为了将AES加密文本作为std::istream提供给解析器组件，我尝试创建一个包含vanilla crypto ++加密/解密的std::streambuf实现。
main()函数调用以下函数来比较我的包装器和vanilla实现：
EncryptFile() - 使用我的streambuf实现加密文件DecryptFile() - 使用我的streambuf实现解密文件EncryptFileVanilla() - 使用vanilla crypto ++加密文件DecryptFileVanilla() - 使用vanilla crypto ++解密文件问题在于EncryptFile()和EncryptFileVanilla()创建的加密文件完全相同。由DecryptFile()创建的解密文件不正确，比DecryptFileVanilla()创建的文件短16个字节。可能并非巧合的是，块大小也是16。
我认为这个问题必须在CryptStreamBuffer::GetNextChar()，但我一直在盯着它和加密++文档几个小时。
有人可以帮忙解释吗？
关于我的std::streambuf实施方式有多么糟糕或幼稚的任何其他评论也欢迎; - ）
谢谢，
汤姆
// Runtime Includes
#include <iostream>
// Crypto++ Includes
#include "aes.h"
#include "modes.h" // xxx_Mode< >
#include "filters.h" // StringSource and
// StreamTransformation
#include "files.h"
using namespace std;
class CryptStreamBuffer: public std::streambuf {
public:
CryptStreamBuffer(istream& encryptedInput, CryptoPP::StreamTransformation& c);
CryptStreamBuffer(ostream& encryptedOutput, CryptoPP::StreamTransformation& c);
~CryptStreamBuffer();
protected:
virtual int_type overflow(int_type ch = traits_type::eof());
virtual int_type uflow();
virtual int_type underflow();
virtual int_type pbackfail(int_type ch);
virtual int sync();
private:
int GetNextChar();
int m_NextChar; // Buffered character
CryptoPP::StreamTransformationFilter* m_StreamTransformationFilter;
CryptoPP::FileSource* m_Source;
CryptoPP::FileSink* m_Sink;
}; // class CryptStreamBuffer
CryptStreamBuffer::CryptStreamBuffer(istream& encryptedInput, CryptoPP::StreamTransformation& c) :
m_NextChar(traits_type::eof()),
m_StreamTransformationFilter(0),
m_Source(0),
m_Sink(0) {
m_StreamTransformationFilter = new CryptoPP::StreamTransformationFilter(c, 0, CryptoPP::BlockPaddingSchemeDef::PKCS_PADDING);
m_Source = new CryptoPP::FileSource(encryptedInput, false, m_StreamTransformationFilter);
}
CryptStreamBuffer::CryptStreamBuffer(ostream& encryptedOutput, CryptoPP::StreamTransformation& c) :
m_NextChar(traits_type::eof()),
m_StreamTransformationFilter(0),
m_Source(0),
m_Sink(0) {
m_Sink = new CryptoPP::FileSink(encryptedOutput);
m_StreamTransformationFilter = new CryptoPP::StreamTransformationFilter(c, m_Sink, CryptoPP::BlockPaddingSchemeDef::PKCS_PADDING);
}
CryptStreamBuffer::~CryptStreamBuffer() {
if (m_Sink) {
delete m_StreamTransformationFilter;
// m_StreamTransformationFilter owns and deletes m_Sink.
}
if (m_Source) {
delete m_Source;
// m_Source owns and deletes m_StreamTransformationFilter.
}
}
CryptStreamBuffer::int_type CryptStreamBuffer::overflow(int_type ch) {
return m_StreamTransformationFilter->Put((byte)ch);
}
CryptStreamBuffer::int_type CryptStreamBuffer::uflow() {
int_type result = GetNextChar();
// Reset the buffered character
m_NextChar = traits_type::eof();
return result;
}
CryptStreamBuffer::int_type CryptStreamBuffer::underflow() {
return GetNextChar();
}
CryptStreamBuffer::int_type CryptStreamBuffer::pbackfail(int_type ch) {
return traits_type::eof();
}
int CryptStreamBuffer::sync() {
// TODO: Not sure sync is the correct place to be doing this.
// Should it be in the destructor?
if (m_Sink) {
m_StreamTransformationFilter->MessageEnd();
// m_StreamTransformationFilter->Flush(true);
}
return 0;
}
int CryptStreamBuffer::GetNextChar() {
// If we have a buffered character do nothing
if (m_NextChar != traits_type::eof()) {
return m_NextChar;
}
// If there are no more bytes currently available then pump the source
if (m_StreamTransformationFilter->MaxRetrievable() == 0) {
m_Source->Pump(1024);
}
// Retrieve the next byte
byte nextByte;
size_t noBytes = m_StreamTransformationFilter->Get(nextByte);
if (0 == noBytes) {
return traits_type::eof();
}
// Buffer up the next character
m_NextChar = nextByte;
return m_NextChar;
}
void InitKey(byte key[]) {
key[0] = -62;
key[1] = 102;
key[2] = 78;
key[3] = 75;
key[4] = -96;
key[5] = 125;
key[6] = 66;
key[7] = 125;
key[8] = -95;
key[9] = -66;
key[10] = 114;
key[11] = 22;
key[12] = 48;
key[13] = 111;
key[14] = -51;
key[15] = 112;
}
/** Decrypt using my CryptStreamBuffer */
void DecryptFile(const char* sourceFileName, const char* destFileName) {
ifstream ifs(sourceFileName, ios::in | ios::binary);
ofstream ofs(destFileName, ios::out | ios::binary);
byte key[CryptoPP::AES::DEFAULT_KEYLENGTH];
InitKey(key);
CryptoPP::ECB_Mode<CryptoPP::AES>::Decryption decryptor(key, sizeof(key));
if (ifs) {
if (ofs) {
CryptStreamBuffer cryptBuf(ifs, decryptor);
std::istream decrypt(&cryptBuf);
int c;
while (EOF != (c = decrypt.get())) {
ofs << (char)c;
}
ofs.flush();
}
else {
std::cerr << "Failed to open file '" << destFileName << "'." << endl;
}
}
else {
std::cerr << "Failed to open file '" << sourceFileName << "'." << endl;
}
}
/** Encrypt using my CryptStreamBuffer */
void EncryptFile(const char* sourceFileName, const char* destFileName) {
ifstream ifs(sourceFileName, ios::in | ios::binary);
ofstream ofs(destFileName, ios::out | ios::binary);
byte key[CryptoPP::AES::DEFAULT_KEYLENGTH];
InitKey(key);
CryptoPP::ECB_Mode<CryptoPP::AES>::Encryption encryptor(key, sizeof(key));
if (ifs) {
if (ofs) {
CryptStreamBuffer cryptBuf(ofs, encryptor);
std::ostream encrypt(&cryptBuf);
int c;
while (EOF != (c = ifs.get())) {
encrypt << (char)c;
}
encrypt.flush();
}
else {
std::cerr << "Failed to open file '" << destFileName << "'." << endl;
}
}
else {
std::cerr << "Failed to open file '" << sourceFileName << "'." << endl;
}
}
/** Decrypt using vanilla crypto++ */
void DecryptFileVanilla(const char* sourceFileName, const char* destFileName) {
byte key[CryptoPP::AES::DEFAULT_KEYLENGTH];
InitKey(key);
CryptoPP::ECB_Mode<CryptoPP::AES>::Decryption decryptor(key, sizeof(key));
CryptoPP::FileSource(sourceFileName, true,
new CryptoPP::StreamTransformationFilter(decryptor,
new CryptoPP::FileSink(destFileName), CryptoPP::BlockPaddingSchemeDef::PKCS_PADDING
) // StreamTransformationFilter
); // FileSource
}
/** Encrypt using vanilla crypto++ */
void EncryptFileVanilla(const char* sourceFileName, const char* destFileName) {
byte key[CryptoPP::AES::DEFAULT_KEYLENGTH];
InitKey(key);
CryptoPP::ECB_Mode<CryptoPP::AES>::Encryption encryptor(key, sizeof(key));
CryptoPP::FileSource(sourceFileName, true,
new CryptoPP::StreamTransformationFilter(encryptor,
new CryptoPP::FileSink(destFileName), CryptoPP::BlockPaddingSchemeDef::PKCS_PADDING
) // StreamTransformationFilter
); // FileSource
}
int main(int argc, char* argv[])
{
EncryptFile(argv[1], "encrypted.out");
DecryptFile("encrypted.out", "decrypted.out");
EncryptFileVanilla(argv[1], "encrypted_vanilla.out");
DecryptFileVanilla("encrypted_vanilla.out", "decrypted_vanilla.out");
return 0;
}
答案 0 :(得分：5)
使用crypto ++的调试版本后，结果发现缺少的是对StreamTransformationFilter的调用，告知它不会再有来自Source的内容，它应该包含最后几个字节的处理，包括填充。
在CryptStreamBuffer::GetNextChar()：
替换：
// If there are no more bytes currently available then pump the source
if (m_StreamTransformationFilter->MaxRetrievable() == 0) {
m_Source->Pump(1024);
}
使用：
// If there are no more bytes currently available from the filter then
// pump the source.
if (m_StreamTransformationFilter->MaxRetrievable() == 0) {
if (0 == m_Source->Pump(1024)) {
// This seems to be required to ensure the final bytes are readable
// from the filter.
m_StreamTransformationFilter->ChannelMessageEnd(CryptoPP::DEFAULT_CHANNEL);
}
}
我没有声称这是最好的解决方案，只是我通过反复试验发现出现才能工作。
答案 1 :(得分：3)
如果输入缓冲区不是16字节块的多重性，则需要用虚拟字节填充最后一个块。如果最后一个块小于16个字节，则由crypto ++删除并且不加密。解密时，需要截断虚拟字节。 你指的那种'另一种方式'，已经为你做了添加和截断。 那么什么应该是虚拟字节，知道它们中有多少，因此应该被截断？我使用以下模式：用虚拟计数值填充每个字节。
示例：您需要添加8个字节吗？将它们设置为0x08,0x08,0x08,0x08,0x08,0x08,0x08,0x08。你需要添加3个字节？将它们设置为0x03,0x03,0x03等。
解密时，获取输出缓冲区的最后一个字节的值。假设它是N.检查，如果最后N个字节的值等于N.截断，如果为真。
<强>更新
CryptStreamBuffer::CryptStreamBuffer(istream& encryptedInput, CryptoPP::StreamTransformation& c) :
m_NextChar(traits_type::eof()),
m_StreamTransformationFilter(0),
m_Source(0),
m_Sink(0) {
m_StreamTransformationFilter = new CryptoPP::StreamTransformationFilter(c, 0, CryptoPP::BlockPaddingSchemeDef::ZEROS_PADDING);
m_Source = new CryptoPP::FileSource(encryptedInput, false, m_StreamTransformationFilter);
}
CryptStreamBuffer::CryptStreamBuffer(ostream& encryptedOutput, CryptoPP::StreamTransformation& c) :
m_NextChar(traits_type::eof()),
m_StreamTransformationFilter(0),
m_Source(0),
m_Sink(0) {
m_Sink = new CryptoPP::FileSink(encryptedOutput);
m_StreamTransformationFilter = new CryptoPP::StreamTransformationFilter(c, m_Sink, CryptoPP::BlockPaddingSchemeDef::ZEROS_PADDING);
}
设置ZEROS_PADDING使您的代码正常工作（在文本文件上测试）。但是为什么它不适用于DEFAULT_PADDING - 我还没找到原因。