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How do I simply load a gpg key to import into a context using GPGME C++ library?

I am trying to build an application that decrypts a file using GPGME but I am struggling to understand the GPU Documentation. I've tried to search the web for examples but have yet to come across one that loads in a preexisting GPG key. The attempt I made consists of trying to create a context and loading a preexisting key into which will be used to decrypt a file based on this sample code.

I keep getting "Invalid Input" as a response error and have no idea why. I have included the code with output statements removed, but commented the output returns on them.

Update: After fixing the context, the decryption outputs success althrough the file is not properly decrypted and a key does not appear to have succesfully been added. I have provided the modified code below.

#include <gpgme.h>
#include <fcntl.h>

auto main(int argc, char** argv) -> int
{
    gpgme_ctx_t ctx;
    gpgme_error_t err;
    gpgme_check_version(NULL);
    err = gpgme_new(&ctx);                          // returns Success
    gpgme_data_t keydata;

    // ATTEMPTING TO IMPORT KEY FILE
    // returns Success
    err = gpgme_data_new_from_file(&keydata, "test.gpg", 1); 

    // ATTEMPTING TO IMPORT KEY INTO CONTEXT
    err = gpgme_op_import(ctx, keydata);            // returns Success 

    // ATTEMPTING TO CHECK RESULT
    // when accessing "imported" member, returns 0 keys imported
    gpgme_import_result_t impRes = gpgme_op_import_result(ctx); 

    // DECRYPT DATA

    gpgme_data_t fileDecrypted, fileEncrypted;

    int fdEncrypt = open("EncryptedFile.tar.gz", O_RDONLY);
    int fdDecrypt = open("DecryptedFile.tar.gz", O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);

    err = gpgme_data_new_from_fd(&fileEncrypted, fdEncrypt); // returns Success
    err = gpgme_data_new_from_fd(&fileDecrypted, fdDecrypt); // returns Success 

    gpgme_decrypt_result_t dec_result;
    // returns Success
    err = gpgme_op_decrypt_start (ctx, fileEncrypted, fileDecrypted);
    dec_result = gpgme_op_decrypt_result(ctx); // returns address location

    return 0;
}

Any input is much appreciated, thanks in advance!

abstriction
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  • The library is open source, it should be possible to find examples and other programs using that library. BTW: Since you have code that doesn't work but which you want to get to work, providing a [mcve] would improve your question's quality. – Ulrich Eckhardt Apr 18 '18 at 19:04
  • [gpgme_op_import examples on hotexamples.com](https://cpp.hotexamples.com/examples/-/-/gpgme_op_import/cpp-gpgme_op_import-function-examples.html) – milahu Nov 18 '21 at 12:39

1 Answers1

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The invalid value error appears to have come from the lack of setup associated with the context.

According to documentation, a new context needs to be created but for that to succeed a library version check must be called in order to initialize subsystems. Hence the additional lines of code should be added.

gpgme_check_version(NULL);
gpgme_new(&ctx);
Claudio
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abstriction
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