ciphertext length is not a multiple of block size in cryptopp

Question

My program could encrypt text and save it in a file, and decrypt the cipher text after getting from the file.

But I keep on getting this error

terminate called after throwing an instance of 'CryptoPP::InvalidCiphertext'
what(): StreamTransformationFilter: ciphertext length is not a multiple of block size

While reading data from file i am getting file size as ciphertext length but content size is less what might be the wrong.

code:

std::string key = "0123456789abcdef";
std::string plaintext = "name macmilan age 24 ciy bonn country germany";
std::string ciphertext;
std::string decryptedtext;

CryptoPP::AES::Encryption aesEncryption((byte *)key.c_str(), CryptoPP::AES::DEFAULT_KEYLENGTH);
CryptoPP::ECB_Mode_ExternalCipher::Encryption cbcEncryption( aesEncryption);

CryptoPP::StreamTransformationFilter stfEncryptor(cbcEncryption, new CryptoPP::StringSink( ciphertext ) );
stfEncryptor.Put( reinterpret_cast<const unsigned char*>( plaintext.c_str() ), plaintext.length() + 1 );
stfEncryptor.MessageEnd();

CryptoPP::AES::Decryption aesDecryption((byte *)key.c_str(), CryptoPP::AES::DEFAULT_KEYLENGTH);
CryptoPP::ECB_Mode_ExternalCipher::Decryption cbcDecryption( aesDecryption);

std::cout << "ciphertext Text:"<<ciphertext.c_str()<<"length"<<ciphertext.length()<< std::endl;

FILE *ptr = fopen("temp.txt", "w");

if(ptr){
    fprintf(ptr, "%s",ciphertext.c_str());
    fclose(ptr);
    ptr = NULL;
}

ptr = fopen("temp.txt", "r");
if(ptr){
    fseek(ptr, 0, SEEK_END);
    size_t size = ftell(ptr);
    std::cout << "file size"<<size<< std::endl;
    char* temp = new char[size];
    rewind(ptr);
    fscanf(ptr,"%s",temp);
    ciphertext = temp;
    delete[] temp;
    ptr = NULL;
}

std::cout << "ciphertext Text:"<<ciphertext.c_str()<<"length"<<ciphertext.length() << std::endl;
try{
    CryptoPP::StreamTransformationFilter stfDecryptor(cbcDecryption, new CryptoPP::StringSink( decryptedtext ) );
    stfDecryptor.Put( reinterpret_cast<const unsigned char*>( ciphertext.c_str() ), ciphertext.size() );
    stfDecryptor.MessageEnd();
}
catch(CryptoPP::Exception &e)
{
    std::cout << "Decrypted Text:"<<e.what();

}
std::cout << "Decrypted Text: " << std::endl;
std::cout << decryptedtext;
std::cout << std::endl << std::endl;

system("pause");

return 0;

output:

ciphertext Text:î4¬■◄vqù┼Ä╢óΣ*₧z┐É;'!ìy─ªú√@╕╡Oh∙2♠ε\→ktáäì╘aÄδ▌length48
file size48
ciphertext Text:î4¬■◄vqù┼Ä╢óΣ*₧z┐É;'!ìy─ªú√@╕╡Oh∙2♠ε\length37
Decrypted Text:StreamTransformationFilter: ciphertext length is not a multiple o
f block sizeDecrypted Text:
name macmilan ag

Answer 1

In encryption various characters may appear including null (0). So when you write encrypted string in file you write null too. When you are retrieving encrypted value reader gets null character and assumes that string has been terminated. so it will be shorter. For resolve you have to use coding like Base64 or MD5 or open file and read in binary mode