The Secure Hash Algorithm design closely models, and is based on, the hash function __________ .

Question

BlackTom AI · Accepted Answer

SHA’s internal structure—an iterative compression function using 32-bit words, modular addition, bitwise logical functions, message padding, and the Merkle–Damgård construction—follows the design pattern introduced by MD4.

1) Relevant knowledge points and concepts
- MD4 (Ronald Rivest, 1990) defined an iterative hash based on rounds of simple non-linear functions, additions, and rotations; it produced a 128-bit digest.
- The Merkle–Damgård construction and message padding/length-encoding are central to early hash designs.
- SHA (the original Secure Hash Algorithm family, specified in FIPS 180) was created by NSA/NIST in the early 1990s and adopted that same structural approach.
- MD5 (1992) is a successor to MD4 with modifications; FIPS 180 is the standards document specifying SHA; RFC 4634 documents the SHA family.

2) Step-by-step reasoning
- MD4 introduced an architecture of multiple rounds operating on 32-bit words, mixing non-linear functions, additions, and rotations.
- When SHA was designed, its authors used MD4’s iterative compression paradigm as the model, preserving the notion of rounds, word-based operations, padding, and chaining variables.
- SHA changed specifics (different logical functions, constants, and an expanded digest size for SHA-1), but the overall blueprint is directly traceable to MD4’s design.

3) Calculations
- Not applicable (no numeric computation required). The comparison is structural and historical.

4) Why the correct answer is correct
- Historical records and cryptographic literature explicitly state that the Secure Hash Algorithm’s design was modeled on MD4. The algorithms share the same family traits (iterative compression, Merkle–Damgård style), even though SHA evolved parameters for improved properties and a longer digest.

5) Why other options are incorrect
- MD5: Derived from MD4 but is a later revision; SHA is based on MD4’s original design, not on MD5.
- FIPS 180: This is the standards document that specifies SHA, not the hash function on which SHA was modeled.
- RFC 4634: An informational RFC describing hash algorithms (including SHA), not the underlying hash function model.

6) Conclusion
Therefore, the Secure Hash Algorithm design closely models and is based on MD4. The correct answer is MD4.

The Secure Hash Algorithm design closely models, and is based on, the hash function __________ .单项选择题

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