CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks

What is Comparison Logic is Vulnerable to Power Side-Channel Attacks?

• Overview: Comparison logic vulnerable to power side-channel attacks is a vulnerability where attackers can monitor the power consumption of a device during the evaluation of security tokens. This information can be used to deduce the value of the reference token if the comparison logic is not implemented securely.

• Exploitation Methods:

• Attackers can exploit this by monitoring real-time power consumption variations during token evaluations.
• Common techniques include using power analysis attacks to differentiate between "good" and "bad" token entries based on power usage patterns.

• Security Impact:

• Direct consequences include unauthorized access due to deduced security tokens.
• Potential cascading effects involve further data breaches if attackers gain access to sensitive systems or information.
• Business impact could be severe, including loss of customer trust, financial losses, and legal implications.

• Prevention Guidelines:

• Implement constant-time comparison algorithms to prevent power variations during token evaluation.
• Limit the number of retries for token entry to reduce attack feasibility.
• Employ power analysis-resistant hardware and software solutions.
• Use cryptographic libraries designed to mitigate side-channel attacks.
• Regularly audit and test systems for side-channel vulnerabilities using specialized tools.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

```python secure_compare.py {1-7}
def insecure_compare(secret, user_input):
    # Vulnerable comparison logic: this checks each character sequentially
    # and exits early if a mismatch is found.
    for x, y in zip(secret, user_input):
        if x != y:
            return False
    # Additionally checks if both strings are of the same length
    return len(secret) == len(user_input)

# Example usage
secret_token = "SuperSecretToken123"
user_input = "UserInputToken456"
print(insecure_compare(secret_token, user_input))

Explanation of the Vulnerability

• Vulnerability: The insecure_compare function performs a character-by-character comparison of secret and user_input. If a mismatch is found, the function exits early. This behavior allows an attacker to perform a power side-channel attack by measuring the time taken or power consumed to deduce the number of matching characters, providing clues about the secret.

How to fix Comparison Logic is Vulnerable to Power Side-Channel Attacks?

Fixed Code Example

import hmac

def secure_compare(secret, user_input):
    # Fixed comparison logic: use hmac.compare_digest for constant-time comparison
    return hmac.compare_digest(secret, user_input)

# Example usage
secret_token = "SuperSecretToken123"
user_input = "UserInputToken456"
print(secure_compare(secret_token, user_input))

Explanation of the Fix

• Fix: The hmac.compare_digest function is used for comparing secret and user_input. It performs the comparison in constant time, ensuring that the execution time is not dependent on the number of matching characters. This mitigates the risk of timing and power side-channel attacks.
• Best Practice: Use cryptographic libraries that provide constant-time operations when comparing sensitive data to prevent side-channel attacks.