keygrip-from-gnupg-sexp-key-file-via-libgcrypt.c

// gcc -lgcrypt ...

#include <assert.h>
#include <gcrypt.h>
#include <stdio.h>
#include <stdlib.h>

const size_t KEYGRIP_LENGTH = 20;

unsigned char* read_binary(const char* path, size_t* bytes_read) {
    FILE* f = fopen(path, "rb");
    fseek(f, 0, SEEK_END);
    size_t size = ftell(f);
    fseek(f, 0, SEEK_SET);
    unsigned char* data = malloc(sizeof(unsigned char) * size);
    assert(data != NULL);
    *bytes_read = fread(data, sizeof(char), size, f);
    assert(*bytes_read == sizeof(char)*size);
    fclose(f);
    return data;
}

gcry_sexp_t load_sexp_from_file(const char* path) {
    size_t size;
    char* data = read_binary(path, &size);
    assert(data != NULL && size > 0);
    gcry_sexp_t key;
    gcry_error_t err = gcry_sexp_new(&key, data, size, 0);
    if(err) {
        fprintf(stderr, "failed load sexp: %s (%d)\n", gcry_strerror(err), gcry_err_code(err));
        return NULL;
    } else {
        return key;
    }
}

void dump_keygrip(gcry_sexp_t key) {
    unsigned char* keygrip = gcry_pk_get_keygrip(key, NULL);
    assert(keygrip != NULL);
    for(int i=0; i<KEYGRIP_LENGTH; i++) {
        printf("%X", keygrip[i]);
    }
    printf("\n");
    free(keygrip);
}

int main(int argc, const char* argv[]) {
    if(!gcry_check_version(GCRYPT_VERSION)) {
        fprintf(stderr, "gcrypt version mismatch");
        return 1;
    }
    gcry_sexp_t key = load_sexp_from_file(argv[1]);
    assert(key != NULL);
    // gcry_sexp_dump(key);
    dump_keygrip(key);
    gcry_sexp_release(key);
    return 0;
}