path: root/src/crypt.c

// Optional encryption support.
// Mohsin Ahmed, mosh@sasi.com, 98-09-24
// Based on zip/crypt sources.
//
// NOTE FOR USA: Since 2000 exporting this code from the USA is allowed to
// most countries. There are a few exceptions, but that still should not be a
// problem since this code was originally created in Europe and India.
//
// Blowfish addition originally made by Mohsin Ahmed,
// http://www.cs.albany.edu/~mosh 2010-03-14
// Based on blowfish by Bruce Schneier (http://www.schneier.com/blowfish.html)
// and sha256 by Christophe Devine.

#include "vim.h"
#include "misc2.h"
#include "blowfish.h"
#include "ex_getln.h"
#include "message.h"
#include "option.h"

static void make_crc_tab(void);

static unsigned long crc_32_tab[256];

// Fills the CRC table.
static void make_crc_tab(void)
{
  unsigned long s;
  unsigned long t;
  unsigned long v;
  static bool done = false;

  if (done) {
    return;
  }

  for (t = 0; t < 256; t++) {
    v = t;

    for (s = 0; s < 8; s++) {
      v = (v >> 1) ^ ((v & 1) * (unsigned long)0xedb88320L);
    }
    crc_32_tab[t] = v;
  }
  done = true;
}

#define CRC32(c, b) (crc_32_tab[((int)(c) ^ (b)) & 0xff] ^ ((c) >> 8))

static unsigned long keys[3]; // keys defining the pseudo-random sequence

// Returns the next byte in the pseudo-random sequence.
#define DECRYPT_BYTE_ZIP(t) { \
  unsigned short temp; \
  temp = (unsigned short)keys[2] | 2; \
  t = (int)(((unsigned)(temp * (temp ^ 1U)) >> 8) & 0xff); \
}

// Updates the encryption keys with the next byte of plain text.
#define UPDATE_KEYS_ZIP(c) { \
  keys[0] = CRC32(keys[0], (c)); \
  keys[1] += keys[0] & 0xff; \
  keys[1] = keys[1] * 134775813L + 1; \
  keys[2] = CRC32(keys[2], (int)(keys[1] >> 24)); \
}

static int crypt_busy = 0;
static unsigned long saved_keys[3];
static int saved_crypt_method;

// Returns int value for crypt method string:
// 0 for "zip", the old method. Also for any non-valid value.
// 1 for "blowfish".
int crypt_method_from_string(char_u *s)
{
  return *s == 'b' ? 1 : 0;
}

// Returns the crypt method for buffer "buf" as a number.
int get_crypt_method(buf_T *buf)
{
  return crypt_method_from_string(*buf->b_p_cm == NUL ? p_cm : buf->b_p_cm);
}

// Sets the crypt method for buffer "buf" to "method" using the int value as
// returned by crypt_method_from_string().
void set_crypt_method(buf_T *buf, int method)
{
  free_string_option(buf->b_p_cm);
  buf->b_p_cm = vim_strsave((char_u *)(method == 0 ? "zip" : "blowfish"));
}

// Prepares for initializing the encryption. If already doing encryption then
// save the state.
// Must always be called symmetrically with crypt_pop_state().
void crypt_push_state(void)
{
  if (crypt_busy == 1) {
    // Save the state
    if (use_crypt_method == 0) {
      saved_keys[0] = keys[0];
      saved_keys[1] = keys[1];
      saved_keys[2] = keys[2];
    } else {
      bf_crypt_save();
    }
    saved_crypt_method = use_crypt_method;
  } else if (crypt_busy > 1) {
    EMSG2(_(e_intern2), "crypt_push_state()");
  }
  crypt_busy++;
}

// Ends encryption. If doing encryption before crypt_push_state() then restore
// the saved state.
// Must always be called symmetrically with crypt_push_state().
void crypt_pop_state(void)
{
  crypt_busy--;

  if (crypt_busy == 1) {
    use_crypt_method = saved_crypt_method;

    if (use_crypt_method == 0) {
      keys[0] = saved_keys[0];
      keys[1] = saved_keys[1];
      keys[2] = saved_keys[2];
    } else {
      bf_crypt_restore();
    }
  }
}

// Encrypts "from[len]" into "to[len]".
// "from" and "to" can be equal to encrypt in place.
void crypt_encode(char_u *from, size_t len, char_u *to)
{
  size_t i;
  int ztemp;
  int t;

  if (use_crypt_method == 0) {
    for (i = 0; i < len; i++) {
      ztemp = from[i];
      DECRYPT_BYTE_ZIP(t);
      UPDATE_KEYS_ZIP(ztemp);
      to[i] = t ^ ztemp;
    }
  } else {
    bf_crypt_encode(from, len, to);
  }
}

// Decrypts "ptr[len]" in place.
void crypt_decode(char_u *ptr, long len)
{
  char_u *p;

  if (use_crypt_method == 0) {
    for (p = ptr; p < ptr + len; p++) {
      unsigned short temp;

      temp = (unsigned short)keys[2] | 2;
      temp = (int)(((unsigned)(temp * (temp ^ 1U)) >> 8) & 0xff);
      UPDATE_KEYS_ZIP(*p ^= temp);
    }
  } else {
    bf_crypt_decode(ptr, len);
  }
}

// Initializes the encryption keys and the random header according to
// the given password.
// If "passwd" is NULL or empty, don't do anything.
// in: "passwd" password string with which to modify keys
void crypt_init_keys(char_u *passwd)
{
  if ((passwd != NULL) && (*passwd != NUL)) {
    if (use_crypt_method == 0) {
      char_u *p;

      make_crc_tab();
      keys[0] = 305419896L;
      keys[1] = 591751049L;
      keys[2] = 878082192L;

      for (p = passwd; *p != NUL; p++) {
        UPDATE_KEYS_ZIP((int)*p);
      }
    } else {
      bf_crypt_init_keys(passwd);
    }
  }
}

// Frees an allocated crypt key. Clears the text to make sure it doesn't stay
// in memory anywhere.
void free_crypt_key(char_u *key)
{
  char_u *p;

  if (key != NULL) {
    for (p = key; *p != NUL; p++) {
      *p = 0;
    }
    free(key);
  }
}

// Asks the user for a crypt key.
// When "store" is TRUE, the new key is stored in the 'key' option, and the
// 'key' option value is returned: Don't free it.
// When "store" is FALSE, the typed key is returned in allocated memory.
// in: "twice" Ask for the key twice.
// Returns NULL on failure.
char_u *get_crypt_key(int store, int twice)
{
  char_u *p1;
  char_u *p2 = NULL;
  int round;

  for (round = 0;; round++) {
    cmdline_star = TRUE;
    cmdline_row = msg_row;
    char_u *prompt = (round == 0)
        ? (char_u *) _("Enter encryption key: ")
        : (char_u *) _("Enter same key again: ");
    p1 = getcmdline_prompt(NUL, prompt, 0, EXPAND_NOTHING, NULL);
    cmdline_star = FALSE;
    if (p1 == NULL) {
      break;
    }

    if (round == twice) {
      if ((p2 != NULL) && (STRCMP(p1, p2) != 0)) {
        MSG(_("Keys don't match!"));
        free_crypt_key(p1);
        free_crypt_key(p2);
        p2 = NULL;
        round = -1; // Do it again
        continue;
      }

      if (store) {
        set_option_value((char_u *) "key", 0L, p1, OPT_LOCAL);
        free_crypt_key(p1);
        p1 = curbuf->b_p_key;
      }
      break;
    }
    p2 = p1;
  }

  // Since the user typed this, no need to wait for return.
  if (msg_didout) {
    msg_putchar('\n');
  }
  need_wait_return = FALSE;
  msg_didout = FALSE;

  free_crypt_key(p2);
  return p1;
}