Question

In an OTA update process, what is the function of a digital signature when verifying a new firmware image before execution?

Accepted Answer

In an Over-the-Air (OTA) update, a digital signature acts as a cryptographic seal that guarantees the authenticity and integrity of the firmware image before it is installed. Authenticity confirms that the update originated from a trusted source, such as the device manufacturer, rather than an attacker. Integrity ensures that the firmware has not been modified, corrupted, or tampered with during transit from the server to the device. The process begins when the manufacturer creates a unique hash of the firmware, which is a fixed-length string of characters representing the exact data within the file. The manufacturer then encrypts this hash using their private key to create the digital signature. When the device receives the update, it uses the manufacturer&#x27;s corresponding public key—which is securely stored on the device—to decrypt the signature and recover the original hash. Simultaneously, the device independently calculates a new hash of the received firmware file. The device then compares the decrypted hash from the signature with the newly calculated hash. If the two hashes match exactly, the device confirms the firmware is genuine and untampered, allowing it to proceed with the execution. If the hashes do not match, the device rejects the update because the firmware may be malicious or incomplete, preventing potential security breaches or device failure.

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In an OTA update process, what is the function of a digital signature when verifying a new firmware image before execution?