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How to choose the perfect key size in modern encryption? How strong is your security?
In today's digital age, information security has become an increasingly important issue. As cybercrime becomes increasingly rampant, how to ensure the security of our data has become a challenge that everyone should face. Key size is an important part of the encryption system, and choosing the appropriate key size is the key to protecting data security.
The security level of a key is usually expressed in terms of "security bits." This number reflects the amount of computation required to crack the key, usually expressed as 2 raised to the nth power. For example, for AES-128 (128-bit key), the attacker needs to perform 2^128 calculations to successfully crack. Therefore, choosing an appropriate key size is crucial to ensuring information security.
Security is an indicator of the strength of a cryptographic primitive (such as an encryption algorithm or hash function). For a well-designed system, the relationship between key size and security should be clear.
Key size in symmetric encryption
Symmetric encryption algorithms usually have well-defined security statements, and the key size directly affects the difficulty of attack. For example, for a symmetric encryption algorithm with a key size of n bits, its security level is generally considered to be equal to the key size, which means that the amount of calculation required for brute force cracking is extremely high. Taking SHA-256 as an example, this cryptographic hash function provides 256-bit preimage resistance and 128-bit collision resistance, indicating its ultra-high security.
In symmetric encryption, it is a simple fact that the security statement is usually equal to the key size.
Challenges of asymmetric encryption
Unlike symmetric encryption, asymmetric encryption algorithms such as RSA rely on the computational feasibility of mathematical problems. These algorithms are efficient in computing one direction, but are quite difficult for an attacker to compromise their security. Adjusting their security level according to the current best attack methods is the basis for designing these algorithms. For a 128-bit security level, NIST and ENISA recommend a 3072-bit key, and the IETF recommends a 3253-bit key.
The emergence of various recommendations has made the security level of asymmetric encryption algorithms more clear, thereby providing clearer guidance to users.
Actual security level selection
According to NIST recommendations, all keys should be protected with the same or higher security level algorithms. This means that if the security requirement of a key is 128 bits, then it can only be transmitted with a security algorithm of 128 bits or higher. This is particularly important because as technology evolves, standards considered safe in the past may not continue to meet current needs.
According to NIST recommendations, the trade-off in security levels between different algorithms will affect the overall performance of encryption and reduce possible vulnerabilities.
Encryption primitives considered "broken"
When an attack is found that requires less computation than its declared security level, the cryptographic primitive is considered broken. However, not all discovered attacks are actually feasible. Many of the attacks currently demonstrated require less than 240 operations, which would take just a few hours on a typical PC. It follows that the balance between key size and attack cost is another important aspect to consider in current encryption practices.
Future key size recommendations
As computing power increases and new attack methods emerge, we need to re-evaluate our key size choices. For most applications, a key size of at least 256 bits is recommended. For specific high-security application scenarios, larger keys may be required. For example, under the influence of quantum computing, current encryption standards may need to be adjusted to meet the challenges of new types of attacks in the future.
In the face of ever-evolving encryption technologies and attack methods, can we find stronger security methods to protect our data from future threats?
