← ToolBox / 凯撒密码移位

🕵️ Caesar Cipher Shift

Shift English letters by 0-25 to demonstrate the Caesar cipher, for teaching classical substitution ciphers.

字母位置 A=0

移位量

模数

C = (P + k) mod 26
P = (C − k) mod 26

仅演示字母位置计算，不含完整加解密。

📚 深度解析：凯撒密码移位

示例：HELLO 移位 3

H→K,E→H,L→O,L→O,O→R → "KHOOR"；移位 0 或 26 为明文。

Item	Formula / Rule	Source / Standard
Encryption	C = (P + k) mod 26 with P the plaintext letter index and k the shift	Suetonius, De Vita Caesarum, Life of Julius Caesar §56
Decryption	P = (C − k + 26) mod 26, keeping the result within 0 to 25	Kahn, The Codebreakers, 1967 — classical substitution ciphers
Effective key space	Only 25 shifts from 1 to 25 are meaningful; k = 0 and k = 26 leave text unchanged	Kahn, The Codebreakers, 1967 — frequency analysis