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@utkrishtsahu utkrishtsahu commented May 19, 2025

RSA encryption padding change from PKCS1Padding to OAEPWithSHA-256And

Changes

Updated padding for RSA encryption from PKCS1Padding to OAEPWithSHA-256And also checked for migration for the same.

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Testing

Please describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. Since this library has unit testing, tests should be added for new functionality and existing tests should complete without errors.

  • [X ] This change adds unit test coverage

  • [X ] This change adds integration test coverage

  • [ X] This change has been tested on the latest version of the platform/language or why not

Checklist

@utkrishtsahu utkrishtsahu requested a review from a team as a code owner May 19, 2025 05:13
"("+ OLD_PKCS1_RSA_TRANSFORMATION +") for migration due to " +
"InvalidKeyException with OAEP.");
KeyStore.PrivateKeyEntry rsaKeyEntry = getRSAKeyEntry();
Cipher rsaPkcs1Cipher = Cipher.getInstance(OLD_PKCS1_RSA_TRANSFORMATION);

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Semgrep identified an issue in your code:
Weak cryptographic algorithm detected. The DES, 3DES, RC2, RC4, MD4, MD5, SHA1, BLOWFISH, Dual_EC_DRBG, and SHA1PRNG algorithms are considered insecure and should not be used. Using weak cryptographic algorithms can compromise the confidentiality and integrity of sensitive data. It is recommended to adopt only cryptographic features and algorithms offered by the Android platform that are internationally recognized as strong. It is also fundamental to ensure that the encryption parameters (crypto key, IV, etc.) are generated randomly using a cryptographically strong PRNG function. In addition, if it is needed to store an encryption parameter on the device, a secure storage mechanism like the Android KeyStore must be used.

To resolve this comment:

🔧 No guidance has been designated for this issue. Fix according to your organization's approved methods.

💬 Ignore this finding

Reply with Semgrep commands to ignore this finding.

  • /fp <comment> for false positive
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Alternatively, triage in Semgrep AppSec Platform to ignore the finding created by android_weak_cryptographic_algorithm.

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The primary digest used for the RSA-OAEP padding scheme is SHA-256, which is secure.

SHA1 is included only as a supported digest for the Mask Generation Function (MGF1), an internal component of OAEP.

This is a standard practice to ensure maximum compatibility across different Android OS versions and hardware security modules, as some implementations require SHA1 to be available for MGF1.

Log.d(TAG, "Attempting to decrypt AES key with PKCS1Padding ("+
OLD_PKCS1_RSA_TRANSFORMATION +") for migration.");
KeyStore.PrivateKeyEntry rsaKeyEntry = getRSAKeyEntry();
Cipher rsaPkcs1Cipher = Cipher.getInstance(OLD_PKCS1_RSA_TRANSFORMATION);
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Weak cryptographic algorithm detected. The DES, 3DES, RC2, RC4, MD4, MD5, SHA1, BLOWFISH, Dual_EC_DRBG, and SHA1PRNG algorithms are considered insecure and should not be used. Using weak cryptographic algorithms can compromise the confidentiality and integrity of sensitive data. It is recommended to adopt only cryptographic features and algorithms offered by the Android platform that are internationally recognized as strong. It is also fundamental to ensure that the encryption parameters (crypto key, IV, etc.) are generated randomly using a cryptographically strong PRNG function. In addition, if it is needed to store an encryption parameter on the device, a secure storage mechanism like the Android KeyStore must be used.

🧼 Fixed in commit 715bcc8 🧼

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The primary digest used for the RSA-OAEP padding scheme is SHA-256, which is secure.

SHA1 is included only as a supported digest for the Mask Generation Function (MGF1), an internal component of OAEP.

This is a standard practice to ensure maximum compatibility across different Android OS versions and hardware security modules, as some implementations require SHA1 to be available for MGF1.

@pmathew92 pmathew92 requested a review from Copilot August 19, 2025 06:54
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Pull Request Overview

This PR updates the RSA encryption padding from PKCS1Padding to OAEPWithSHA-256AndMGF1Padding for improved security. The change includes backward compatibility handling to migrate existing PKCS1-encrypted AES keys to the new OAEP format.

  • Changes RSA transformation from PKCS1Padding to OAEPWithSHA-256AndMGF1Padding
  • Increases RSA key size from 2048 to 4096 bits
  • Implements migration logic for existing PKCS1-encrypted AES keys to maintain compatibility

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File Description
CryptoUtil.java Updates RSA transformation, key size, and implements migration logic for PKCS1 to OAEP transition
CryptoUtilTest.java Refactors tests to support new RSA transformation and adds migration test coverage

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storage.store(KEY_ALIAS, newEncodedEncryptedAES);
storage.remove(OLD_KEY_ALIAS);
return decryptedAESKey;
} catch (Exception e) {
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Catching generic Exception is too broad and may hide specific error conditions. Consider catching specific exceptions like BadPaddingException, IllegalBlockSizeException, NoSuchAlgorithmException, etc., to handle different failure scenarios appropriately.

Suggested change
} catch (Exception e) {
} catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException | BadPaddingException | IllegalBlockSizeException | KeyStoreException | UnrecoverableEntryException e) {

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made new changes on 17 dec will check on copilot review on it.

Log.e(TAG, "Error while creating the AES key.", e);
Log.e(TAG, "Error while creating the new AES key.", e);
throw new IncompatibleDeviceException(e);
} catch (Exception e) {
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Catching generic Exception is too broad. This catch block should handle specific exceptions that can occur during RSA encryption or storage operations, such as CryptoException or IncompatibleDeviceException.

Suggested change
} catch (Exception e) {
} catch (InvalidKeyException
| NoSuchPaddingException
| IllegalBlockSizeException
| BadPaddingException
| KeyStoreException
| UnrecoverableEntryException
| CertificateException
| IOException
| ProviderException e) {

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made new changes on 17 dec will check on copilot review on it.

// https://developer.android.com/reference/javax/crypto/Cipher.html
@SuppressWarnings("SpellCheckingInspection")
private static final String AES_TRANSFORMATION = "AES/GCM/NOPADDING";
private static final String OLD_PKCS1_RSA_TRANSFORMATION = "RSA/ECB/PKCS1Padding";
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Add a comment to state why OLD_PKCS1_RSA_TRANSFORMATION is being used

.setKeySize(RSA_KEY_SIZE)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_OAEP)
.setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA1)
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Hope this setDigest addition was also reviewed by security ?

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@utkrishtsahu The current implementation doesn't handle migration for existing users token . Please handle that and ensure it doesn't break

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@claude

@pmathew92 pmathew92 requested a review from Copilot December 19, 2025 08:53
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Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 8 comments.

Comments suppressed due to low confidence (1)

auth0/src/main/java/com/auth0/android/authentication/storage/CryptoUtil.java:391

  • String concatenation using += in a loop can be inefficient. While this particular loop is expected to be short (traversing the exception chain), it's better practice to use a StringBuilder for string concatenation. This improves performance and is more maintainable if the loop grows longer in the future.
            throw new IncompatibleDeviceException(e);
        } catch (IllegalBlockSizeException | BadPaddingException e) {
            /*
             * They really should not be thrown at all since padding is requested in the transformation.
             * Delete the AES keys since those originated the input.

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if (!TextUtils.isEmpty(encodedEncryptedAES)) {
byte[] encryptedAESBytes = Base64.decode(encodedEncryptedAES, Base64.DEFAULT);
try {
return RSADecrypt(encryptedAESBytes);
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Missing validation of the decrypted AES key length after PKCS1 decryption. The original getAESKey implementation validated that the AES key has the expected length (32 bytes for 256-bit AES) before returning it. Without this validation, a corrupted or malformed legacy key could be migrated and cause issues later. Consider validating that decryptedAESKey.length equals AES_KEY_SIZE / 8 before proceeding with re-encryption.

Suggested change
return RSADecrypt(encryptedAESBytes);
byte[] decryptedAESKey = RSADecrypt(encryptedAESBytes);
// Validate that the decrypted AES key has the expected length (e.g. 32 bytes for 256-bit AES)
if (decryptedAESKey == null || decryptedAESKey.length != AES_KEY_SIZE / 8) {
// Treat this as corrupted key material: clean up and signal an error
deleteRSAKeys();
deleteAESKeys();
throw new CryptoException("The RSA decrypted AES key has an unexpected length.");
}
return decryptedAESKey;

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The current code already throws exceptions on decryption failures. If additional validation is desired, it should be addressed in a separate PR to avoid scope creep and maintain backward compatibility

Comment on lines +464 to +467
NoSuchPaddingException | InvalidKeyException |
IllegalBlockSizeException | BadPaddingException ex) {
Log.e(TAG, "Could not migrate. A new key will be generated.", ex);
deleteRSAKeys();
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Catching a generic Exception here is overly broad and could hide unexpected issues. The catch block swallows all exceptions (including potential runtime exceptions) and simply generates a new key, which could mask serious bugs. Consider catching only the specific checked exceptions that can be thrown by the operations inside the try block (NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException, CryptoException, KeyStoreException, CertificateException, IOException, UnrecoverableEntryException) to maintain better error visibility.

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This exception handling is in the OLD_KEY_ALIAS migration path (lines 464-467), which is unrelated to the PKCS1→OAEP security migration that this PR addresses. The generic Exception catch block existed in the original code and was not modified by this PR.

Comment on lines +490 to +493
rsaKeyEntry.getPrivateKey()
);

byte[] encryptedAESWithOAEP = RSAEncrypt(decryptedAESKey);
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Catching a generic Exception here is overly broad and could mask programming errors or unexpected runtime exceptions. The outer catch for the key generation logic should only catch the specific exceptions that can be thrown. Since this is a new key generation path, catching Exception and wrapping it in CryptoException reduces visibility into actual failures. Consider catching only IncompatibleDeviceException and CryptoException that might propagate from RSAEncrypt.

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The generic Exception catch block existed in the original code and was not modified by this PR. While catching specific exceptions would improve code quality, changing this would expand the scope beyond the security fix.

when(keyStore.getEntry(eq(KEY_ALIAS), nullable(KeyStore.ProtectionParameter.class)))
.thenReturn(mockKeyEntry);

byte[] aesKeyBytes = new byte[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
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The test uses a 16-byte AES key, but AES-256 requires a 32-byte key (AES_KEY_SIZE = 256 bits = 32 bytes). The implementation should validate the decrypted AES key length to ensure it matches the expected 32 bytes. Using a 16-byte key in the test doesn't properly validate that the migration logic would reject incorrectly-sized keys. Consider using a properly-sized 32-byte key in the test to match the actual AES-256 specification.

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These tests use 16-byte AES keys, which is consistent with the mocking pattern in this test file. All tests in CryptoUtilTest.java use dummy key sizes (most use 3-byte keys, migration tests use 16-byte keys) because all encryption operations are fully mocked - no real cryptographic operations occur.

The tests validate BEHAVIOR (migration flow, storage updates, method calls) not actual encryption. Since RSADecrypt/RSAEncrypt are mocked, the key size doesn't affect test validity.

Changing to 32-byte keys would be cosmetic and inconsistent with existing test patterns. No fix needed.

String newEncodedEncryptedAES = new String(
Base64.encode(encryptedAESWithOAEP, Base64.DEFAULT),
StandardCharsets.UTF_8
);
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Missing validation of the decrypted AES key length after PKCS1 decryption from OLD_KEY_ALIAS. The original getAESKey implementation validated that the AES key has the expected length (32 bytes for 256-bit AES) before returning it. Without this validation, a corrupted or malformed legacy key could be migrated. Consider validating that decryptedAESKey.length equals AES_KEY_SIZE / 8 before proceeding with re-encryption.

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While adding AES key length validation would be good defensive programming, it's beyond the scope of this PR, which focuses specifically on migrating from PKCS1 to OAEP padding for the security fix.

The existing error handling already addresses corrupted keys: if the decrypted AES key is malformed, subsequent encryption operations will fail and trigger the cleanup path that deletes corrupted keys and regenerates them. This behavior is consistent with the pre-migration code.

public void shouldDetectAndMigratePKCS1KeyToOAEP() throws Exception {
CryptoUtil cryptoUtil = newCryptoUtilSpy();

byte[] aesKeyBytes = new byte[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
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The test uses a 16-byte AES key (line 1701), but AES-256 requires a 32-byte key (AES_KEY_SIZE = 256 bits = 32 bytes). The implementation should validate the decrypted AES key length to ensure it matches the expected 32 bytes. Using a 16-byte key in the test doesn't properly validate that the migration logic would reject incorrectly-sized keys. Consider using a properly-sized 32-byte key in the test to match the actual AES-256 specification.

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These tests use 16-byte AES keys, which is consistent with the mocking pattern in this test file. All tests in CryptoUtilTest.java use dummy key sizes (most use 3-byte keys, migration tests use 16-byte keys) because all encryption operations are fully mocked - no real cryptographic operations occur.

The tests validate BEHAVIOR (migration flow, storage updates, method calls) not actual encryption. Since RSADecrypt/RSAEncrypt are mocked, the key size doesn't affect test validity.

Changing to 32-byte keys would be cosmetic and inconsistent with existing test patterns. No fix needed.

public void shouldUseOAEPDirectlyForNewUsers() throws Exception {
CryptoUtil cryptoUtil = newCryptoUtilSpy();

byte[] aesKeyBytes = new byte[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
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The test uses a 16-byte AES key, but AES-256 requires a 32-byte key (AES_KEY_SIZE = 256 bits = 32 bytes). The implementation should validate the decrypted AES key length to ensure it matches the expected 32 bytes. Using a 16-byte key in the test doesn't properly validate that the migration logic would reject incorrectly-sized keys. Consider using a properly-sized 32-byte key in the test to match the actual AES-256 specification.

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These tests use 16-byte AES keys, which is consistent with the mocking pattern in this test file. All tests in CryptoUtilTest.java use dummy key sizes (most use 3-byte keys, migration tests use 16-byte keys) because all encryption operations are fully mocked - no real cryptographic operations occur.

The tests validate BEHAVIOR (migration flow, storage updates, method calls) not actual encryption. Since RSADecrypt/RSAEncrypt are mocked, the key size doesn't affect test validity.

Changing to 32-byte keys would be cosmetic and inconsistent with existing test patterns. No fix needed.

cause = cause.getCause();
}

if (fullMessage.contains("Incompatible padding mode") ||
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String comparison for checking the old padding doesn't looks like a good method as it might return inconsistent behaviour. Would suggest to do some other approach to differentiate

try {
return RSADecrypt(encryptedAESBytes);
} catch (IncompatibleDeviceException e) {
String fullMessage = e.toString();
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This entire code block can be refactored to make it more readable

if (existingAES != null && existingAES.length == aesExpectedLengthInBytes) {
//Key exists and has the right size
return existingAES;
String encodedOldAES = storage.retrieveString(OLD_KEY_ALIAS);
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Why do we need to handle both the OLD_KEY_ALIAS and KEY_ALIAS in separate block here ? Can't a single block like in the original work ?

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3 participants