question_id int64 1 19 | category stringclasses 4
values | question stringlengths 22 181 | options listlengths 10 10 | answer stringclasses 9
values | answer_id int64 0 9 | cot_content stringlengths 23 546 | difficulty stringclasses 3
values | score int64 2 10 | language stringclasses 2
values | source stringclasses 1
value |
|---|---|---|---|---|---|---|---|---|---|---|
1 | basic knowledge | Identify the cipher that involves shifting each letter of the plaintext by a fixed number of positions down the alphabet | [
"Enigma machine",
"Bacon's cipher",
"Atbash cipher",
"One-time pad",
"Transposition cipher",
"Playfair cipher",
"Caesar cipher",
"Affine cipher",
"Vigenere cipher",
"Rail Fence cipher"
] | G | 6 | The Caesar cipher shifts letters by a fixed offset. For example, with a shift of 3, A->D, B->E, etc. It’s a simple substitution cipher. None of the others use a single fixed shift for all letters (Vigenere uses a repeating keyword, Playfair uses digraphs, etc.), so the cipher described is the Caesar cipher. | Easy | 2 | English | exam |
2 | basic knowledge | How many non-zero shift values (keys) are possible in the standard Caesar cipher (using the English alphabet)? | [
"12",
"32",
"13",
"52",
"23",
"27",
"24",
"21",
"26",
"25"
] | J | 9 | In a 26-letter alphabet, there are 25 possible non-zero shifts (1 through 25). A shift of 0 is typically not counted as a valid key (since it leaves text unchanged). Thus 25 is the number of distinct non-trivial Caesar cipher keys. | Easy | 2 | English | exam |
3 | calculate | Encrypt the plaintext "HELLO" using a Caesar cipher with a shift of 3 to the right | [
"IFMMP",
"NKRRU",
"ROVVY",
"KHOOR",
"JGNNQ",
"MJQQT",
"URYYB",
"'LIPPS",
"HELLO",
"ESCCB"
] | D | 3 | Shifting "HELLO" three letters forward: H->K, E->H, L->O, L->O, O->R, produces "KHOOR". Among the options, "KHOOR" matches this result. | Normal | 5 | English | exam |
4 | calculate | Decrypt the ciphertext "ZHOFRPH" which was encrypted with a Caesar cipher using a shift of 3 to the right | [
"ATTACK AT DAWN",
"ATTEND AT DUSK",
"ATTACK AT DUSK",
"DEFFENSE ON HERE",
"RETREAT AT DAWN",
"ATTACK BY NIGHT",
"DEFEND AT DAWN",
"ATTACH AT DAWN",
"ATTACK AT NOON",
"SURRENDER GO HOME"
] | A | 0 | ZHOFRPH decrypted with a shift of -3 yields "WELCOME". The phrase "WELCOME" fits logically as English text. | Normal | 5 | English | exam |
5 | basic knowledge | Which of the following is a major weakness of the Caesar cipher? | [
"It completely disguises the letter frequency of the original message.",
"It was considered secure enough for use in World War II communications.",
"It jumbles the positions of letters instead of substituting them.",
"It requires large prime numbers as part of its encryption algorithm.",
"It has only 25 pos... | E | 4 | The Caesar cipher’s key space is extremely small. With only 25 non-zero shifts, brute-force attacks are trivial. | Easy | 2 | English | exam |
6 | algorithm | In an Affine cipher defined by E(x) = (ax + b) mod 26, which condition must the multiplier a satisfy for the cipher to be valid (invertible)? | [
"a must be greater than 26.",
"a must be a prime number.",
"a must be an odd integer.",
"a must be one of the factors of 26.",
"gcd(a,26)=1.",
"a must equal 25.",
"a must be a multiple of 13.",
"a must be even.",
"There is no restriction on a (any 0≤a<26 will work).",
"a must be greater than 26."
... | E | 4 | For an Affine cipher mod 26, a must be coprime with 26 (gcd(a,26)=1) to ensure invertibility. | Normal | 5 | English | exam |
7 | algorithm | How many distinct keys (different (a,b) pairs) are possible in an Affine cipher on the English alphabet? | [
"144",
"650",
"360",
"300",
"312",
"26",
"676",
"52",
"156",
"338"
] | E | 4 | There are 12 possible a values coprime with 26 and 26 possible b values, totaling 312 unique keys. | Normal | 5 | English | exam |
8 | calculate | Using an Affine cipher with a=5 and b=8, what is the encryption of plaintext 'C'? | [
"S",
"F",
"W",
"K",
"A",
"M",
"Z",
"I",
"G",
"T"
] | A | 0 | Numeric value of C is 2. E(C)=5*2+8=18 mod 26, which corresponds to S. | Normal | 5 | English | exam |
9 | basic knowledge | The Data Encryption Standard (DES) uses a block size of ___ and an effective key length of ___. | [
"64 bits; 128 bits",
"48 bits; 48bits",
"128 bits; 56 bits",
"64 bits; 64bits",
"16 bytes; 8 bytes",
"64 bits; 56bits",
"128 bits; 112 bits",
"32 bits; 64bits",
"56 bits; 64 bits",
"8 bits; 56 bits"
] | F | 5 | DES operates on 64-bit blocks with a 56-bit effective key length. | Easy | 2 | English | exam |
10 | algorithm | How many Feistel rounds does the DES encryption algorithm perform? | [
"16",
"14",
"12",
"8",
"15",
"20",
"32",
"24",
"64",
"10"
] | A | 0 | DES performs 16 rounds of Feistel network. | Normal | 5 | English | exam |
11 | basic knowledge | The DES algorithm can be classified as which type of cipher structure? | [
"Public-key cipher",
"Substitution-permutation network",
"Rotor machine cipher",
"Codebook cipher",
"Feistel network block cipher",
"Polyalphabetic substitution cipher",
"Transposition-based cipher",
"Stream cipher",
"Asymmetric cipher",
"Hash function"
] | E | 4 | DES is a Feistel network block cipher. | Easy | 2 | English | exam |
12 | basic knowledge | What is Triple DES (3DES) and why was it introduced? | [
"Failed replacement for DES",
"Encrypt-decrypt-encrypt with same key",
"Reduce computational cost by 3",
"DES on 3 parallel processors",
"Early AES name",
"Three 56-bit keys concatenated",
"64-bit key split for encryption-decryption-re-encryption",
"Triples block size",
"Encrypt DES three times with... | I | 8 | 3DES applies DES three times with multiple keys to increase security. | Normal | 5 | English | exam |
13 | basic knowledge | Which key lengths are supported by AES? | [
"256 & 512 bits",
"512 bits",
"1024 bits",
"160 & 224 bits",
"128 bits only",
"64 & 128 bits",
"128, 192, and 256 bits",
"56 & 112 bits",
"192 & 384 bits",
"Any key length"
] | G | 6 | AES supports 128, 192, and 256-bit keys. | Easy | 2 | English | exam |
14 | algorithm | What is the block size of AES? | [
"16 bytes",
"32 bytes",
"192 bits",
"64 bits",
"8 bytes",
"256 bits",
"variable",
"512 bits",
"128 bits",
"16 bits"
] | I | 8 | AES block size is fixed at 128 bits. | Easy | 2 | English | exam |
15 | algorithm | How many rounds does AES-128 perform? | [
"8",
"10",
"9",
"128",
"12",
"14",
"20",
"13",
"11",
"16"
] | B | 1 | AES-128 uses 10 rounds. | Normal | 5 | English | exam |
16 | challenge | 19世纪末，考古队发现了一份疑似藏宝图的密文手稿，内容如下： 密文：PBL VZZLLP CZ EPOCLZ OUGZO NOA UUFDBHA KUR WMBY 已知加密过程分两步： 1.使用凯撒密码对明文进行加密得到中间文本，移位数为3。 2.使用维吉尼亚密码再对中间文本进行加密，得到该密文，密钥为treasure。 请结合上述信息解密，并选择正确的明文。 | [
"THE SECRET IS BURIED UNDER THE ANCIENT OAK TREE",
"FIND THE HIDDEN MESSAGE IN THE SECOND PARAGRAPH",
"SECRET COORDINATES ARE MARKED ON THE OLD MAP",
"LOOK FOR THE CLOCKTOWER AND WALK TWENTY STEPS EAST",
"THE SECRET MESSAGE IS ENCODED IN THIS PARAGRAPH",
"SOLVE THE CIPHER TO DISCOVER THE BURIED GOLD",
"... | A | 0 | 让我们一步步进行思考。首先，应该获取解密过程，加密过程分为2步：1. 使用移位数为3的凯撒密码对明文加密，得到中间文本。2. 使用密钥为treasure的维吉尼亚密码对上一步中得到的中间文本再进行加密，并得到最终密文。那么，解密过程就应该反过来，先使用密钥treasure对密文进行维吉尼亚密码解密，得到中间文本，然后使用移位数3对中间文本进行凯撒密码解密。让我们开始尝试对密文进行解密，维吉尼亚密码解密的过程应该是用密钥treasure替换英文字母表的前8位，然后对密文进行反向替换，得到的中间文本为WKH VHFUHW LV EXULHG XQGHU WKH DQFLHQW RDN WUHH，关于中间文本还有一点值得注意："WKH"频... | Hard | 10 | 中文 | exam |
17 | basic knowledge | 非对称加密算法RSA是密码学中的一种重要算法。以下关于RSA的描述中，错误的是？ | [
"RSA是一种基于大整数分解难题的非对称加密算法。",
"RSA的密钥由公钥和私钥构成，公钥可以公开，私钥必须保密。",
"RSA的加密和解密过程是不对称的，使用不同的密钥进行操作。",
"RSA的密钥长度可以任意选择，没有限制。",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A"
] | D | 3 | RSA 是一种经典的非对称加密算法，其安全性基于大整数分解的计算难题。在非对称体系中，公钥和私钥分别用于加密与解密，且两者在功能上并不对称。理解这些基本原理是判断选项真伪的前提。逐项验证：(A) “RSA 基于大整数分解难题” —— 与常见教材一致，是 RSA 安全性的根基，因此正确。(B) “密钥由公钥和私钥构成，公钥公开、私钥保密” —— 完全符合非对称加密的定义，也是 RSA 实践中的基本要求，因此正确。(C) “加密和解密过程是不对称的，使用不同的密钥进行操作” —— 正是非对称加密的核心特征，故此描述也正确。(D) 声称“RSA 的密钥长度可以任意选择，没有限制”。表面上看，不同应用场景确实可以选用不同位数的密钥，但为了抵... | Hard | 10 | 中文 | exam |
18 | basic knowledge | 以下哪种技术常用于防止密码系统中的重放攻击？ | [
"时间戳",
"序列号",
"挑战-响应机制",
"以上都是",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A"
] | D | 3 | 首先，确定攻击类型：重放攻击是指攻击者截获并重发之前的有效消息以欺骗系统。然后，对选项进行分析：时间戳能让接收方检查消息的“新鲜度”，过时的消息将被丢弃；序列号通过为每条消息分配唯一且递增的编号，防止重复接收；挑战—响应机制（nonce）保证每次会话使用不同的随机值，重放旧响应会因随机值不匹配而失败。根据分析结果，以上3种方法均能抵御重放攻击，因此答案是(D)以上都是 | Normal | 5 | 中文 | exam |
19 | basic knowledge | 零知识证明技术的‘零知识’指的是能够在不泄露（）的情况下完成证明？ | [
"证明者身份",
"证明过程",
"被证明内容",
"任何信息",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A",
"N/A"
] | C | 2 | 零知识证明的特性为：允许互不信任的通信双方之间证明某个命题的有效性，同时不泄露任何额外信息。“任何额外信息”的表述看起来接近(D)任何信息，但看一看(A)(B)两个选项，如果不知道证明者身份，那证明过程就没有意义；如果不知道证明过程，那么就无法知道该通过什么信息判断证明有效。而且，零知识证明的协议应该是公开的。所以，零知识证明的保护范围应该只有“被证明内容”，答案是(C)被证明内容。 | Hard | 10 | 中文 | exam |
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