________ ciphers place each resulting bit in the original position.

Question

BlackTom AI · Accepted Answer

Substitution ciphers replace each plaintext symbol (or bit) with another symbol while leaving its position unchanged.

1. Relevant knowledge points and concepts
- Substitution cipher: a mapping that replaces each element of the plaintext alphabet with a corresponding ciphertext element; indices (positions) remain the same. Example: Caesar cipher shifts letters but does not move their positions.
- Transposition cipher: a permutation of plaintext symbols that rearranges positions without changing the actual symbols.
- “Bit” interpretation: substitution can act on individual bits (0→1, 1→0 or other bijections) while keeping the i-th bit in the i-th place; transposition would move the i-th bit to some other index.

2. Step-by-step reasoning
- The sentence asks which kind of cipher “place each resulting bit in the original position.” That implies the output symbol for position i resides at position i (positions preserved).
- Which option matches that property? Substitution transforms the value at position i but keeps it in position i. Transposition would move it to a different position.

3. Intermediate examples (illustrating the mechanism)
- Bit example: plaintext bits 0 1 1 0. A substitution mapping 0→1, 1→0 gives ciphertext 1 0 0 1 — each bit’s index is unchanged.
- Letter example: plaintext “HELLO” shifted by 3 (Caesar) → “KHOOR”; letters remain at their original positions (H→K at pos1, E→H at pos2, etc.).

4. Why the correct answer is correct
- The defining property in the prompt is position preservation. Substitution ciphers change symbols but not order, so they meet the stated condition directly.

5. Why other options are incorrect
- Subtraction: not a standard cipher type and doesn’t describe position behavior.
- Transmutation: not a conventional cryptographic term here.
- Transposition: explicitly reorders symbols, so it does the opposite of preserving original positions.

6. Conclusion
Confirmed final answer: Substitution.

________ ciphers place each resulting bit in the original position.单项选择题

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