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deduplicate code
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@overheadhunter
overheadhunter committed Dec 5, 2024
1 parent 4a70475 commit 66d8d47
Showing 1 changed file with 72 additions and 52 deletions.
124 changes: 72 additions & 52 deletions src/main/java/org/cryptomator/siv/SivMode.java
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Original file line number Diff line number Diff line change
Expand Up @@ -108,22 +108,10 @@ interface CtrComputer {
* @return IV + Ciphertext as a concatenated byte array.
*/
public byte[] encrypt(SecretKey key, byte[] plaintext, byte[]... associatedData) {
final byte[] keyBytes = key.getEncoded();
if (keyBytes.length != 64 && keyBytes.length != 48 && keyBytes.length != 32) {
throw new IllegalArgumentException("Key length must be 256, 384, or 512 bits.");
}
final int subkeyLen = keyBytes.length / 2;
assert subkeyLen == 32 || subkeyLen == 24 || subkeyLen == 16;
final byte[] macKey = new byte[subkeyLen];
final byte[] ctrKey = new byte[subkeyLen];
try {
System.arraycopy(keyBytes, 0, macKey, 0, macKey.length); // K1 = leftmost(K, len(K)/2);
System.arraycopy(keyBytes, macKey.length, ctrKey, 0, ctrKey.length); // K2 = rightmost(K, len(K)/2);
return encrypt(ctrKey, macKey, plaintext, associatedData);
} finally {
Arrays.fill(macKey, (byte) 0);
Arrays.fill(ctrKey, (byte) 0);
Arrays.fill(keyBytes, (byte) 0);
return deriveSubkeysAndThen(this::encrypt, key, plaintext, associatedData);
} catch (UnauthenticCiphertextException | IllegalBlockSizeException e) {
throw new IllegalStateException("Exceptions only expected during decryption", e);
}
}

Expand All @@ -138,16 +126,10 @@ public byte[] encrypt(SecretKey key, byte[] plaintext, byte[]... associatedData)
* @throws IllegalArgumentException if keys are invalid or {@link SecretKey#getEncoded()} is not supported.
*/
public byte[] encrypt(SecretKey ctrKey, SecretKey macKey, byte[] plaintext, byte[]... associatedData) {
final byte[] ctrKeyBytes = ctrKey.getEncoded();
final byte[] macKeyBytes = macKey.getEncoded();
if (ctrKeyBytes == null || macKeyBytes == null) {
throw new IllegalArgumentException("Can't get bytes of given key.");
}
try {
return encrypt(ctrKeyBytes, macKeyBytes, plaintext, associatedData);
} finally {
Arrays.fill(ctrKeyBytes, (byte) 0);
Arrays.fill(macKeyBytes, (byte) 0);
return getEncodedAndThen(this::encrypt, ctrKey, macKey, plaintext, associatedData);
} catch (UnauthenticCiphertextException | IllegalBlockSizeException e) {
throw new IllegalStateException("Exceptions only expected during decryption", e);
}
}

Expand Down Expand Up @@ -188,23 +170,7 @@ public byte[] encrypt(byte[] ctrKey, byte[] macKey, byte[] plaintext, byte[]...
* @throws IllegalBlockSizeException If the provided ciphertext is of invalid length.
*/
public byte[] decrypt(SecretKey key, byte[] ciphertext, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException {
final byte[] keyBytes = key.getEncoded();
if (keyBytes.length != 64 && keyBytes.length != 48 && keyBytes.length != 32) {
throw new IllegalArgumentException("Key length must be 256, 384, or 512 bits.");
}
final int subkeyLen = keyBytes.length / 2;
assert subkeyLen == 32 || subkeyLen == 24 || subkeyLen == 16;
final byte[] macKey = new byte[subkeyLen];
final byte[] ctrKey = new byte[subkeyLen];
try {
System.arraycopy(keyBytes, 0, macKey, 0, macKey.length); // K1 = leftmost(K, len(K)/2);
System.arraycopy(keyBytes, macKey.length, ctrKey, 0, ctrKey.length); // K2 = rightmost(K, len(K)/2);
return decrypt(ctrKey, macKey, ciphertext, associatedData);
} finally {
Arrays.fill(macKey, (byte) 0);
Arrays.fill(ctrKey, (byte) 0);
Arrays.fill(keyBytes, (byte) 0);
}
return deriveSubkeysAndThen(this::decrypt, key, ciphertext, associatedData);
}

/**
Expand All @@ -220,17 +186,7 @@ public byte[] decrypt(SecretKey key, byte[] ciphertext, byte[]... associatedData
* @throws IllegalBlockSizeException If the provided ciphertext is of invalid length.
*/
public byte[] decrypt(SecretKey ctrKey, SecretKey macKey, byte[] ciphertext, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException {
final byte[] ctrKeyBytes = ctrKey.getEncoded();
final byte[] macKeyBytes = macKey.getEncoded();
if (ctrKeyBytes == null || macKeyBytes == null) {
throw new IllegalArgumentException("Can't get bytes of given key.");
}
try {
return decrypt(ctrKeyBytes, macKeyBytes, ciphertext, associatedData);
} finally {
Arrays.fill(ctrKeyBytes, (byte) 0);
Arrays.fill(macKeyBytes, (byte) 0);
}
return getEncodedAndThen(this::decrypt, ctrKey, macKey, ciphertext, associatedData);
}

/**
Expand Down Expand Up @@ -269,6 +225,70 @@ public byte[] decrypt(byte[] ctrKey, byte[] macKey, byte[] ciphertext, byte[]...
}
}


/**
* Either {@link #encrypt(byte[], byte[], byte[], byte[]...)} or {@link #decrypt(byte[], byte[], byte[], byte[]...)}.
*/
@FunctionalInterface
private interface EncryptOrDecrypt {
byte[] compute(byte[] ctrKey, byte[] macKey, byte[] ciphertext, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException;
}

/**
* Splits the key into two subkeys and then encrypts or decrypts the data.
* @param encryptOrDecrypt Either {@link #encrypt(byte[], byte[], byte[], byte[]...)} or {@link #decrypt(byte[], byte[], byte[], byte[]...)}
* @param key The combined key, with the leftmost half being the S2V key and the rightmost half being the CTR key
* @param data The to-be-encrypted plaintext or the to-be-decrypted ciphertext
* @param associatedData Optional associated data
* @return result of the encryptOrDecrypt function
* @throws UnauthenticCiphertextException If the authentication failed, e.g. because ciphertext and/or associatedData are corrupted (only during decryption).
* @throws IllegalBlockSizeException If the provided ciphertext is of invalid length (only during decryption).
*/
private byte[] deriveSubkeysAndThen(EncryptOrDecrypt encryptOrDecrypt, SecretKey key, byte[] data, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException {
final byte[] keyBytes = key.getEncoded();
if (keyBytes.length != 64 && keyBytes.length != 48 && keyBytes.length != 32) {
throw new IllegalArgumentException("Key length must be 256, 384, or 512 bits.");
}
final int subkeyLen = keyBytes.length / 2;
assert subkeyLen == 32 || subkeyLen == 24 || subkeyLen == 16;
final byte[] macKey = new byte[subkeyLen];
final byte[] ctrKey = new byte[subkeyLen];
try {
System.arraycopy(keyBytes, 0, macKey, 0, macKey.length); // K1 = leftmost(K, len(K)/2);
System.arraycopy(keyBytes, macKey.length, ctrKey, 0, ctrKey.length); // K2 = rightmost(K, len(K)/2);
return encryptOrDecrypt.compute(ctrKey, macKey, data, associatedData);
} finally {
Arrays.fill(macKey, (byte) 0);
Arrays.fill(ctrKey, (byte) 0);
Arrays.fill(keyBytes, (byte) 0);
}
}

/**
* Encrypts or decrypts data using the given keys.
* @param encryptOrDecrypt Either {@link #encrypt(byte[], byte[], byte[], byte[]...)} or {@link #decrypt(byte[], byte[], byte[], byte[]...)}
* @param ctrKey The part of the key used for the CTR computation
* @param macKey The part of the key used for the S2V computation
* @param data The to-be-encrypted plaintext or the to-be-decrypted ciphertext
* @param associatedData Optional associated data
* @return result of the encryptOrDecrypt function
* @throws UnauthenticCiphertextException If the authentication failed, e.g. because ciphertext and/or associatedData are corrupted (only during decryption).
* @throws IllegalBlockSizeException If the provided ciphertext is of invalid length (only during decryption).
*/
private byte[] getEncodedAndThen(EncryptOrDecrypt encryptOrDecrypt, SecretKey ctrKey, SecretKey macKey, byte[] data, byte[]... associatedData) throws UnauthenticCiphertextException, IllegalBlockSizeException {
final byte[] ctrKeyBytes = ctrKey.getEncoded();
final byte[] macKeyBytes = macKey.getEncoded();
if (ctrKeyBytes == null || macKeyBytes == null) {
throw new IllegalArgumentException("Can't get bytes of given key.");
}
try {
return encryptOrDecrypt.compute(ctrKeyBytes, macKeyBytes, data, associatedData);
} finally {
Arrays.fill(ctrKeyBytes, (byte) 0);
Arrays.fill(macKeyBytes, (byte) 0);
}
}

@VisibleForTesting
byte[] computeCtr(byte[] input, byte[] key, final byte[] iv) {
// clear out the 31st and 63rd (rightmost) bit:
Expand Down

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