crypto4c-ch00-导读

crypto加密原理Crypto, short for cryptography, is the practice and study of techniques for secure communication in the presence of third parties. It is used to secure the information and communication between parties through the use of codes and ciphers.加密，即密码学，是在第三方存在时用于安全通信的技术的实践和研究。

它用于通过使用代码和密码来保护各方之间的信息和通信。

One of the key principles of cryptography is the use of algorithms to encrypt and decrypt messages. These algorithms use keys to perform the encryption and decryption processes, ensuring that only the intended recipients can access the information.密码学的一个关键原则是使用算法来加密和解密消息。

这些算法使用密钥来执行加密和解密过程，确保只有预期的接收者才能访问信息。

There are two main types of cryptography: symmetric and asymmetric. Symmetric cryptography uses the same key for both encryption and decryption, while asymmetric cryptography uses apair of public and private keys for the encryption and decryption processes.密码学主要有两种类型：对称加密和非对称加密。

Linux内核提供了丰富的加密和密码学功能，这些功能可以在内核中使用，而不需要依赖用户空间的库或工具。

这些功能包括对称加密、非对称加密、哈希函数、伪随机数生成和数字签名等。

以下是一些常见的Linux 内核crypto 库的用法示例：1. **对称加密**：使用内核的对称加密API，你可以进行对称加密操作，如AES、DES等。

下面是一个使用AES 加密的示例：```c#include <linux/crypto.h>#include <linux/scatterlist.h>#include <crypto/skcipher.h>/* 加密函数*/void aes_encrypt(const u8 *input, u8 *output, struct crypto_skcipher *tfm){struct skcipher_request *req = NULL;struct scatterlist sg_in, sg_out;int ret;req = skcipher_request_alloc(tfm, GFP_KERNEL);if (!req) {printk(KERN_ERR "skcipher_request_alloc failed\n");return;}sg_init_one(&sg_in, input, AES_BLOCK_SIZE);sg_init_one(&sg_out, output, AES_BLOCK_SIZE);skcipher_request_set_crypt(req, &sg_in, &sg_out, AES_BLOCK_SIZE, NULL);ret = crypto_skcipher_encrypt(req);if (ret) {printk(KERN_ERR "crypto_skcipher_encrypt failed: %d\n", ret);}skcipher_request_free(req);}```2. **非对称加密**：你也可以在内核中使用非对称加密，如RSA。

Introduction to Cryptocurrencies∗Stefan Dziembowski†University of WarsawS.Dziembowski@.plABSTRACTWe provide a research-oriented introduction to the crypto-graphic currencies.We start with a description of Bitcoin and its main design principles.We then discuss some of its weaknesses,and show some ideas for dealing with them.We also talk about the mechanics of the mining pools and ideas for discouraging the mining pool creation.We provide an introduction to the smart contracts,and give some examples of them,including the multiparty lotteries.We then present alternative currencies that were designed to remedy some of the problems of Bitcoin.In particular, we talk about the Litecoin,the Primecoin,the Permacoin, the Zerocoin,the Proofs of Stake and the Proofs of Space. We also discuss the most important research challenges in this area.Categories and Subject DescriptorsK.4.4[Computing Milieux]:Computers and Society–Payment schemes;Distributed commercial transactions;Cy-bercash,digital cashKeywordscryptocurrencies;distributed cryptography1.INTRODUCTIONThe cryptographic currencies(also dubbed the cryptocur-rencies)are a fascinating recent concept whose popularity exploded in the past few years.Their main distinguishing feature is that they are not controlled by any single entity.∗A longer version of this document is available at .pl/Dziembowski/talks/bitcoin-tutorial.pdf.Slides from this tutorial are available at.pl/Dziembowski/talks.†Supported by the Foundation for Polish Science WELCOME/2010-4/2grant founded within the frame-work of the EU Innovative Economy(National Cohesion Strategy)Operational ProgrammePermission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full cita-tion on thefirst page.Copyrights for third-party components of this work must be honored.For all other uses,contact the Owner/Author(s).Copyright is held by the owner/author(s).CCS’15,October12–16,2015,Denver,Colorado,USA.ACM978-1-4503-3832-5/15/10.Instead,they are jointly maintained by their anonymous users connected via peer-to-peer networks.Their security is based purely on the security of the underlying crypto-graphic primitives,and on some global assumptions about the behavior of their users(like,e.g.,an assumption that a large fraction of the computing power is controlled by the honest participants).Historically thefirst,and the most prominent cryptocur-rency is the Bitcoin,introduced in2008by Satoshi Naka-moto[9].Probably the most intriguing technical innovations of Bitcoin are:the mechanism for reaching consensus in fully distributed peer-to-peer networks(the so-called blockchain technology),and the transaction syntax that allows to ex-ecute distributedfinancial operations that are much more complex than simple money transfers.Even the sheerfinancial importance of the cryptocurencies makes them an interesting research area.In our opinion, however,what makes this topic even more fascinating are the conceptual ideas behind it.These aspects will be the main focus of this tutorial.Goal of this tutorial.The goal of this tutorial is to provide a research-oriented introduction to the cryptocur-rencies.We will present the main principles of the Bitcoin design,discuss some of its weaknesses,show some ideas for its improvements and for other currencies,and discuss the most important research challenges in this area.Intended audience and prerequisite knowledge. This tutorial will be suitable for all the ACM CCS partic-ipants,both coming from the academia and from the in-dustry.We will assume familiarity with the basic crypto-graphic primitives,such as the hash functions,the signature schemes,and encryption.No prior knowledge of Bitcoin or other cryptographic currencies is required.2.OVERVIEW2.1IntroductionWe will start with a brief overview of the history of the cryptocurrencies.We will identify the mainfinancial and social aspects that contributed to the success of Bitcoin,and mention some opinions of prominent economists about the cryptocurrencies,both those supporting this idea,and those that are skeptical about it.We will show how the popularity of Bitcoin grew over time,and how its pricefluctuated.We will also mention some important events in the history of the Bitcoin community(like the MtGox collapase).DOI: /10.1145/2810103.2812704.We will introduce the transaction ledger(the blockchain), as a technique that can be used to prevent double-spending of electronic cash.We will point out that the Sybil attacks should be taken into account when designing a protocol that emulates such a ledger.We will explain what are the Proofs of Work(PoWs)and how to apply them to thwart the Sybil attacks.We will show how the Bitcoin ledger is maintained by the users called miners that solve the PoWs,in a process called mining.We will explain the concept of the hashrate and show how the total hashrate of Bitcoin users changed over the time.We will also describe how the hardness of Bitcoin’s PoW’s is adjusted to the changing hashrate.We will also talk about the Bitcoin transaction syntax.2.3Bitcoin mining poolsMining pools are coalitions of miners that share the re-ward from mining new blocks.We will discuss the economic reasons for joining the mining pools(reducing the variance of the mining reward).We will then talk about the mechan-ics of the mining pool reward systems and their weaknesses. We will also show how mining pools can be decentralized vie the so-called peer-to-peer mining technique.Discouraging the mining pool creation.We will ex-plain the risks behind the pooled miming.In particular,we will point out that it leads to the centralization of the control over mining.We will then discuss some ideas for the Bitcoin modifications that discourage the mining pool creation[8].2.4Security weaknesses of BitcoinWe will discuss the quality of the Bitcoin design.We will mention some incidents when programming errors lead to forks that needed to be resolved“manually”and we will explain the transaction malleability problem.We will then present more fundamental problems with the blockchain technology.In particular we will explain the self-ish mining attack introduced in the groundbreaking paper of Eyal and Sirer[6]and the difficulty raising attack of Lear Bahack[3]that exploits the way in which the miming dif-ficulty is adjusted in Bitcoin.We will also talk about the birbery attacks of[5].2.5Smart contractsOne of the most intriguing properties of Bitcoin is the pos-sibility of creating the so-called smart contracts(originally proposed in1990s by Nick Szabo).Such contracts can be viewed asfinancial agreements between a number of parties, whose implementations are enforced by the Bitcoin system. Simple examples of such agreements include the escrow and dispute mediation,and the assurance contracts.More ad-vanced types of contracts are the fair multiparty protocols, and in particular the decentralized lotteries[2,1,4].We will give an overview of this area.2.6Other cryptocurrenciesDiscouraging hardware mining.One of the problems of Bitcoin is that mining in hardware is much more efficient than mining in software,and hence it is completely infeasi-ble nowadays to be a miner without investing in specialized hardware.We will describe the Litecoin,which is a cur-rency that was supposed to have the property that it is not economical to mine in hardware.Less“wasteful”cryptocurrencies.Another problem with the Proofs of Work is that they require the miners to spend significant amounts of electricity on mining.There are essentially two approaches to create less“wasteful”cryp-tocurrencies.Thefirst one is to create a cryptocurrency where the work is spent on some“useful”task.We will give an overview of the currencies belonging to this class:the Permacoin,and the Primecoin.The second approach is to replace“work”by some other type of resource.This includes the Proofs of Stake,and the Proofs of Space,which is used in the recent Spacecoin proposal.We will give a short overview of these approaches.More anonymity.Since the Bitcoin’s transaction ledger is public,the only anonymity in this system comes from the fact that the users are using pseudonyms,instead if their real names.As recently shown in[7]this does not provide sufficient privacy protection.We will briefly talk about this result,and then we will explain(on a high level)the main design principles of Zerocash,which is a new proposal for a currency that provides true anonymity.2.7Research directionsWe will conclude with an overview of the open research problems in this area,like the need for better understand-ing of the Bitcoin security model,and improvement of the blockchain technology.We will also mention the open prob-lems concerning the distributed contracts,in particular we will discuss what obstacles need to be overcome to make them really practical.Finally,we will also describe the problems with securely storing the Bitcoin secret keys(in the so-called wallets).3.REFERENCES[1]M.Andrychowicz,S.Dziembowski,D.Malinowski,and L.Mazurek.Fair two-party computations viaBitcoin deposits.In BITCOIN workshop in association with the Financial Cryptography and Data Securityconference,2014.[2]M.Andrychowicz,S.Dziembowski,D.Malinowski,and L.Mazurek.Secure multiparty computations onBitcoin.In2014IEEE Symposium on Security andPrivacy[3]L.Bahack.Theoretical bitcoin attacks with less thanhalf of the computational power.arXiv,2013.[4]I.Bentov and R.Kumaresan.How to use bitcoin todesign fair protocols.In CRYPTO2014[5]J.Bonneau,E.W.Felten,S.Goldfeder,J.A.Kroll,and A.Narayanan.Why buy when you can rent?Bribery attacks on Bitcoin consensus,November2014.manuscript[6]I.Eyal and E.G¨u n Sirer.Majority is not enough:Bitcoin mining is vulnerable.In FinancialCryptography and Data Security,2014.[7]S.Meiklejohn,M.Pomarole,G.Jordan,K.Levchenko,D.McCoy,G.M.Voelker,and S.Savage.Afistful ofbitcoins:Characterizing payments among men withno names.In Proceedings of the2013Conference onInternet Measurement Conference.[8]ler,E.Shi,A.Kosba,and J.Katz.Preprint:Nonoutsourceable scratch-offpuzzles to discouragebitcoin mining coalitions.2015.[9]Satoshi Nakamoto.Bitcoin:A peer-to-peer electroniccash system,2008.2.2Bitcoin main design principles。

crypto++例子Crypto++（也被称为CryptoPP）是一个C++库，提供了大量的加密和解密算法。

以下是一个使用Crypto++库进行AES加密和解密的简单示例：首先，你需要安装Crypto++库。

你可以从其官方网站下载源代码并编译安装，或者使用包管理器如apt或brew进行安装。

下面是一个使用Crypto++库进行AES加密和解密的C++代码示例：cpp复制代码：#include <iostream>#include <string>#include <cryptopp/aes.h>#include <cryptopp/modes.h>#include <cryptopp/filters.h>#include <cryptopp/hex.h>int main() {// 密钥和初始化向量std::string key = "0123456789abcdef"; // 16字节密钥std::string iv = "abcdef0123456789"; // 16字节初始化向量// 待加密的数据std::string plaintext = "Hello, world!";try {// 创建AES对象，设置密钥和初始化向量CryptoPP::AES::Encryption aesEncryption(key.c_str(), CryptoPP::AES::DEFAULT_KEYLENGTH);CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption, iv.c_str());// 加密数据std::string ciphertext;CryptoPP::StreamTransformationFilterstfEncryptor(cbcEncryption, new CryptoPP::StringSink(ciphertext));stfEncryptor.Put(reinterpret_cast<const unsigned char*>(plaintext.c_str()), plaintext.length() + 1);stfEncryptor.MessageEnd();// 输出加密后的数据（以十六进制形式）std::cout << "加密后的数据（十六进制形式）: " << CryptoPP::Hex::Encode(ciphertext) << std::endl;// 解密数据std::string decryptedtext;CryptoPP::StreamTransformationFilterstfDecryptor(cbcDecryption, new CryptoPP::StringSink(decryptedtext));stfDecryptor.Put(reinterpret_cast<const unsigned char*>(ciphertext.c_str()), ciphertext.length());stfDecryptor.MessageEnd();// 输出解密后的数据std::cout << "解密后的数据: " << decryptedtext << std::endl;} catch (const CryptoPP::Exception& e) {std::cerr << "加密或解密过程中发生错误: " << e.what() << std::endl;}return 0;}这个例子使用了AES算法，CBC模式，和16字节的密钥和初始化向量。

dm-crypt crypto原理
DM-Crypt是一种在Linux内核中实现磁盘加密的技术，它使用cryptographic algorithms（加密算法）来保护存储设备上的数据。

以下是DM-Crypt加密原理的简要概述：
1. 初始化阶段：当一个加密设备被挂载时，它首先需要被初始化。

这个过程包括生成一个密钥（通常是AES或其他对称加密算法），并使用它来加密存储设备上的数据。

2. 加密和解密：在加密和解密数据时，DM-Crypt使用对称加密算法（如AES）进行加密和解密操作。

加密过程使用生成的密钥对数据进行加密，使得只有拥有正确解密密钥的用户才能访问数据。

解密过程则使用相同的密钥对数据进行解密，以恢复原始数据。

3. 存储设备访问：当操作系统需要访问加密设备上的数据时，它首先需要与cryptoloop或cryptfs等驱动程序进行交互。

驱动程序会检查请求的数据是否已经被加密，并根据需要使用密钥进行解密或加密操作。

4. 密钥管理：DM-Crypt使用一个主密钥（Master Key）来管理和保护其他密钥。

主密钥通常存储在另一个加密设备上，只有拥有正确访问权限的用户才能访问它。

主密钥用于生成用于加密和解密其他设备的密钥。

总的来说，DM-Crypt通过使用对称加密算法对存储设备上的数据进行加密，并使用主密钥进行管理和保护，确保只有拥有正确访问权限的用户才能访问加密设备上的数据。

这种技术通常被用于保护重要数据的安全性和保密性。

crypto aes 用法-回复AES（Advanced Encryption Standard）是一种对称加密算法，广泛应用于保护数据的安全性。

它是美国国家标准和技术研究院（NIST）于2001年制定的，目前是最常用的加密算法之一。

AES通过将输入数据切分成固定长度的块，再使用不同的密钥对每个块进行加密和解密，从而实现数据的保护。

本文将一步一步地介绍AES算法的用法。

1. 密钥长度选择AES支持128位、192位和256位三种密钥长度。

密钥长度越长，加密强度越高，但同时也增加了计算复杂性。

一般情况下，128位密钥已经足够安全，因此我们将以128位密钥为例进行后续的操作。

2. 密钥生成在AES中，密钥是随机生成的，可以通过伪随机数生成器（PRNG）来产生。

为了确保密钥的随机性和安全性，最好使用专门设计的密码学安全PRNG。

一个常用的方法是使用操作系统提供的随机数生成器。

3. 明文的填充由于AES算法要求输入数据长度必须是128位的倍数，因此如果明文长度不足128位，需要进行填充。

常用的填充方式有PKCS#5和PKCS#7，它们在明文末尾添加了一定数量的字节来满足长度要求。

4. 初始化向量（IV）的选择IV用于增强AES算法的安全性，它与密钥一起被用于加密和解密操作。

IV 必须是唯一且不可预测的，一般情况下，IV的长度等于加密块的长度，即128位。

常见的方式是通过伪随机数生成器生成IV。

5. 密钥扩展在AES算法中，会对密钥进行扩展以生成多轮加密需要的子密钥。

扩展密钥的过程是通过对原始密钥应用一系列变换来实现的。

6. 加密在加密过程中，AES算法使用初始轮密钥对明文进行置换和替换操作，然后进行多轮的轮函数操作，每轮的子密钥都与明文进行异或运算。

最后一轮加密后的结果即为密文。

7. 解密解密过程与加密过程相似，但是子密钥的顺序是相反的。

解密操作使用的轮密钥与加密操作使用的轮密钥完全相同，只是顺序相反。

crypto解题方法一、引言密码学是一门研究保护信息安全的学科，它涉及加密算法、解密算法、数字签名等多个方面。

在CTF比赛中，crypto题目是必不可少的一部分。

本文将介绍一些常见的crypto解题方法。

二、基础知识在开始介绍解题方法之前，我们需要了解一些基础知识。

1. 常见加密算法（1）对称加密算法：DES、3DES、AES等。

（2）非对称加密算法：RSA、ECC等。

2. 常见编码方式（1）Base64编码：将二进制数据转换为可打印字符。

（2）Hex编码：将二进制数据转换为十六进制表示的字符串。

3. 常见攻击方式（1）暴力破解：尝试所有可能的密钥或密码，直到找到正确的为止。

（2）字典攻击：使用预先准备好的字典进行破解。

三、常见crypto题目类型及解题方法1. Base64/Hex编码Base64和Hex编码是常见的数据表示方式，在CTF比赛中也经常被用来隐藏信息。

我们可以通过相应的解码工具将其还原为原始数据，并进行后续分析。

2. 对称加密算法对称加密算法的加密和解密使用相同的密钥，因此在解题时需要找到正确的密钥。

常见的对称加密算法有DES、3DES、AES等。

（1）暴力破解如果我们无法获取正确的密钥，可以尝试使用暴力破解的方式进行破解。

这种方法需要耗费大量时间和计算资源，因此只适用于较简单的加密算法。

（2）字典攻击字典攻击是一种更为高效的破解方法，它利用预先准备好的字典进行猜测。

在CTF比赛中，我们可以根据题目给出的提示或者上下文信息来构建字典，提高破解成功率。

3. 非对称加密算法非对称加密算法包括公钥加密和数字签名两个方面。

常见的非对称加密算法有RSA、ECC等。

（1）公钥加密公钥加密是一种将信息通过公钥进行加密，再通过私钥进行解密的方式。

在CTF比赛中，我们通常需要找到正确的私钥才能进行解题。

如果我们能够获取到公钥和明文信息，则可以使用在线工具或脚本进行尝试。

如果无法获取到公钥，则可以根据题目给出的提示或者上下文信息进行猜测。