Description
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.
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.
Potential Impact
Confidentiality, Integrity, Availability, Access Control, Accountability, Authentication, Authorization, Non-Repudiation
Modify Memory, 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
Demonstrative Examples
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--;
while (true)
// Password OKstatic nonvolatile password_tries = NUM_RETRIES;
do
while (password_tries == 0) ; // Hang here if no more password tries
password_tries--; // Put retry code here to catch partial retries
password_ok = 0;
for (i = 0; i < NUM_PW_DIGITS; i++)
if (GetPasswordByte() == stored_password([i])
password_ok |= 0x10; // Power consumption here
else
password_ok |= 0x01; // is now the same here
end
if ((password_ok & 1) == 0)
password_tries = NUM_RETRIES;
break_to_Ok_to_proceed
while (true)
// Password OKmodule siso(clk,rst,a,q);
input a;
input clk,rst;
output q;
reg q;
always@(posedge clk,posedge rst)
begin
if(rst==1'b1)
q<1'b0;
else
q<a;
end
endmodulemodule pipo(clk,rst,a,q);
input clk,rst;
input[3:0]a;
output[3:0]q;
reg[3:0]q;
always@(posedge clk,posedge rst)
begin
if (rst==1'b1)
q<4'b0000;
else
q<a;
end
endmoduleMitigations & Prevention
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.
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.
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.
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.
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.
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2020-12788 | CMAC verification vulnerable to timing and power attacks. |
Related Weaknesses
Frequently Asked Questions
What is CWE-1255?
CWE-1255 (Comparison Logic is Vulnerable to Power Side-Channel Attacks) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. 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.
How can CWE-1255 be exploited?
Attackers can exploit CWE-1255 (Comparison Logic is Vulnerable to Power Side-Channel Attacks) to modify memory, 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. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.
How do I prevent CWE-1255?
Key mitigations include: 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
What is the severity of CWE-1255?
CWE-1255 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 1 real-world CVEs.