Security risks associated with data padding

Data padding in encryption is a method of adding extra bits to the input to ensure that it meets the encryption algorithm standard input block size. Let’s first discuss the fixed-size encryption algorithm to understand the concept better.

Encryption input fixed block size

The block size of the text to be encrypted is fixed size, which means the input block data size must equal the block size of the encryption algorithm. If the length of the input is larger than the block size, it divides the input into multiple blocks. However, data padding is done if the size is less than the block size. Data padding adds extra data to the input to equal the multiple of block size.

There are many padding algorithms to do that, but each has drawbacks. The standard padding algorithms include zero padding, PKCS#7 padding, and bit padding. All these algorithms work by adding an extra character or a set of characters at the end of the text block, which means any data can replace it. The padding can be used to trick the algorithm into leaking information, retrieve parts of texts, or could be used to reveal the key involved.

Later in this Answer, we’ll discuss how security is compromised due to data padding.

Padding oracle attacks

Padding oracle schemes work by targeting the weaknesses in the padding schemes of the encryption algorithms. Once the attacker identifies the weakness, it targets the system by sending differently crafted cipher text for decryption each time to get the response. If the padding is correct, the attacker can get the 200 code. Otherwise, there might be an error. The attacker analyzes the error like invalid padding, incorrect length, etc. After a series of tests, the attacker analyzes the behavior and concludes whether the padding is right or wrong. The illustration below shows the brute force attack in failure and success scenarios.

The process continues iteratively until all blocks of ciphertext are successfully decrypted. In each iteration, the attacker modifies the ciphertext a little to identify the changes in response. In the end, the attacker retrieves the plaintext. This is a hazard because the attacker can get the plaintext without knowing the secret key. Sometimes, the attacker might be smart enough to retrieve the encryption key.

Timing attacks

Some encryption algorithms use input sanitizationThe process of validating the contents of input and removing malicious codes. and padding validationThe technique used by encryption algorithms to ensure that the padding follows the standard. techniques. So, the attacker opts for techniques such as manipulating the time difference between verification and decryption. The attacker uses side-channel attacks to reveal the time taken by the process to execute.

The encryption and decryption process time changes with the type of algorithm used. The attacker generates different input data and calculates the time taken to process each input data. Multiple inputs and specific execution times against the input data can reveal different patterns. The attacker’s capability to guess the valid and invalid padding points can be used to reveal the processed information. If the process is continued, the attacker, by identifying the pattern, can disclose the sensitive information and the respective key used.

Scheme and algorithm interoperability

Each block-based encryption algorithm uses a specified padding algorithm. If the padding scheme is inoperable with the encryption algorithm, it may cause faulty outputs and weaken its ability to detect unsanitized padding. An attacker can exploit this system vulnerability and use it to retrieve the original text and associated encryption key.

Weak encryption algorithm

The strength of the ciphertext lies in the secret key and type of algorithm used. If the attacker can successfully determine the algorithm used, they can use this information against the user. The key size determines the strength of the algorithm. For older algorithms, the encryption keys are small and, hence, easier to break by brute force. Weak encryption algorithms, besides using strong padding schemes, are a security hazard because the ciphertext is easily decryptable once the key is retrieved.

Increased attack surface

The data padding increases the attack surface of the user’s system by giving characters and bits for the attacker to manipulate for its benefit. Increased attack surface leads to many other types of attacks. Here are some common attacks the attacker can do after exploiting the vulnerabilities caused by padding.

Safe practices

There are some security standards to ensure that confidential information remains secure. To establish a secure connection, we must use encrypted channels to communicate. To enhance security, these are some essential steps you should follow:

1. Use industry-standard up-to-date encryption algorithms.

2. Ensure the interoperability of the padding scheme and encryption algorithm.

3. Sanitize the input entering the algorithms.

4. Use noncesA value used in conjuction with a key to ensure that multiple encryption produces differnt ciphertexts. The nonce is only used one time. to further increase the strength of keys.

5. Run security audits on your system.

Quiz

Take a quick quiz to see how well you comprehend security risks associated with data padding.

Conclusion

We’ve discussed how the fixed-sized encryption algorithm works and how padding ensures that the input to the encryption algorithm is accurate. We’ve also explored the security drawbacks of using the padding technique.