COMMON WEAKNESS ENUMERATIONDraft

CWE-1255

Comparison Logic is Vulnerable to Power Side-Channel Attacks

A device's real time power consumption may be monitored during security token evaluation and the information gleaned may be used to determine the value of the reference token.

Abstraction

Variant

Structure

Simple

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

A device's real time power consumption may be monitored during security token evaluation and the information gleaned may be used to determine the value of the reference token.

Extended description

The power consumed by a device may be instrumented and monitored in real time. If the algorithm for evaluating security tokens is not sufficiently robust, the power consumption may vary by token entry comparison against the reference value. Further, if retries are unlimited, the power difference between a "good" entry and a "bad" entry may be observed and used to determine whether each entry itself is correct thereby allowing unauthorized parties to calculate the reference value.

Root cause

How and when does the problem arise?

Lifecycle phase

Architecture and Design

The design of the algorithm itself may intrinsically allow the power side channel attack to be effective.

Lifecycle phase

Implementation

This weakness may be introduced during implementation despite a robust design that otherwise prevents exploitation.

Risk

What does successful exploitation lead to?

Modify MemoryRead MemoryRead Files or DirectoriesModify Files or DirectoriesExecute Unauthorized Code or CommandsGain Privileges or Assume IdentityBypass Protection MechanismRead Application DataModify Application DataHide Activities

Affected security scopes: Confidentiality, Integrity, Availability, Access Control, Accountability, Authentication, Authorization, Non-Repudiation

As compromising a security token may result in complete system control, the impacts are relatively universal.

Defence

How is it prevented and fixed?

Architecture and Design

Architecture and design approach

Detail
The design phase must consider each check of a security token against a standard and the amount of power consumed during the check of a good token versus a bad token. The alternative is an all at once check where a retry counter is incremented PRIOR to the check.

Architecture and Design

Architecture and design approach

Detail
Another potential mitigation is to parallelize shifting of secret data (see example 2 below). Note that the wider the bus the more effective the result.

Architecture and Design

Architecture and design approach

Detail
An additional potential mitigation is to add random data to each crypto operation then subtract it out afterwards. This is highly effective but costly in performance, area, and power consumption. It also requires a random number generator.

Implementation

Implementation-phase defence

Detail
If the architecture is unable to prevent the attack, using filtering components may reduce the ability to implement an attack, however, consideration must be given to the physical removal of the filter elements.

Integration

Integration aşaması savunması

Detail
During integration, avoid use of a single secret for an extended period (e.g. frequent key updates). This limits the amount of data compromised but at the cost of complexity of use.