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Home > CWE List > CWE-1431: Driving Intermediate Cryptographic State/Results to Hardware Module Outputs (4.18)  
ID

CWE-1431: Driving Intermediate Cryptographic State/Results to Hardware Module Outputs

Weakness ID: 1431
Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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+ Description
The product uses a hardware module implementing a cryptographic algorithm that writes sensitive information about the intermediate state or results of its cryptographic operations via one of its output wires (typically the output port containing the final result).
+ Common Consequences
Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Impact Details

Read Memory; Read Application Data

Scope: Confidentiality

Likelihood: Unknown

Mathematically sound cryptographic algorithms rely on their correct implementation for security. These assumptions might break when a hardware crypto module leaks intermediate encryption states or results such that they can be observed by an adversary. If intermediate state is observed, it might be possible for an attacker to identify the secrets used in the cryptographic operation.
+ Potential Mitigations
Phase(s) Mitigation

Architecture and Design

Designers/developers should add or modify existing control flow logic along any data flow paths that connect "sources" (signals with intermediate cryptographic state/results) with "sinks" (hardware module outputs and other signals outside of trusted cryptographic zone). The control flow logic should only allow cryptographic results to be driven to "sinks" when appropriate conditions are satisfied (typically when the final result for a cryptographic operation has been generated). When the appropriate conditions are not satisfied (i.e., before or during a cryptographic operation), the control flow logic should drive a safe default value to "sinks".

Effectiveness: High

Implementation

Designers/developers should add or modify existing control flow logic along any data flow paths that connect "sources" (signals with intermediate cryptographic state/results) with "sinks" (hardware module outputs and other signals outside of trusted cryptographic zone). The control flow logic should only allow cryptographic results to be driven to "sinks" when appropriate conditions are satisfied (typically when the final result for a cryptographic operation has been generated). When the appropriate conditions are not satisfied (i.e., before or during a cryptographic operation), the control flow logic should drive a safe default value to "sinks".

Effectiveness: High
+ Relationships
Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
+ Relevant to the view "Research Concepts" (View-1000)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 200 Exposure of Sensitive Information to an Unauthorized Actor
PeerOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 497 Exposure of Sensitive System Information to an Unauthorized Control Sphere
+ Relevant to the view "Hardware Design" (View-1194)
Nature Type ID Name
MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1205 Security Primitives and Cryptography Issues
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
Phase Note
Implementation

This can occur when intermediate cryptographic states are directly assigned to output wires or ports.
+ Applicable Platforms
Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
Languages

Class: Not Language-Specific (Undetermined Prevalence)

Architectures

Class: Not Architecture-Specific (Undetermined Prevalence)

Technologies

Class: System on Chip (Undetermined Prevalence)

+ Demonstrative Examples

Example 1


The following SystemVerilog code is a crypto module that takes input data and encrypts it by processing the data through multiple encryption rounds. Note: this example is derived from [REF-1469].

(bad code)
Example Language: Verilog 
01 | module crypto_core_with_leakage
02 | (
03 | input clk,
04 | input rst,
05 | input [127:0] data_i,
06 | output [127:0] data_o,
07 | output valid
08 | );
09 |
10 | localparam int total_rounds = 10;
11 | logic [3:0] round_id_q;
12 | logic [127:0] data_state_q, data_state_d;
13 | logic [127:0] key_state_q, key_state_d;
14 |
15 | crypto_algo_round u_algo_round (
16 | .clk (clk),
17 | .rst (rst),
18 | .round_i (round_id_q ),
19 | .key_i (key_state_q ),
20 | .data_i (data_state_q),
21 | .key_o (key_state_d ),
22 | .data_o (data_state_d)
23 | );
24 |
25 | always @(posedge clk) begin
26 | if (rst) begin
27 | data_state_q <= 0;
28 | key_state_q <= 0;
29 | round_id_q <= 0;
30 | end
31 | else begin
32 | case (round_id_q)
33 | total_rounds: begin
34 | data_state_q <= 0;
35 | key_state_q <= 0;
36 | round_id_q <= 0;
37 | end
38 |
39 | default: begin
40 | data_state_q <= data_state_d;
41 | key_state_q <= key_state_d;
42 | round_id_q <= round_id_q + 1;
43 | end
44 | endcase
45 | end
46 | end
47 |
48 | assign valid = (round_id_q == total_rounds) ? 1'b1 : 1'b0;
49 |
50 | assign data_o = data_state_q;
51 |
52 | endmodule

In line 50 above, data_state_q is assigned to data_o. Since data_state_q contains intermediate state/results, this allows an attacker to obtain these results through data_o.

In line 50 of the fixed logic below, while "data_state_q" does not contain the final result, a "sanitizing" mechanism drives a safe default value (i.e., 0) to "data_o" instead of the value of "data_state_q". In doing so, the mechanism prevents the exposure of intermediate state/results which could be used to break soundness of the cryptographic operation being performed. A real-world example of this weakness and mitigation can be seen in a pull request that was submitted to the OpenTitan Github repository [REF-1469].

(good code)
Example Language: Verilog 
01 | module crypto_core_without_leakage
02 | (
03 | input clk,
04 | input rst,
05 | input [127:0] data_i,
06 | output [127:0] data_o,
07 | output valid
08 | );
09 |
10 | localparam int total_rounds = 10;
11 | logic [3:0] round_id_q;
12 | logic [127:0] data_state_q, data_state_d;
13 | logic [127:0] key_state_q, key_state_d;
14 |
15 | crypto_algo_round u_algo_round (
16 | .clk (clk),
17 | .rst (rst),
18 | .round_i (round_id_q ),
19 | .key_i (key_state_q ),
20 | .data_i (data_state_q),
21 | .key_o (key_state_d ),
22 | .data_o (data_state_d)
23 | );
24 |
25 | always @(posedge clk) begin
26 | if (rst) begin
27 | data_state_q <= 0;
28 | key_state_q <= 0;
29 | round_id_q <= 0;
30 | end
31 | else begin
32 | case (round_id_q)
33 | total_rounds: begin
34 | data_state_q <= 0;
35 | key_state_q <= 0;
36 | round_id_q <= 0;
37 | end
38 |
39 | default: begin
40 | data_state_q <= data_state_d;
41 | key_state_q <= key_state_d;
42 | round_id_q <= round_id_q + 1;
43 | end
44 | endcase
45 | end
46 | end
47 |
48 | assign valid = (round_id_q == total_rounds) ? 1'b1 : 1'b0;
49 |
50 | assign data_o = (valid) ? data_state_q : 0;
51 |
52 | endmodule


+ Detection Methods
Method Details

Automated Static Analysis - Source Code

Automated static analysis can find some instances of this weakness by analyzing source register-transfer level (RTL) code without having to simulate it or analyze it with a formal verification engine. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (signals with intermediate cryptographic state/results) with "sinks" (hardware module outputs and other signals outside of trusted cryptographic zone) without any control flow.

Effectiveness: High

Note:

Static code analysis can sometimes lead to false positives.

Simulation / Emulation

Simulation/emulation based analysis can find some instances of this weakness by simulating source register-transfer level (RTL) code along with a set of assertions that incorporate the simulated values of relevant design signals. Typically, these assertions will capture desired or undesired behavior. Analysis can be improved by using simulation-based information flow tracking (IFT) to more precisely detect unexpected results.

Effectiveness: High

Note:

Simulation/emulation based analysis can sometimes lead to false negatives if the testbench does not drive the design to a design state in which the assertion would fail.

Formal Verification

Formal verification can find some instances of this weakness by exhaustively analyzing whether a given assertion holds true for a given hardware design specified in register-transfer level (RTL) code. Typically, these assertions will capture desired or undesired behavior. For this weakness, an assertion should check for undesired behavior in which one output is a signal that captures when a cryptographic algorithm has completely finished; another output is a signal with intermediate cryptographic state/results; and there is an assignment to a hardware module output or other signal outside of a trusted cryptographic zone.

Alternatively, when using a formal IFT verification, the same undesired behavior can be detected by checking if computation results can ever leak to an output when the cryptographic result is not copmlete.

Effectiveness: High

Note:

Formal verification may not scale for RTL designs with a large state space.

Manual Analysis

Manual analysis can find some instances of this weakness by manually reviewing relevant lines of source register-transfer level (RTL) code to detect potentially-vulnerable patterns. Typically, the reviewer will trace the sequence of assignments that connect "sources" (signals with intermediate cryptographic state/results) with "sinks" (hardware module outputs and other signals outside of trusted cryptographic zone). If this sequence of assignments is missing adequate control flow, then the weakness is likely to exist.

Effectiveness: Opportunistic

Note:

Manual analysis of source code is prone to errors (false positives and false negatives) and highly opportunistic.
+ Memberships
Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
Nature Type ID Name
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1417 Comprehensive Categorization: Sensitive Information Exposure
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1433 2025 MIHW Supplement: Expert Insights
+ Vulnerability Mapping Notes
Usage ALLOWED
(this CWE ID may be used to map to real-world vulnerabilities)
Reason Acceptable-Use

Rationale

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ References
[REF-1469] Andres Meza. "OpenTitan issue: [otp_ctrl] Prevent broadcast of scrambler's input/intermediate values #13043". 2022-06-03.
<https://github.com/lowRISC/opentitan/pull/13043>. (URL validated: 2025-04-02)
[REF-1470] Andres Meza, Francesco Restuccia, Jason Oberg, Dominic Rizzo and Ryan Kastner. "Security Verification of the OpenTitan Hardware Root of Trust". 2023-04-20.
<https://ieeexplore.ieee.org/document/10106105>. (URL validated: 2025-04-02)
[REF-1471] Jason Oberg. "Security Verification of an Open Source Hardware Root of Trust". 2022-08-03.
<https://cycuity.com/type/blog/security-verification-of-an-open-source-hardware-root-of-trust/>. (URL validated: 2025-04-02)
[REF-1472] Christophe Clavier, Quentin Isorez, Damien Marion and Antoine Wurcker. "Complete reverse-engineering of AES-like block ciphers by SCARE and FIRE attacks". 2014-10-23.
<https://doi.org/10.1007/s12095-014-0112-7>. (URL validated: 2025-04-02)
[REF-1473] Dirmanto Jap and Shivam Bhasin. "Practical Reverse Engineering of Secret Sboxes by Side-Channel Analysis". 2020-10.
<https://doi.org/10.1109/ISCAS45731.2020.9180848>. (URL validated: 2025-04-02)
+ Content History
+ Submissions
Submission Date Submitter Organization
2022-08-15
(CWE 4.17, 2025-04-03) 		Andres Meza University of California, San Diego
+ Modifications
Modification Date Modifier Organization
2025-09-09
(CWE 4.18, 2025-09-09) 		CWE Content Team MITRE
updated Relationships
Page Last Updated: September 09, 2025
 

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