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In automotive cybersecurity, many encryption and signature verification algorithms are often used. Today, we will discuss the principles of encryption algorithms and their implementations, which can help in understanding encryption algorithms and ensuring the correctness of their implementation.

01

Application Scenarios of Encryption Algorithms and Signature Verification in Automotive Cybersecurity

1. Secure Boot

Ensuring the authenticity of the boot program, encryption algorithms are applied: The boot program of a vehicle (such as the Bootloader) is usually protected using encryption algorithms. A hash algorithm (such as SHA-256) can be used to compute a hash of the boot program, generating a fixed-length hash value. This hash value acts like a “fingerprint” of the boot program; any slight change in the content of the boot program will result in a completely different hash value. The hash value is then stored along with the boot program and encrypted using an encryption algorithm to prevent tampering.

Signature verification application: When the vehicle starts, the hardware first loads the boot program. During the loading process, the hash value of the boot program is decrypted, and the hash value of the boot program is recalculated and compared. Additionally, the signature of the hash value is verified to ensure its authenticity and integrity. This method prevents attackers from replacing or tampering with the boot program, ensuring that the vehicle starts from a trusted boot program.

2. Software Updates

Encryption algorithm application: Automotive manufacturers push software update packages to vehicles over the network. To prevent the update package from being tampered with or stolen during transmission, encryption algorithms are used to encrypt the update package. For example, the SHA-256 algorithm can be used to compute a hash of the update package, generating a unique hash value, which is sent along with the update package to the vehicle. Upon receiving the update package, the vehicle recalculates the hash value of the update package and compares it with the received hash value to ensure the integrity of the update package.

Signature verification application: When the vehicle receives a software update, it needs to verify the legitimacy of the update package’s source. Automotive manufacturers digitally sign the update package when releasing it, and the vehicle verifies the signature to confirm whether the update package was issued by a legitimate manufacturer, thus preventing malicious software from masquerading as an update package installed in the vehicle.

02

Working Principle of AES-CBC

1. Encryption Process

First, the plaintext is divided into fixed-length blocks, typically 128 bits in AES. For the first plaintext block, it is XORed with a randomly generated Initialization Vector (IV), and the result is encrypted using the AES key to obtain the first ciphertext block. Each subsequent plaintext block is XORed with the previous ciphertext block before being encrypted with the AES key, and so on. Thus, the generation of each ciphertext block depends not only on the current plaintext block and key but also on the previous ciphertext block, forming a chain structure, which is the origin of the CBC mode name.

2. Decryption Process

In contrast to the encryption process, the ciphertext block is first decrypted using the AES key, and then the decrypted result is XORed with the previous ciphertext block (for the first ciphertext block, it is XORed with the IV) to obtain the plaintext block. This process is repeated for each ciphertext block to ultimately restore the original plaintext.

3. Implementation Process

4. Implementation Results

03

Explanation and Implementation of AES-CMAC

AES-CMAC is an authenticated encryption mode based on the Advanced Encryption Standard (AES), which stands for Cipher-based Message Authentication Code.

1. Working Principle Process

2. Implementation Process

3. Implementation Results

Source:

https://blog.csdn.net/xiaoxinxinxinxin/article/details/147264716

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