GnuPGME: GPG C ++ Signature

Question

Has anyone written any tutorials or had any documentation on how to use GnuPGME so that I can write a function like gpgSign(std::string fileToBeSigned, std::string outPutFileName) in C ++?

Answer 1

Below is an example C with detailed comments that does what you are looking for - this is not the most direct approach, but should illustrate how to sign the file. It does not handle the choice of subscribers, but GPGME documents should help you.

You can save the file and make changes and check directly from the command line. To compile, just save as "gpgsign.c" and run gcc gpgsign.c -lgpgme -o gpgsign (NOTE: you must install libgpgme). You can then use gpgsign <input file> <output file>

 #ifdef HAVE_CONFIG_H #include <config.h> #endif #include <stdlib.h> #include <errno.h> #include <locale.h> #include <gpgme.h> #define fail_if_err(err) \ do { \ if (err) { \ fprintf (stderr, "%s:%d: %s: %s\n", \ __FILE__, __LINE__, gpgme_strsource (err), \ gpgme_strerror (err)); \ exit (1); \ } \ } \ while (0) void gpgSign(const char *fileToBeSigned, const char *outputFileName) { gpgme_ctx_t ctx; gpgme_error_t err; gpgme_data_t in, out; FILE *outputFile; int BUF_SIZE = 512; char buf[BUF_SIZE + 1]; int ret; /* Set the GPGME signature mode GPGME_SIG_MODE_NORMAL : Signature with data GPGME_SIG_MODE_CLEAR : Clear signed text GPGME_SIG_MODE_DETACH : Detached signature */ gpgme_sig_mode_t sigMode = GPGME_SIG_MODE_CLEAR; /* Begin setup of GPGME */ gpgme_check_version (NULL); setlocale (LC_ALL, ""); gpgme_set_locale (NULL, LC_CTYPE, setlocale (LC_CTYPE, NULL)); #ifndef HAVE_W32_SYSTEM gpgme_set_locale (NULL, LC_MESSAGES, setlocale (LC_MESSAGES, NULL)); #endif /* End setup of GPGME */ // Create the GPGME Context err = gpgme_new (&ctx); // Error handling fail_if_err (err); // Set the context to textmode gpgme_set_textmode (ctx, 1); // Enable ASCII armor on the context gpgme_set_armor (ctx, 1); // Create a data object pointing to the input file err = gpgme_data_new_from_file (&in, fileToBeSigned, 1); // Error handling fail_if_err (err); // Create a data object pointing to the out buffer err = gpgme_data_new (&out); // Error handling fail_if_err (err); // Sign the contents of "in" using the defined mode and place it into "out" err = gpgme_op_sign (ctx, in, out, sigMode); // Error handling fail_if_err (err); // Open the output file outputFile = fopen (outputFileName, "w+"); // Rewind the "out" data object ret = gpgme_data_seek (out, 0, SEEK_SET); // Error handling if (ret) fail_if_err (gpgme_err_code_from_errno (errno)); // Read the contents of "out" and place it into buf while ((ret = gpgme_data_read (out, buf, BUF_SIZE)) > 0) { // Write the contents of "buf" to "outputFile" fwrite (buf, ret, 1, outputFile); } // Error handling if (ret < 0) fail_if_err (gpgme_err_code_from_errno (errno)); // Close "outputFile" fclose(outputFile); // Release the "in" data object gpgme_data_release (in); // Release the "out" data object gpgme_data_release (out); // Release the context gpgme_release (ctx); } int main (int argc, char **argv) { if (argc != 3) { printf("Usage: gpgsign <input file> <output file>\n"); exit (1); } printf("Signing %s and placing the result into %s\n", argv[1], argv[2]); gpgSign(argv[1], argv[2]); return 0; } 

Answer 2

This answer probably comes too late, but if I were you, I'd rather use Keyczar , which is a high-level crypto toolkit with a simple API. Java, C ++, Python.

GPGME is still a pretty low-level IMO for those who need crypto features without overconfiguration. Of course, an expert in cryptography needs such complexity.

Personally, I try to avoid libraries that require me to configure this engine and this context in 100 lines of template code before I can do something basic ... but I'm not an expert.