Protecting Stored Data with Cryptography · 使用密码学保护存储数据
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| cryptography/krɪpˈtɒɡrəfi/ | 密码学 | mì mǎ xué |
| plaintext/ˈpleɪntekst/ | 明文 | míng wén |
| key/kiː/ | 密钥 | mì yào |
| ciphertext/ˈsaɪfətekst/ | 密文 | mì wén |
| keyspace/ˈkiːspeɪs/ | 密钥空间 | mì yào kōng jiān |
| symmetric encryption/sɪˈmetrɪk enˈkrɪpʃn/ | 对称加密 | duì chèn jiā mì |
| AES/ˌeɪ iː ˈes/ | 高级加密标准 | gāo jí jiā mì biāo zhǔn |
| block cipher/blɒk ˈsaɪfə/ | 分组密码 | fēn zǔ mì mǎ |
Encryption basics
- Cryptography 密码学 hides information.
- Encryption combines plaintext 明文 with a key 密钥 to make ciphertext 密文.
- The keyspace 密钥空间 is the number of possible keys — an n-bit key has $2^n$.
加密基础
- 密码学(cryptography)隐藏信息。
- 加密把明文(plaintext)与密钥(key)结合,生成密文(ciphertext)。
- 密钥空间(keyspace)是可能密钥的数量——n位密钥有 $2^n$ 个。
Symmetric encryption
- Symmetric encryption 对称加密 uses the same key to encrypt and decrypt.
- The standard is AES 高级加密标准, a block cipher 分组密码.
- Both sides need the same secret key — sharing it safely is the challenge.
对称加密
- 对称加密(symmetric encryption)用同一个密钥加密和解密。
- 标准是AES(高级加密标准),一种分组密码(block cipher)。
- 双方需要同一个秘密密钥——安全地分享它是挑战。
Symmetric encryption uses... · 对称加密使用……
Symmetric = one shared key. · 对称 = 共享一个密钥。
The standard modern symmetric block cipher is... · 现代标准对称分组密码是……
AES is the symmetric standard. · AES 是对称标准。
The scrambled output of an encryption algorithm is called ____. · 加密算法产生的乱码输出称为 ____。
Encryption turns plaintext into ciphertext. · 加密将明文转换为 密文。
Bigger keys, more security
- A larger keyspace takes an adversary longer to guess.
- Longer keys are more secure but slower.
- AES works on 128-bit blocks and secures Wi-Fi, browsing, and files.
更大的密钥,更多安全
- 更大的密钥空间让对手花更长时间猜测。
- 更长的密钥更安全但更慢。
- AES处理128位分组,保护Wi-Fi、浏览和文件。
Symmetric encryption is fast and strong, but it has one hard problem: both sides must already share the same secret key. Sending that key over an insecure channel would expose it — which is exactly what asymmetric cryptography solves next.
对称加密快速且强大,但它有一个难题:双方必须已经共享同一个秘密密钥。通过不安全的渠道发送该密钥会暴露它——而这正是下一节非对称密码学要解决的问题。
Encrypt by shifting letters · 通过移位字母进行加密
Encryption combines plaintext with a key. Here the key is the shift amount; only someone who knows it can decrypt. · 加密将明文与密钥结合。此处密钥为移位量；只有知道它的人才能解密。
A larger keyspace makes an encryption key harder to guess. · 更大的密钥空间使加密密钥更难猜测。
More possible keys = more guessing time. · 可能的密钥越多 = 猜测时间越长。
How many possible keys does a 4-bit key have? (2^4) · 4位密钥有多少种可能？(2^4)
$2^4 = 16$ possible keys. · $2^4 = 16$ 种可能密钥。
A simple Caesar cipher shifts each letter by a fixed key. With key = 3, CAT becomes FDW. Only someone who knows the shift (the key) can turn FDW back into CAT. Real algorithms like AES use far larger keyspaces, but the idea is the same.
一个简单的凯撒密码把每个字母按固定密钥移位。密钥=3时,CAT 变成 FDW。只有知道移位量(密钥)的人才能把 FDW 变回 CAT。像AES这样的真实算法使用大得多的密钥空间,但道理相同。
Cryptography turns plaintext into ciphertext using a key. A bigger keyspace ($2^n$ for an n-bit key) is harder to break. Symmetric encryption (e.g. AES) uses one shared key — fast and strong, but the shared key must be exchanged safely.
密码学用密钥把明文变成密文。更大的密钥空间(n位密钥为 $2^n$)更难破解。对称加密(如AES)用一个共享密钥——快速且强大,但共享密钥必须安全地交换。