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The Magic of Information Flow Control: How to Protect Your Secret Data?
In the digital age, individuals and businesses face increasing risks of data leakage. In the context of information theory, information flow refers to the process of transferring data from one variable x to another variable y. No system wants to leak confidential information, which not only involves personal privacy but may also cause significant losses to the company.
There are many ways to limit the disclosure of information, such as access control lists, firewalls, and encryption technology. However, although these methods limit the release of information to a certain extent, they cannot guarantee that the information will not be leaked.
As technology advances, the methods of ensuring data security have also changed greatly. For example, access control lists can prevent unauthorized access to files, but they cannot control what happens to the data once it is in use. Similarly, although encryption technology can transmit information privately in an insecure channel, the confidentiality of the data will be threatened once it is decrypted. Therefore, it becomes particularly important to understand the control of information flow.
Explicit Streams and Side Messages
Information flows can be roughly divided into two categories: explicit flows and bypass flows. Explicit flow is when a secret is explicitly leaked into a publicly observable variable, for example:
var l, h; l := h;
On the other hand, side-streams exploit certain characteristics such as execution time or power consumption to leak information. For example, in a condition, if h is true, some time-consuming work will be performed, which allows an attacker to infer h based on the time taken by the program. The value of .
Implicit information flow is also part of the bypass flow. While the control flow of a program is based on private data, public variables can imply some secret information.
Non-interference policy
Non-interference is a policy that emphasizes that an attacker should not be able to distinguish between two computations based on their output if they differ only in their secret inputs. Nevertheless, this policy is too restrictive to be applied in actual procedures.
For example, a password-checking program might need to reveal some secret information when necessary: namely, whether the entered password is correct. This allows an attacker to obtain useful information even when the program rejects the password, e.g. the attempted password entered was not valid.
Information flow control mechanism
Information flow control mechanisms are designed to enforce information flow policies. To achieve this goal, several methods have been proposed to implement information flow strategies. Runtime mechanisms can label data at the operating system and programming language level, while static program analysis ensures that the information flow in the program follows the corresponding policies.
However, dynamic analysis techniques cannot observe all execution paths and therefore cannot guarantee both robustness and accuracy. To ensure that they do not interfere with policy enforcement, these techniques often require terminating execution that could potentially leak sensitive information, or ignoring updates that could leak information.
Safe Type System
A safe type system adds an important element to programming languages, allowing every expression to carry a safety label in addition to having a type (such as Boolean or integer). The benefit of doing this is that, through type checking, if the program passes the check, it can ensure that the flow policy is followed, thereby avoiding improper information flow.
For example, if a variable is marked as a high-security type, then the variable should not change a variable of a low-security type, thereby protecting confidential information from being leaked.
Declassification processing
In real-world applications, the strictness of the non-interference policy makes it impractical. Therefore, many schemes for permitting the release of information have been proposed to achieve the goal of controlled release. These schemes are also known as information declassification. Robust declassification must ensure that an active attacker cannot manipulate the system to gain access to secrets beyond what a passive attacker knows.
SummaryInformation flow control is becoming increasingly important in modern programming and data protection. However, how to effectively ensure data security in practical applications remains a challenge that needs to be addressed. Are you prepared to deal with these potential threats?
