAuthenticationFailedException;
import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
import org.cryptomator.crypto.exceptions.WrongPasswordException;
@ -510,10 +513,10 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
long firstRelevantBlock = pos / AES_BLOCK_LENGTH; // cut of fraction!
long beginOfFirstRelevantBlock = firstRelevantBlock * AES_BLOCK_LENGTH;
long offsetInsideFirstRelevantBlock = pos - beginOfFirstRelevantBlock;
countingIv.putLong(AES_BLOCK_LENGTH - Long.BYTES, firstRelevantBlock);
countingIv.putInt(AES_BLOCK_LENGTH - Integer.BYTES, (int) firstRelevantBlock); // int-cast is possible, as max file size is 64GiB
// fast forward stream:
encryptedFile.position(64 + beginOfFirstRelevantBlock);
encryptedFile.position(64l + beginOfFirstRelevantBlock);
// generate cipher:
final Cipher cipher = this.aesCtrCipher(primaryMasterKey, countingIv.array(), Cipher.DECRYPT_MODE);
@ -525,13 +528,13 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
}
@Override
public Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException {
public Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException, EncryptFailedException {
// truncate file
encryptedFile.truncate(0);
// use an IV, whose last 8 bytes store a long used in counter mode and write initial value to file.
final ByteBuffer countingIv = ByteBuffer.wrap(randomData(AES_BLOCK_LENGTH));
countingIv.putLong(AES_BLOCK_LENGTH - Long.BYTES, 0l);
countingIv.putInt(AES_BLOCK_LENGTH - Integer.BYTES, 0);
encryptedFile.write(countingIv);
// init crypto stuff:
@ -550,18 +553,29 @@ public class Aes256Cryptor extends AbstractCryptor implements AesCryptographicCo
final OutputStream macOut = new MacOutputStream(out, mac);
final OutputStream cipheredOut = new CipherOutputStream(macOut, cipher);
final OutputStream blockSizeBufferedOut = new BufferedOutputStream(cipheredOut, AES_BLOCK_LENGTH);
final Long plaintextSize = IOUtils.copyLarge(plaintextFile, blockSizeBufferedOut);
final InputStream lengthLimitingIn = new CounterAwareInputStream(plaintextFile);
final Long plaintextSize;
try {
plaintextSize = IOUtils.copyLarge(lengthLimitingIn, blockSizeBufferedOut);
} catch (CounterAwareInputLimitReachedException ex) {
encryptedFile.truncate(64l + CounterAwareInputStream.SIXTY_FOUR_GIGABYE);
encryptedContentLength(encryptedFile, CounterAwareInputStream.SIXTY_FOUR_GIGABYE);
// no additional padding needed here, as 64GiB is a multiple of 128bit
throw new CounterOverflowException("File size exceeds limit (64Gib). Aborting to prevent counter overflow.");
}
// ensure total byte count is a multiple of the block size, in CTR mode:
final int remainderToFillLastBlock = AES_BLOCK_LENGTH - (int) (plaintextSize % AES_BLOCK_LENGTH);
blockSizeBufferedOut.write(new byte[remainderToFillLastBlock]);
// append a few blocks of fake data:
final int numberOfPlaintextBlocks = (int) Math.ceil(plaintextSize / AES_BLOCK_LENGTH);
final int upToTenPercentFakeBlocks = (int) Math.ceil(Math.random() * 0.1 * numberOfPlaintextBlocks);
final byte[] emptyBytes = this.randomData(AES_BLOCK_LENGTH);
for (int i = 0; i < upToTenPercentFakeBlocks; i += AES_BLOCK_LENGTH) {
blockSizeBufferedOut.write(emptyBytes);
// for filesizes of up to 16GiB: append a few blocks of fake data:
if (plaintextSize < (long) (Integer.MAX_VALUE / 4) * AES_BLOCK_LENGTH) {
final int numberOfPlaintextBlocks = (int) Math.ceil(plaintextSize / AES_BLOCK_LENGTH);
final int upToTenPercentFakeBlocks = (int) Math.ceil(Math.random() * 0.1 * numberOfPlaintextBlocks);
final byte[] emptyBytes = this.randomData(AES_BLOCK_LENGTH);
for (int i = 0; i < upToTenPercentFakeBlocks; i += AES_BLOCK_LENGTH) {
blockSizeBufferedOut.write(emptyBytes);
}
}
blockSizeBufferedOut.flush();

59
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/CounterAwareInputStream.java Normal file
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@ -0,0 +1,59 @@
package org.cryptomator.crypto.aes256;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.atomic.AtomicLong;
import javax.crypto.Mac;
/**
* Updates a {@link Mac} with the bytes read from this stream.
*/
class CounterAwareInputStream extends FilterInputStream {
static final long SIXTY_FOUR_GIGABYE = 1024l * 1024l * 1024l * 64l;
private final AtomicLong counter;
/**
* @param in Stream from which to read contents, which will update the Mac.
* @param mac Mac to be updated during writes.
*/
public CounterAwareInputStream(InputStream in) {
super(in);
this.counter = new AtomicLong(0l);
}
@Override
public int read() throws IOException {
int b = in.read();
if (b != -1) {
final long currentValue = counter.incrementAndGet();
failWhen64GibReached(currentValue);
}
return b;
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
int read = in.read(b, off, len);
if (read > 0) {
final long currentValue = counter.addAndGet(read);
failWhen64GibReached(currentValue);
}
return read;
}
private void failWhen64GibReached(long currentValue) throws CounterAwareInputLimitReachedException {
if (currentValue > SIXTY_FOUR_GIGABYE) {
throw new CounterAwareInputLimitReachedException();
}
}
static class CounterAwareInputLimitReachedException extends IOException {
private static final long serialVersionUID = -1905012809288019359L;
}
}

4
main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/MacInputStream.java
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@ -25,7 +25,9 @@ class MacInputStream extends FilterInputStream {
@Override
public int read() throws IOException {
int b = in.read();
mac.update((byte) b);
if (b != -1) {
mac.update((byte) b);
}
return b;
}

9
main/crypto-aes/src/test/java/org/cryptomator/crypto/aes256/Aes256CryptorTest.java
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@ -21,6 +21,7 @@ import java.util.Map;
import org.apache.commons.io.IOUtils;
import org.cryptomator.crypto.CryptorIOSupport;
import org.cryptomator.crypto.exceptions.DecryptFailedException;
import org.cryptomator.crypto.exceptions.EncryptFailedException;
import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
import org.cryptomator.crypto.exceptions.WrongPasswordException;
import org.junit.Assert;
@ -70,7 +71,7 @@ public class Aes256CryptorTest {
}
@Test
public void testIntegrityAuthentication() throws IOException, DecryptFailedException {
public void testIntegrityAuthentication() throws IOException, DecryptFailedException, EncryptFailedException {
// our test plaintext data:
final byte[] plaintextData = "Hello World".getBytes();
final InputStream plaintextIn = new ByteArrayInputStream(plaintextData);
@ -102,7 +103,7 @@ public class Aes256CryptorTest {
}
@Test(expected = DecryptFailedException.class)
public void testIntegrityViolationDuringDecryption() throws IOException, DecryptFailedException {
public void testIntegrityViolationDuringDecryption() throws IOException, DecryptFailedException, EncryptFailedException {
// our test plaintext data:
final byte[] plaintextData = "Hello World".getBytes();
final InputStream plaintextIn = new ByteArrayInputStream(plaintextData);
@ -134,7 +135,7 @@ public class Aes256CryptorTest {
}
@Test
public void testEncryptionAndDecryption() throws IOException, DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException {
public void testEncryptionAndDecryption() throws IOException, DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, EncryptFailedException {
// our test plaintext data:
final byte[] plaintextData = "Hello World".getBytes();
final InputStream plaintextIn = new ByteArrayInputStream(plaintextData);
@ -169,7 +170,7 @@ public class Aes256CryptorTest {
}
@Test
public void testPartialDecryption() throws IOException, DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException {
public void testPartialDecryption() throws IOException, DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, EncryptFailedException {
// our test plaintext data:
final byte[] plaintextData = new byte[65536 * Integer.BYTES];
final ByteBuffer bbIn = ByteBuffer.wrap(plaintextData);

3
main/crypto-api/src/main/java/org/cryptomator/crypto/Cryptor.java
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@ -16,6 +16,7 @@ import java.nio.file.DirectoryStream.Filter;
import java.nio.file.Path;
import org.cryptomator.crypto.exceptions.DecryptFailedException;
import org.cryptomator.crypto.exceptions.EncryptFailedException;
import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
import org.cryptomator.crypto.exceptions.WrongPasswordException;
@ -97,7 +98,7 @@ public interface Cryptor extends SensitiveDataSwipeListener {
/**
* @return Number of encrypted bytes. This might not be equal to the encrypted file size due to optional metadata written to it.
*/
Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException;
Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException, EncryptFailedException;
/**
* @return A filter, that returns <code>true</code> for encrypted files, i.e. if the file is an actual user payload and not a supporting

3
main/crypto-api/src/main/java/org/cryptomator/crypto/SamplingDecorator.java
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@ -10,6 +10,7 @@ import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.lang3.StringUtils;
import org.cryptomator.crypto.exceptions.DecryptFailedException;
import org.cryptomator.crypto.exceptions.EncryptFailedException;
import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
import org.cryptomator.crypto.exceptions.WrongPasswordException;
@ -99,7 +100,7 @@ public class SamplingDecorator implements Cryptor, CryptorIOSampling {
}
@Override
public Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException {
public Long encryptFile(InputStream plaintextFile, SeekableByteChannel encryptedFile) throws IOException, EncryptFailedException {
final InputStream countingInputStream = new CountingInputStream(encryptedBytes, plaintextFile);
return cryptor.encryptFile(countingInputStream, encryptedFile);
}

10
main/crypto-api/src/main/java/org/cryptomator/crypto/exceptions/CounterOverflowException.java Normal file
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@ -0,0 +1,10 @@
package org.cryptomator.crypto.exceptions;
public class CounterOverflowException extends EncryptFailedException {
private static final long serialVersionUID = 380066751064534731L;
public CounterOverflowException(String msg) {
super(msg);
}
}

9
main/crypto-api/src/main/java/org/cryptomator/crypto/exceptions/EncryptFailedException.java Normal file
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@ -0,0 +1,9 @@
package org.cryptomator.crypto.exceptions;
public class EncryptFailedException extends StorageCryptingException {
private static final long serialVersionUID = -3855673600374897828L;
public EncryptFailedException(String msg) {
super(msg);
}
}