CWE-1300: Improper Protection of Physical Side Channels | Glexia

Causes

• Consider a device that checks a passcode to unlock the screen. PIN numbers used to unlock a cell phone should not exhibit any characteristics about themselves. This creates a side channel. An attacker could monitor the pulses using an oscilloscope or other method. Once the first character is correctly guessed (based on the oscilloscope readings), they can then move to the next character, which is much more efficient than the brute force method of guessing every possible sequence of characters.
• Consider the device vulnerability CVE-2021-3011, which affects certain microcontrollers [REF-1221]. The Google Titan Security Key is used for two-factor authentication using cryptographic algorithms. The device uses an internal secret key for this purpose and exchanges information based on this key for the authentication. If this internal secret key and the encryption algorithm were known to an adversary, the key function could be duplicated, allowing the adversary to masquerade as the legitimate user.
• The code snippet provided here is part of the modular exponentiation module found in the HACK@DAC'21 Openpiton System-on-Chip (SoC), specifically within the RSA peripheral [REF-1368]. Modular exponentiation, denoted as "a^b mod n," is a crucial operation in the RSA public/private key encryption. In RSA encryption, where 'c' represents ciphertext, 'm' stands for a message, and 'd' corresponds to the private key, the decryption process is carried out using this modular exponentiation as follows: m = c^d mod n, where 'n' is the result of multiplying two large prime numbers. The vulnerable code shows a buggy implementation of binary exponentiation where it updates the result register (result_reg) only when the corresponding exponent bit (exponent_reg[0]) is set to 1. However, when this exponent bit is 0, the output register is not updated. It's important to note that this implementation introduces a physical power side-channel vulnerability within the RSA core. This vulnerability could expose the private exponent to a determined physical attacker. Such exposure of the private exponent could lead to a complete compromise of the private key.,To address mitigation requirements, the developer can develop the module by minimizing dependency on conditions, particularly those reliant on secret keys. In situations where branching is unavoidable, developers can implement masking mechanisms to obfuscate the power consumption patterns exhibited by the module (see good code example). Additionally, certain algorithms, such as the Karatsuba algorithm, can be implemented as illustrative examples of side-channel resistant algorithms, as they necessitate only a limited number of branch conditions [REF-1369].

Remediation

• Architecture and Design: Apply blinding or masking techniques to implementations of cryptographic algorithms.
• Implementation: Add shielding or tamper-resistant protections to the device to increase the difficulty of obtaining measurements of the side-channel.

Detection

• Manual Analysis: Perform a set of leakage detection tests such as the procedure outlined in the Test Vector Leakage Assessment (TVLA) test requirements for AES [REF-1230]. TVLA is the basis for the ISO standard 17825 [REF-1229]. A separate methodology is provided by [REF-1228]. Note that sole reliance on this method might not yield expected results [REF-1239] [REF-1240].
• Manual Analysis:

Related CWEs

• CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks
• CWE-203: Observable Discrepancy
• CWE-203: Observable Discrepancy

Related CVEs

Related CVE mappings appear after CVE records are cross-indexed.

ATT&CK Relevance

ATT&CK relevance is shown only when reviewed or responsibly inferred.