89 byte[] encryptedBytes = new byte[encryptedSize];
90 System.arraycopy(encryptedIvTextBytes, ivSize, encryptedBytes, 0, encryptedSize);
91 SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
92 Cipher cipherDecrypt = Cipher.getInstance("AES/CBC/PKCS5Padding"); 93 cipherDecrypt.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
94 byte[] decrypted = cipherDecrypt.doFinal(encryptedBytes);
95 59 SecureRandom random = new SecureRandom();
60 random.nextBytes(iv);
61 IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
62 Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); 63 SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
64 cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec);
65 byte[] encrypted = cipher.doFinal(clean);The ciphertext produced is susceptible to alteration by an adversary. This means that the cipher provides no way to detect that the data has been tampered with. If the ciphertext can be controlled by an attacker, it could be altered without detection.
The solution is to use a cipher that includes a Hash-based Message Authentication Code (HMAC) to sign the data. Combining an HMAC function with the existing cipher is prone to error. Specifically, it is always recommended that you be able to verify the HMAC first, and only if the data is unmodified, do you then perform any cryptographic functions on the data. Essentially, it is best to provide an encrypted payload with the HMAC of the encrypted data which can be used to verify integrity before decryption.
The following modes are vulnerable because they don't provide an HMAC:
- CBC
- OFB
- CTR
- ECB
Bad Practice
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.ENCRYPT_MODE, k, iv);
byte[] cipherText = c.doFinal(plainText);
Recommended
Use a cipher mode that supports HMACs for verification by default, such as GCM:
Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
c.init(Cipher.ENCRYPT_MODE, k, iv);
byte[] cipherText = c.doFinal(plainText);
References
- FindSecBugs - CIPHER_INTEGRITY
- Moxie Marlinspike - The Cryptographic Doom Principle
- CWE-310 - Cryptographic Issues
- CWE-353 - Missing Support for Integrity Check
- OWASP Top Ten (2021) - Category A02 - Cryptographic Failures