Excerpt
This post explains the key differences between the SHA-384 and SHA-512 hash functions, analyzing factors like digest size, padding scheme, efficiency, and collision resistance to understand why SHA-384 is considered more secure.
Cryptographic hash functions like SHA-384 and SHA-512 play a vital role in protecting the integrity and authenticity of data in systems. While closely related, subtle differences in their design make SHA-384 the more secure algorithm overall. In this post, we’ll compare the two and see why SHA-384 has the edge.
Introduction
SHA-384 and SHA-512 belong to the SHA-2 family of cryptographic hash functions published by NIST. They are commonly used for applications like digital signatures, password storage, blockchain ledgers, and data integrity verification.
Though SHA-512 has a larger digest size, cryptanalysis shows that SHA-384 actually provides stronger security assurances. Let’s examine why by looking at their key differences.
Overview of SHA-384 and SHA-512
SHA-384 and SHA-512 are hash functions that produce a 384-bit and 512-bit hash digest respectively for any input message.
They follow similar algorithms based on the Merkle–Damgård construction, using iterative compression and cryptographic transformations like bitwise operations, modular additions, rotations, and permutations.
Both are designed to provide strong cryptographic security with a minimal risk of collisions.
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Key Differences Between SHA-384 and SHA-512
Digest Size
SHA-384 has a digest size of 384 bits while SHA-512 is 512 bits. Longer digests theoretically offer more resistance to collision attacks.
However, beyond a point any additional bits provide diminishing returns while still increasing computational load. Cryptanalysis confirms this, with SHA-512 offering virtually no extra security over SHA-384 despite the larger digest.
Padding Scheme
The padding scheme in SHA-384 makes its output less susceptible to extension attacks compared to SHA-512. The padding bytes are dependent on the message length in SHA-384 while fixed in SHA-512.
Though not a serious concern in practice, from a standards perspective SHA-384 has the edge.
Speed and Efficiency
SHA-512 requires more rounds of computation than SHA-384 - 80 vs 64. With the minimal security gains from the increased digest size, SHA-384 proves more efficient in performance benchmarks.
Collision Resistance
A fundamental requirement of secure hash functions is resistance to collisions where two different input values produce the same hash digest.
Cryptographic research shows SHA-384 and SHA-512 have similar collision resistance despite their different digest sizes. The theoretically possible attacks are still infeasible with current computing capacity.
Overall, SHA-384 is considered at least as collision resistant as SHA-512, if not better.
Security Strength
NIST classifies SHA-384 as providing 192 bits of security strength. This means the best known attack requires 2^192 operations, which is computationally infeasible with current technology.
SHA-512 is rated at 256 bits of security, not twice of SHA-384 as might be expected from the digest sizes. This highlights the marginal gains of larger digests.
So while SHA-512 has a higher security rating on paper, SHA-384 is almost just as resistant to real-world cryptographic attacks.
Conclusion
Subtle differences in their design and padding scheme makes SHA-384 theoretically more secure than SHA-512. With digest sizes beyond 384-bits providing minimal gains, SHA-384 also proves more efficient.
For most applications, either algorithm provides ample protection against collision attacks with current computing capacity. But from a standards and efficiency perspective, SHA-384 has the edge as the most secure SHA-2 variant.
Understanding the security nuances of these fundamental cryptographic building blocks highlights the care and research required in developing robust security standards. Encryption relies on strong underlying hash primitives like SHA-384. Carefully designed and implemented, they can effectively safeguard the integrity of modern digital systems and data.
