PGP (Pretty Good Privacy)
PGP是一个完整的电子邮件安全软件包,包括加密、鉴别、电子签名和压缩等技术。
虽然 PGP 已被广泛使用,但 PGP 并不是因特网的正式标准。
一、加密过程。
![image-20240407090304770](https://xjelly-img-1318706121.cos.ap-beijing.myqcloud.com/content_img/image-20240407090304770.png)
发件人
md5用于实现消息完整性验证。
H=EAsk(MD5(P))
RSA私钥用于签名。
P1=P∣∣H
KM是收件人不知道的。在使用IDEA加密后用收件人的公钥加密共享密钥KM,串在后面,当收件人收到后,用私钥解开Km,就可以解开IDEA。
发送:
[{(P∣∣EAsk(MD5(P))).Z}KM∣∣EBpk(KM)]base64
发送(带时间戳):
[{(P∣∣EAsk(MD5(P)∣∣T)).Z}KM∣∣EBpk(KM)]base64
收件人
base64还原。
获得{(P∣∣EAsk(MD5(P))).Z}KM∣∣EBpk(KM)
用私钥解密获取KM。
DBsk(EBpk(KM)))=KM
用KM解开前面的消息。
DKM((P∣∣EAsk(MD5(P))).Z)KM)=(P∣∣EAsk(MD5(P))).Z
解压缩。
P∣∣EAsk(MD5(P))
验证A的签名。
EApk(EAsk(MD5(P)))=MD5(P)
验证完整性。
MD5(P′)==MD5(P)
信任并接收P。
设计思路
MD5用于做完整性验证。
签名常常签在消息摘要上,因为摘要比较短,节约加密开销。
压缩。需要做无损压缩,使收件人可以还原消息。
应用场景
电子邮件传输、远程办公:家里网络不稳定–>offline的应用场景。
二、IDEA加密算法
传承于DES,分组加密,密钥128位,明文密文64位。
密钥更长,去掉了DES的S盒,构造了白盒构件。
参考:密码学系列之:IDEA - 知乎 (zhihu.com)
IDEA加密块长度是64bits,密钥长度是128bits,是由八轮变换和半轮输出转换组合而成的。加密和解密的过程是类似的。我们看下IDEA的基本流程图:
![img](https://pic1.zhimg.com/80/v2-9310c5cb42fa0e6d18bdc52cac1b5eb4_720w.webp)
上面图中, 蓝色圆圈是XOR异或操作,绿色框是加法模数216。红色的点是乘模216 + 1,如果输入都是0(0x0000)那么将会被转换为216,如果输入是216,那么会被转换为0(0x0000)。
八轮操作之后,就是下面的半轮输出转换了,输出转换如下所示(中间两个值的交换抵消了最后一轮结束时的交换,因此没有净交换):
![img](https://pic1.zhimg.com/80/v2-8652af260c8778e803a1ecaa4a029600_720w.webp)
三、实验设计
在明文P后拼接了时间戳,然后进行签名。其余流程不变。
1.字段划分
在时间戳前添加字段名,便于分离出时间戳。
进行签名的数据:fileContent + “timestamp=” + timestampStr
进行IDEA加密的数据:fileContent + “timestamp=” + timestampStr + signature;
拼接后的数据:string combinedData = “data=” + ideaEncryptedData + “key=” + encryptedIDEAKey;
通过str.find()函数来划分字段。此处没有考虑邮件数据中出现与字段名相同字符串的情况。
2.原始文件
msg_file是使用命令行生成的一个.dat文件,大小为1G,内容不详,仅用于测试。
3.结果验证
Bob成功验证签名时输出Verified signature on message,并保存解密后的文件为received_file。
Bob可以成功还原Alice发送的文件。在Linux上测试时可以使用diff命令查看msg_file和received_file,输入diff命令后无输出。在Windows上测试时可以在命令提示符窗口中使用fc命令查看msg_file和received_file,输出无差异。
Alice在开始加密前输出时间戳,Bob解密后应该提取出相同的时间戳。
4.密钥管理
假设Alice和Bob在本地存有自己的私钥和双方的公钥。本实验中没有涉及RSA密钥分发。
在使用IDEA加密时,初始化向量iv采用硬编码的形式写在双方的代码里,我们认为Alice和Bob已经协商过或通过某种公开渠道知晓iv。
四、代码实现
使用C++和Crypto++库实现。
生成密钥:
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| #include "idea.h" #include "gzip.h" #include <iostream> #include <string> #include <fstream> #include <ctime> using namespace CryptoPP; using namespace std;
int main(int argc, char* argv[]) { AutoSeededRandomPool prng;
InvertibleRSAFunction params_A; params_A.GenerateRandomWithKeySize(prng, 2048); RSA::PrivateKey privateKey_A(params_A); RSA::PublicKey publicKey_A(params_A); FileSink privateKeyFile("private_A.key"); privateKey_A.Save(privateKeyFile); FileSink publicKeyFile("public_A.key"); publicKey_A.Save(publicKeyFile); AutoSeededRandomPool prng2; InvertibleRSAFunction params_B; params_B.GenerateRandomWithKeySize(prng2, 2048); RSA::PrivateKey privateKey_B(params_B); RSA::PublicKey publicKey_B(params_B); FileSink privateKeyFile_B("private_B.key"); privateKey_B.Save(privateKeyFile_B); FileSink publicKeyFile_B("public_B.key"); publicKey_B.Save(publicKeyFile_B);
return 0;
}
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加密
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| #include "cryptlib.h" #include "rijndael.h" #include "modes.h" #include "files.h" #include "osrng.h" #include "hex.h" #include "rsa.h" #include "pssr.h" #include "md5.h" #include "base64.h" #include "zlib.h" #include "idea.h" #include "gzip.h" #include <iostream> #include <string> #include <fstream> #include <ctime> using namespace CryptoPP; using namespace std;
int main(int argc, char* argv[]) {
RSA::PrivateKey privateKey_A; FileSource privateKeyFile_A("./private_A.key", true); privateKey_A.Load(privateKeyFile_A); RSA::PublicKey publicKey_A; FileSource publicKeyFile_A("./public_A.key", true); publicKey_A.Load(publicKeyFile_A); RSA::PublicKey publicKey_B; FileSource publicKeyFile_B("./public_B.key", true); publicKey_B.Load(publicKeyFile_B); AutoSeededRandomPool prng; string timestampStr = to_string(time(nullptr)); time_t timestamp = std::stoi(timestampStr); struct tm *timeinfo = std::localtime(×tamp); std::cout << "Time stamp: " << 1900 + timeinfo->tm_year << "/"; std::cout << 1 + timeinfo->tm_mon << "/"; std::cout << timeinfo->tm_mday << " "; std::cout << timeinfo->tm_hour << ":"; std::cout << timeinfo->tm_min << ":"; std::cout << timeinfo->tm_sec << std::endl; string filename = "msg_file.dat"; string fileContent; FileSource file(filename.c_str(), true, new StringSink(fileContent)); ofstream fout; fout.open("msg_file_timestamp.dat"); fout << fileContent << "timestamp=" << timestampStr; fout.close(); string signature; RSASS<PSS, MD5>::Signer signer(privateKey_A); FileSource("msg_file_timestamp.dat", true, new SignerFilter(prng, signer, new StringSink(signature))); ofstream out1; out1.open("msg_file_signatured.dat"); out1 << fileContent << "timestamp=" << timestampStr; cout<<"The size of timestampStr is "<<timestampStr.size()<<endl; out1 << signature; out1.close(); std::cout << "Message file id signatured and added timestamp successfully." << endl; FileSource fs("msg_file_signatured.dat", false); Gzip zipper(new FileSink("msg_file_zipped.gz")); fs.Attach(new Redirector(zipper)); fs.PumpAll(); byte iv[IDEA::BLOCKSIZE] = { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF }; byte key[IDEA::DEFAULT_KEYLENGTH]; prng.GenerateBlock(key, IDEA::DEFAULT_KEYLENGTH); FileSource fs2("msg_file_zipped.gz", false); IDEA::Encryption ideaEncryption(key, IDEA::DEFAULT_KEYLENGTH); CBC_Mode_ExternalCipher::Encryption cbcEncryption(ideaEncryption, iv); StreamTransformationFilter stfEncryptor(cbcEncryption, new FileSink("msg_file_zipped.gz.idea")); fs2.Attach(new Redirector(stfEncryptor)); fs2.PumpAll(); std::cout << "IDEA encryption succeeded." << endl; RSAES_OAEP_SHA_Encryptor e(publicKey_B); string encryptedIDEAKey; StringSource ss1(string((char*)key, sizeof(key)), true, new PK_EncryptorFilter(prng, e, new StringSink(encryptedIDEAKey)) ); std::cout << "IDEA key is encrypted successfully." << endl; string ideaEncryptedData; FileSource fs3("msg_file_zipped.gz.idea", true, new StringSink(ideaEncryptedData)); string combinedData = "data=" + ideaEncryptedData + "key=" + encryptedIDEAKey; string base64Data; StringSource ss2(combinedData, true, new Base64Encoder( new StringSink(base64Data) ) ); ofstream out2("encrypted_base64"); out2 << base64Data; out2.close(); std::cout << "Data and key are combined and encoded to Base64 successfully." << endl; return 0;
}
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解密
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| #include "cryptlib.h" #include "rijndael.h" #include "modes.h" #include "files.h" #include "osrng.h" #include "hex.h" #include "rsa.h" #include "pssr.h" #include "md5.h" #include "base64.h" #include "zlib.h" #include "idea.h" #include "gzip.h" #include <iostream> #include <string> #include <fstream> #include <ctime> using namespace CryptoPP; using namespace std; int main(int argc, char* argv[]) {
RSA::PrivateKey privateKey_B; FileSource privateKeyFile_B("./private_B.key", true); privateKey_B.Load(privateKeyFile_B); RSA::PublicKey publicKey_A; FileSource publicKeyFile_A("./public_A.key", true); publicKey_A.Load(publicKeyFile_A); RSA::PublicKey publicKey_B; FileSource publicKeyFile_B("./public_B.key", true); publicKey_B.Load(publicKeyFile_B); AutoSeededRandomPool prng; string base64EncodedData, decodedData; ifstream in("./encrypted_base64"); base64EncodedData = std::string(std::istreambuf_iterator<char>(in), std::istreambuf_iterator<char>()); in.close(); StringSource(base64EncodedData, true, new Base64Decoder(new StringSink(decodedData))); cout << "Base64 decoded." << endl; size_t pos = decodedData.find("key="); string encryptedIDEAData = decodedData.substr(5, pos - 5); string encryptedIDEAKey = decodedData.substr(pos + 4); cout << "IDEA key and IDEA encrypted data seperated." << endl; RSAES_OAEP_SHA_Decryptor decryptor(privateKey_B); string decryptedIDEAKey; StringSource(encryptedIDEAKey, true, new PK_DecryptorFilter(prng, decryptor, new StringSink(decryptedIDEAKey))); SecByteBlock key((const byte*)decryptedIDEAKey.data(), decryptedIDEAKey.size()); byte iv[IDEA::BLOCKSIZE] = { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF }; string decryptedData; IDEA::Decryption ideaDecryption(key, IDEA::DEFAULT_KEYLENGTH); CBC_Mode_ExternalCipher::Decryption cbcDecryption(ideaDecryption, iv); StringSource(encryptedIDEAData, true, new StreamTransformationFilter(cbcDecryption, new StringSink(decryptedData))); cout << "IDEA decrypted." << endl; string unzipped_content; Gunzip unzipper(new StringSink(unzipped_content)); unzipper.Put((unsigned char*)decryptedData.data(), decryptedData.size()); unzipper.MessageEnd(); cout << "Unzipped." << endl; int pos_tm = unzipped_content.find("timestamp="); string received_time_stamp = unzipped_content.substr(pos_tm + 10, 10); RSASS<PSS, MD5>::Verifier verifier(publicKey_A); StringSource ss2(unzipped_content, true, new SignatureVerificationFilter( verifier, NULL, SignatureVerificationFilter::THROW_EXCEPTION ) ); cout << "Verified signature on message" << endl; ofstream out("received_file"); if (out.is_open()) { out << unzipped_content.substr(0, pos_tm); out.close(); cout << "Received file is saved." << endl; } else { std::cerr << "error when opening the file." << endl; } time_t timestamp_recover = std::stoi(received_time_stamp); struct tm *timeinfo = std::localtime(×tamp_recover); cout << "Time stamp: " << 1900 + timeinfo->tm_year << "/"; cout << 1 + timeinfo->tm_mon << "/"; cout << timeinfo->tm_mday << " "; cout << timeinfo->tm_hour << ":"; cout << timeinfo->tm_min << ":"; cout << timeinfo->tm_sec << std::endl; return 0;
}
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发送
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| #include <iostream> #include <fstream> #include <string> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h>
#define PORT 8888
int main() { int sockfd; struct sockaddr_in serverAddr;
sockfd = socket(AF_INET, SOCK_STREAM, 0); if(sockfd < 0) { std::cerr << "Error creating socket" << std::endl; return 1; } serverAddr.sin_family = AF_INET; serverAddr.sin_port = htons(PORT); serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1"); if(connect(sockfd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) { std::cerr << "Error connecting to server" << std::endl; return 1; } std::string filename = "./encrypted_base64"; std::ifstream file(filename, std::ios::binary); if(!file) { std::cerr << "Error opening file" << std::endl; return 1; } char buffer[1024]; while(file.good()) { file.read(buffer, sizeof(buffer)); send(sockfd, buffer, file.gcount(), 0); } file.close(); close(sockfd); std::cout << "File sent successfully" << std::endl; return 0;
}
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接收
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| #include <iostream> #include <fstream> #include <string> #include <sys/socket.h> #include <netinet/in.h> #include <unistd.h>
#define PORT 8888
int main() { int sockfd, newsockfd; struct sockaddr_in serverAddr, clientAddr; socklen_t clientLen;
sockfd = socket(AF_INET, SOCK_STREAM, 0); if(sockfd < 0) { std::cerr << "Error creating socket" << std::endl; return 1; } serverAddr.sin_family = AF_INET; serverAddr.sin_port = htons(PORT); serverAddr.sin_addr.s_addr = INADDR_ANY; if(bind(sockfd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) { std::cerr << "Error binding socket" << std::endl; return 1; } listen(sockfd, 5); clientLen = sizeof(clientAddr); newsockfd = accept(sockfd, (struct sockaddr*)&clientAddr, &clientLen); if(newsockfd < 0) { std::cerr << "Error accepting connection" << std::endl; return 1; } std::string filename = "encrypted_base64"; std::ofstream file(filename, std::ios::binary); if(!file) { std::cerr << "Error creating file" << std::endl; return 1; } char buffer[1024]; int bytesRead; while((bytesRead = recv(newsockfd, buffer, sizeof(buffer), 0)) > 0) { file.write(buffer, bytesRead); } file.close(); close(newsockfd); close(sockfd); std::cout << "File received successfully" << std::endl; return 0;
}
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五、运行结果
加密
![image-20240511152911527](https://xjelly-img-1318706121.cos.ap-beijing.myqcloud.com/content_img/image-20240511152911527.png)
解密
![image-20240511152918350](https://xjelly-img-1318706121.cos.ap-beijing.myqcloud.com/content_img/image-20240511152918350.png)
![image-20240511152925902](https://xjelly-img-1318706121.cos.ap-beijing.myqcloud.com/content_img/image-20240511152925902.png)