2063
Scope Impact Likelihood
Integrity
Availability
Access Control
Accountability
Authentication
Authorization
Non-Repudiation
Read Memory
Read Files or Directories
Modify Files or Directories
Execute Unauthorized Code or Commands
Gain Privileges or Assume Identity
Bypass Protection Mechanism
Read Application Data
Modify Application Data
Hide Activities
As compromising a security token may result in complete
system control, the impacts are relatively universal
Potential Mitigations
Phase: Architecture and Design
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.
Phase: Architecture and Design
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.
Phase: Architecture and Design
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.
Phase: Implementation
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.
Phase: Integration
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.
Demonstrative Examples
Example 1:
Consider an example hardware module that checks a user-provided password (or PIN) to grant
access to a user. The user-provided password is compared against a stored value byte-by-byte.
Example Language: C (Bad)
static nonvolatile password_tries = NUM_RETRIES;
do
while (password_tries == 0) ; // Hang here if no more password tries
password_ok = 0;
for (i = 0; i < NUM_PW_DIGITS; i++)
if (GetPasswordByte() == stored_password([i])
password_ok |= 1; // Power consumption is different here
else
password_ok |= 0; // than from here
end
if (password_ok > 0)
password_tries = NUM_RETRIES;
break_to_Ok_to_proceed
password_tries--;
CWE Version 4.14
CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks
CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks