purr-c/encrypt.c

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>
#include <sys/random.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>

#include "libbaseencode/baseencode.h"

#include "purr.h"
#include "mmap_file.h"

/*
 * This function takes an mmap_file struct, and creates an encrypted buffer from it.
 * The created file is passed to an atexit function so it can be deleted automatically.
 * Args:
 *   file: mmap_file for the input file
 *   keyp: will receive the newly generated random key
 *   ivp: will receive the newly generated random IV (if enabled in purr.h)
 */
struct mmap_file encrypt_mmap(struct mmap_file file, uint8_t **keyp, uint8_t **ivp)
{
    off_t file_size = file.size;
    ssize_t blocks = file_size / br_aes_big_BLOCK_SIZE;
    if (blocks * br_aes_big_BLOCK_SIZE < file_size) blocks++;
    file_size = blocks * br_aes_big_BLOCK_SIZE;

    struct mmap_file rv = {.size = file_size, .prot = PROT_MEM, .flags = MAP_MEM};

    uint8_t *key = calloc(KEY_LEN, 1);
    uint8_t *iv = calloc(IV_LEN, 1);
    uint8_t *iv_throwaway = calloc(IV_LEN, 1);
    if (key == NULL || iv == NULL || iv_throwaway == NULL) {
        perror("allocation failure");
        return rv;
    }

    ssize_t err = getrandom(key, KEY_LEN, 0);
    //ssize_t err = KEY_LEN;
    if (err != KEY_LEN) {
        fputs("getrandom() error!\n", stderr);
        return rv;
    }
    #ifdef RANDOMIZE_IV
    err = getrandom(iv, IV_LEN, 0);
    memcpy(iv_throwaway, iv, IV_LEN);
    if (err != IV_LEN) {
        fputs("getrandom() error!\n", stderr);
        return rv;
    }
    #endif /* RANDOMIZE_IV */

    rv.data = mmap(NULL, rv.size, rv.prot, rv.flags, -1, 0);
    if (ERROR_MMAP(rv)) {
        perror("mmap()");
        return rv;
    }

    memcpy(rv.data, file.data, file.size);
    ssize_t i = 0;
    for (; i < (file_size - file.size); i++) {
        rv.data[file.size + i] = file.data[file.size + i];
    }
    // anonymous mapping -> subsequent padding bytes are already zero

    br_aes_big_cbcenc_keys br = { 0 };
    br_aes_big_cbcenc_init(&br, key, KEY_LEN);
    br_aes_big_cbcenc_run(&br, iv_throwaway, rv.data, file_size);
    free(iv_throwaway);

    #ifdef ENCODE_BASE_64
    baseencode_error_t berr;
    char *data = base64_encode(rv.data, rv.size, &berr);
    if (data == NULL) {
        fprintf(stderr, "base64_encode(): error code %d\n", berr);
        // TODO: returns good rv
        return rv;
    }
    size_t len = strlen(data);
    struct mmap_file rv_64 = {.size = len, .prot = PROT_MEM, .flags = MAP_MEM};
    rv_64.data = mmap(NULL, rv_64.size, rv_64.prot, rv_64.flags, -1, 0);
    if (ERROR_MMAP(rv_64)) {
        perror("mmap()");
        // TODO: returns good rv
        return rv;
    }
    memcpy(rv_64.data, data, len);

    free(data);
    munmap(rv.data, rv.size);
    rv = rv_64;
    #endif /* ENCODE_BASE_64 */

    munmap(file.data, file.size);

    // pass pointers to caller
    *keyp  = key;
    *ivp = iv;

    return rv;
}

struct mmap_file decrypt_mmap(struct mmap_file file, const uint8_t *key, const uint8_t *iv)
{
    struct mmap_file rv = {.size = file.size, .prot = PROT_MEM, .flags = MAP_MEM};

    #ifdef DECODE_BASE_64
    baseencode_error_t berr;
    size_t data_len;
    // TODO: find out why file.size is weird
    uint8_t *data = base64_decode((char *)file.data, strlen((char *)file.data), &berr, &data_len);
    if (data == NULL) {
        fprintf(stderr, "base64_decode(): error code %d\n", berr);
        return rv;
    }
    // big hack to bypass issues
    //assert(data_len % br_aes_big_BLOCK_SIZE == 0);
    data_len -= data_len % br_aes_big_BLOCK_SIZE;

    rv.size = data_len;
    #endif /* DECODE_BASE_64 */


    rv.data = mmap(NULL, rv.size, rv.prot, rv.flags, -1, 0);
    if (ERROR_MMAP(rv)) {
        perror("mmap()");
        return rv;
    }

    #ifdef DECODE_BASE_64
    memcpy(rv.data, data, rv.size);
    free(data);
    #else
    memcpy(rv.data, file.data, file.size);
    #endif /* DECODE_BASE_64 */

    munmap(file.data, file.size);

    uint8_t *iv_throwaway = calloc(IV_LEN, 1);
    if (iv_throwaway == NULL) {
        perror("malloc()");
        // TODO: returns good rv
        return rv;
    }
    memcpy(iv_throwaway, iv, IV_LEN);

    br_aes_big_cbcdec_keys br = { 0 };
    br_aes_big_cbcdec_init(&br, key, KEY_LEN);
    br_aes_big_cbcdec_run(&br, iv_throwaway, rv.data, rv.size);
    free(iv_throwaway);

    // kinda hacky, but not sure how to determine where padding starts otherwise
    // TODO: look only at last block, perhaps?
    rv.size = strlen((char *)rv.data);

    return rv;
}