Can anyone explain why my crypto++ decrypted file is 16 bytes short?
- by Tom Williams
I suspect it might be too much to hope for, but can anyone with experience with crypto++ explain why the "decrypted.out" file created by main() is 16 characters short (which probably not coincidentally is the block size)?
I think the issue must be in CryptStreamBuffer::GetNextChar(), but I've been staring at it and the crypto++ documentation for hours.
Any other comments about how crummy or naive my std::streambuf implementation are also welcome ;-) And I've just noticed I'm missing some calls to delete so you don't have to tell me about those.
Thanks,
Tom
// 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);
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);
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);
}
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() {
if (m_Sink) {
m_StreamTransformationFilter->MessageEnd();
}
}
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
// *** I SUSPECT THE PROBLEM IS HERE ***
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;
}
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;
}
}
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;
}
}
int main(int argc, char* argv[])
{
EncryptFile(argv[1], "encrypted.out");
DecryptFile("encrypted.out", "decrypted.out");
return 0;
}
