Cipher
The word came to Europe with Arabic numerals. From "zero," it came to mean "any numeral" (early 15c.), then (first in French and Italian) "secret way of writing; coded message" (a sense first attested in English 1520s), because early codes often substituted numbers for letters.
来自古法语cifre，零，来自意大利语cifra，零，来自阿拉伯语sifr，零，来自s-f-r，空的，空无，词源同zero.上面的引文给出的路径是：从零扩展为数字，再因早期密码常以数字替代字母，引申为密码。
——收入 词语的化石层