問91
頻出度★★★
デジタル署名やブロックチェーンで用いられるハッシュ関数には, SHA-256, SHA-512などがある。このようなハッシュ関数に関する記述として, 適切なものはどれか。
令和8年度 ITパスポート試験 問91
This question's explanation and your answers so far.
解説
問 91
Incorrectア
A hash function has one-wayness (you can compute a hash value from the original data, but not the reverse). Feeding a hash value back into the same function only produces another hash value; the original data cannot be restored.
Incorrectイ
As with SHA-256 and SHA-512, different hash functions have different internal algorithms and different output bit lengths. Even when the same data is input, the resulting hash value normally differs from one function to another, so they are not all the same.
- ウ
正解 A hash function is a deterministic function: inputting the same data into the same hash function always yields the same fixed-length hash value, no matter how many times it is computed. It is precisely this reproducibility that lets it be used for tamper detection in digital signatures and blockchain (the sender and receiver each obtain the same value from the same data and confirm that they match). Therefore, choice ウ, which states that “when the same hash function is used, as long as the input data is the same, the hash value obtained is always the same,” is appropriate.
Incorrectエ
A hash function is a many-to-one mapping and has one-wayness, so there is no inverse function that maps a hash value back to the original data. The statement that an inverse function exists and can restore the original data contradicts the definition of a hash function.
ここがポイント
- The three key properties of a hash function: one-wayness (the original data cannot be restored from the hash value), fixed-length output, and always producing the same output for the same input (determinism).
- Tamper detection in digital signatures and blockchain relies on this determinism (reproducibility) as its premise.
用語