Change toxencryptsave API to never overwrite pass keys.

3 files changed, 39 insertions, 52 deletions

diff --git a/toxencryptsave/toxencryptsave.api.h b/toxencryptsave/toxencryptsave.api.h
index 61f685f8..3adf3a9d 100644
--- a/toxencryptsave/toxencryptsave.api.h
+++ b/toxencryptsave/toxencryptsave.api.h
@@ -82,8 +82,7 @@ error for key_derivation {
   NULL,
   /**
    * The crypto lib was unable to derive a key from the given passphrase,
-   * which is usually a lack of memory issue. The functions accepting keys
-   * do not produce this error.
+   * which is usually a lack of memory issue.
    */
   FAILED,
 }
@@ -192,21 +191,12 @@ class pass_Key {
    * for encryption and decryption. It is derived from a salt and the user-
    * provided password.
    *
-   * The $this structure is hidden in the implementation. It can be allocated
-   * using $new and must be deallocated using $free.
+   * The $this structure is hidden in the implementation. It can be created
+   * using $derive or $derive_with_salt and must be deallocated using $free.
    */
   struct this;
 
   /**
-   * Create a new $this. The initial value of it is indeterminate. To
-   * initialise it, use one of the derive_* functions below.
-   *
-   * In case of failure, this function returns NULL. The only failure mode at
-   * this time is memory allocation failure, so this function has no error code.
-   */
-  static this new();
-
-  /**
    * Deallocate a $this. This function behaves like free(), so NULL is an
    * acceptable argument value.
    */
@@ -227,7 +217,7 @@ class pass_Key {
    *
    * @return true on success.
    */
-  bool derive(const uint8_t[passphrase_len] passphrase)
+  static this derive(const uint8_t[passphrase_len] passphrase)
       with error for key_derivation;
 
   /**
@@ -239,7 +229,7 @@ class pass_Key {
    *
    * @return true on success.
    */
-  bool derive_with_salt(const uint8_t[passphrase_len] passphrase, const uint8_t[PASS_SALT_LENGTH] salt)
+  static this derive_with_salt(const uint8_t[passphrase_len] passphrase, const uint8_t[PASS_SALT_LENGTH] salt)
       with error for key_derivation;
 
   /**
diff --git a/toxencryptsave/toxencryptsave.c b/toxencryptsave/toxencryptsave.c
index 5640e82f..b7360b56 100644
--- a/toxencryptsave/toxencryptsave.c
+++ b/toxencryptsave/toxencryptsave.c
@@ -71,11 +71,6 @@ struct Tox_Pass_Key {
     uint8_t key[TOX_PASS_KEY_LENGTH];
 };
 
-Tox_Pass_Key *tox_pass_key_new(void)
-{
-    return (Tox_Pass_Key *)malloc(sizeof(Tox_Pass_Key));
-}
-
 void tox_pass_key_free(Tox_Pass_Key *pass_key)
 {
     free(pass_key);
@@ -123,23 +118,23 @@ bool tox_get_salt(const uint8_t *data, uint8_t *salt, TOX_ERR_GET_SALT *error)
  *
  * returns true on success
  */
-bool tox_pass_key_derive(Tox_Pass_Key *out_key, const uint8_t *passphrase, size_t pplength,
-                         TOX_ERR_KEY_DERIVATION *error)
+Tox_Pass_Key *tox_pass_key_derive(const uint8_t *passphrase, size_t pplength,
+                                  TOX_ERR_KEY_DERIVATION *error)
 {
     uint8_t salt[crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
     randombytes(salt, sizeof salt);
-    return tox_pass_key_derive_with_salt(out_key, passphrase, pplength, salt, error);
+    return tox_pass_key_derive_with_salt(passphrase, pplength, salt, error);
 }
 
 /* Same as above, except with use the given salt for deterministic key derivation.
  * The salt must be TOX_PASS_SALT_LENGTH bytes in length.
  */
-bool tox_pass_key_derive_with_salt(Tox_Pass_Key *out_key, const uint8_t *passphrase, size_t pplength,
-                                   const uint8_t *salt, TOX_ERR_KEY_DERIVATION *error)
+Tox_Pass_Key *tox_pass_key_derive_with_salt(const uint8_t *passphrase, size_t pplength,
+        const uint8_t *salt, TOX_ERR_KEY_DERIVATION *error)
 {
-    if (!salt || !out_key || (!passphrase && pplength != 0)) {
+    if (!salt || (!passphrase && pplength != 0)) {
         SET_ERROR_PARAMETER(error, TOX_ERR_KEY_DERIVATION_NULL);
-        return 0;
+        return NULL;
     }
 
     uint8_t passkey[crypto_hash_sha256_BYTES];
@@ -157,14 +152,22 @@ bool tox_pass_key_derive_with_salt(Tox_Pass_Key *out_key, const uint8_t *passphr
                 crypto_pwhash_scryptsalsa208sha256_MEMLIMIT_INTERACTIVE) != 0) {
         /* out of memory most likely */
         SET_ERROR_PARAMETER(error, TOX_ERR_KEY_DERIVATION_FAILED);
-        return 0;
+        return NULL;
     }
 
     sodium_memzero(passkey, crypto_hash_sha256_BYTES); /* wipe plaintext pw */
+
+    Tox_Pass_Key *out_key = (Tox_Pass_Key *)malloc(sizeof(Tox_Pass_Key));
+
+    if (!out_key) {
+        SET_ERROR_PARAMETER(error, TOX_ERR_KEY_DERIVATION_FAILED);
+        return NULL;
+    }
+
     memcpy(out_key->salt, salt, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
     memcpy(out_key->key, key, CRYPTO_SHARED_KEY_SIZE);
     SET_ERROR_PARAMETER(error, TOX_ERR_KEY_DERIVATION_OK);
-    return 1;
+    return out_key;
 }
 
 /* Encrypt arbitrary with a key produced by tox_derive_key_*. The output
@@ -224,10 +227,10 @@ bool tox_pass_key_encrypt(const Tox_Pass_Key *key, const uint8_t *data, size_t d
 bool tox_pass_encrypt(const uint8_t *data, size_t data_len, const uint8_t *passphrase, size_t pplength, uint8_t *out,
                       TOX_ERR_ENCRYPTION *error)
 {
-    Tox_Pass_Key key;
     TOX_ERR_KEY_DERIVATION _error;
+    Tox_Pass_Key *key = tox_pass_key_derive(passphrase, pplength, &_error);
 
-    if (!tox_pass_key_derive(&key, passphrase, pplength, &_error)) {
+    if (!key) {
         if (_error == TOX_ERR_KEY_DERIVATION_NULL) {
             SET_ERROR_PARAMETER(error, TOX_ERR_ENCRYPTION_NULL);
         } else if (_error == TOX_ERR_KEY_DERIVATION_FAILED) {
@@ -237,7 +240,9 @@ bool tox_pass_encrypt(const uint8_t *data, size_t data_len, const uint8_t *passp
         return 0;
     }
 
-    return tox_pass_key_encrypt(&key, data, data_len, out, error);
+    bool result = tox_pass_key_encrypt(key, data, data_len, out, error);
+    tox_pass_key_free(key);
+    return result;
 }
 
 /* This is the inverse of tox_pass_key_encrypt, also using only keys produced by
@@ -315,15 +320,17 @@ bool tox_pass_decrypt(const uint8_t *data, size_t length, const uint8_t *passphr
     memcpy(salt, data + TOX_ENC_SAVE_MAGIC_LENGTH, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
 
     /* derive the key */
-    Tox_Pass_Key key;
+    Tox_Pass_Key *key = tox_pass_key_derive_with_salt(passphrase, pplength, salt, NULL);
 
-    if (!tox_pass_key_derive_with_salt(&key, passphrase, pplength, salt, NULL)) {
+    if (!key) {
         /* out of memory most likely */
         SET_ERROR_PARAMETER(error, TOX_ERR_DECRYPTION_KEY_DERIVATION_FAILED);
         return 0;
     }
 
-    return tox_pass_key_decrypt(&key, data, length, out, error);
+    bool result = tox_pass_key_decrypt(key, data, length, out, error);
+    tox_pass_key_free(key);
+    return result;
 }
 
 /* Determines whether or not the given data is encrypted (by checking the magic number)
diff --git a/toxencryptsave/toxencryptsave.h b/toxencryptsave/toxencryptsave.h
index ef1ab152..c5a1dff9 100644
--- a/toxencryptsave/toxencryptsave.h
+++ b/toxencryptsave/toxencryptsave.h
@@ -99,8 +99,7 @@ typedef enum TOX_ERR_KEY_DERIVATION {
 
     /**
      * The crypto lib was unable to derive a key from the given passphrase,
-     * which is usually a lack of memory issue. The functions accepting keys
-     * do not produce this error.
+     * which is usually a lack of memory issue.
      */
     TOX_ERR_KEY_DERIVATION_FAILED,
 
@@ -241,8 +240,8 @@ bool tox_pass_decrypt(const uint8_t *ciphertext, size_t ciphertext_len, const ui
  * for encryption and decryption. It is derived from a salt and the user-
  * provided password.
  *
- * The Tox_Pass_Key structure is hidden in the implementation. It can be allocated
- * using tox_pass_key_new and must be deallocated using tox_pass_key_free.
+ * The Tox_Pass_Key structure is hidden in the implementation. It can be created
+ * using tox_pass_key_derive or tox_pass_key_derive_with_salt and must be deallocated using tox_pass_key_free.
  */
 #ifndef TOX_PASS_KEY_DEFINED
 #define TOX_PASS_KEY_DEFINED
@@ -250,15 +249,6 @@ typedef struct Tox_Pass_Key Tox_Pass_Key;
 #endif /* TOX_PASS_KEY_DEFINED */
 
 /**
- * Create a new Tox_Pass_Key. The initial value of it is indeterminate. To
- * initialise it, use one of the derive_* functions below.
- *
- * In case of failure, this function returns NULL. The only failure mode at
- * this time is memory allocation failure, so this function has no error code.
- */
-struct Tox_Pass_Key *tox_pass_key_new(void);
-
-/**
  * Deallocate a Tox_Pass_Key. This function behaves like free(), so NULL is an
  * acceptable argument value.
  */
@@ -279,8 +269,8 @@ void tox_pass_key_free(struct Tox_Pass_Key *_key);
  *
  * @return true on success.
  */
-bool tox_pass_key_derive(struct Tox_Pass_Key *_key, const uint8_t *passphrase, size_t passphrase_len,
-                         TOX_ERR_KEY_DERIVATION *error);
+struct Tox_Pass_Key *tox_pass_key_derive(const uint8_t *passphrase, size_t passphrase_len,
+        TOX_ERR_KEY_DERIVATION *error);
 
 /**
  * Same as above, except use the given salt for deterministic key derivation.
@@ -291,8 +281,8 @@ bool tox_pass_key_derive(struct Tox_Pass_Key *_key, const uint8_t *passphrase, s
  *
  * @return true on success.
  */
-bool tox_pass_key_derive_with_salt(struct Tox_Pass_Key *_key, const uint8_t *passphrase, size_t passphrase_len,
-                                   const uint8_t *salt, TOX_ERR_KEY_DERIVATION *error);
+struct Tox_Pass_Key *tox_pass_key_derive_with_salt(const uint8_t *passphrase, size_t passphrase_len,
+        const uint8_t *salt, TOX_ERR_KEY_DERIVATION *error);
 
 /**
  * Encrypt a plain text with a key produced by tox_pass_key_derive or tox_pass_key_derive_with_salt.