fix #1124 by adding salt manip functions

Also, all data now has the magic number prepended. This is incompatible
for all but the save/load functions, but I think nothing besides the one
experimental qTox branch used any of those, which is why I feel confident
about the change.

1 files changed, 91 insertions, 45 deletions

diff --git a/toxencryptsave/toxencryptsave.h b/toxencryptsave/toxencryptsave.h
index 14334ea7..5a5ef0cf 100644
--- a/toxencryptsave/toxencryptsave.h
+++ b/toxencryptsave/toxencryptsave.h
@@ -35,46 +35,44 @@ extern "C" {
 typedef struct Tox Tox;
 #endif
 
-// these two functions provide access to these defines in toxencryptsave.c, which
-//otherwise aren't actually available in clients...
+// these functions provide access to these defines in toxencryptsave.c, which
+// otherwise aren't actually available in clients...
 int tox_pass_encryption_extra_length();
 
 int tox_pass_key_length();
 
-/* This "module" provides functions analogous to tox_load and tox_save in toxcore
- * Clients should consider alerting their users that, unlike plain data, if even one bit
- * becomes corrupted, the data will be entirely unrecoverable.
- * Ditto if they forget their password, there is no way to recover the data.
- */
+int tox_pass_salt_length();
 
-/*  return size of the messenger data (for encrypted saving). */
+/*  return size of the messenger data (for encrypted Messenger saving). */
 uint32_t tox_encrypted_size(const Tox *tox);
 
-/* Generates a secret symmetric key from the given passphrase. out_key must be at least
- * tox_pass_key_length() bytes long.
- * Be sure to not compromise the key! Only keep it in memory, do not write to disk.
- * This function is fairly cheap, but irungentoo insists that you be allowed to
- * cache the result if you want, to minimize computation for repeated encryptions.
- * The password is zeroed after key derivation.
- * The key should only be used with the other functions in this module, as it
- * includes a salt.
+/* This "module" provides functions analogous to tox_load and tox_save in toxcore,
+ * as well as functions for encryption of arbitrary client data (e.g. chat logs).
  *
- * returns 0 on success
- * returns -1 on failure
- */
-int tox_derive_key_from_pass(uint8_t *passphrase, uint32_t pplength, uint8_t *out_key);
-
-/* Encrypt arbitrary with a key produced by tox_derive_key_from_pass. The output
- * array must be at least data_len + tox_pass_encryption_extra_length() bytes long.
- * key must be tox_pass_key_length() bytes.
- * If you already have a symmetric key from somewhere besides this module, simply
- * call encrypt_data_symmetric in toxcore/crypto_core directly.
+ * It is conceptually organized into two parts. The first part are the functions
+ * with "key" in the name. To use these functions, first derive an encryption key
+ * from a password with tox_derive_key_from_pass, and use the returned key to
+ * encrypt the data. The second part takes the password itself instead of the key,
+ * and then delegates to the first part to derive the key before de/encryption,
+ * which can simplify client code; however, key derivation is very expensive
+ * compared to the actual encryption, so clients that do a lot of encryption should
+ * favor using the first part intead of the second part.
  *
+ * The encrypted data is prepended with a magic number, to aid validity checking
+ * (no guarantees are made of course).
  *
- * returns 0 on success
- * returns -1 on failure
+ * Clients should consider alerting their users that, unlike plain data, if even one bit
+ * becomes corrupted, the data will be entirely unrecoverable.
+ * Ditto if they forget their password, there is no way to recover the data.
+ */
+
+
+/******************************* BEGIN PART 2 *******************************
+ * For simplicty, the second part of the module is presented first. The API for
+ * the first part is analgous, with some extra functions for key handling. If
+ * your code spends too much time using these functions, consider using the part
+ * 1 functions instead.
  */
-int tox_pass_key_encrypt(const uint8_t *data, uint32_t data_len, const uint8_t *key, uint8_t *out);
 
 /* Encrypts the given data with the given passphrase. The output array must be
  * at least data_len + tox_pass_encryption_extra_length() bytes long. This delegates
@@ -95,39 +93,86 @@ int tox_pass_encrypt(const uint8_t *data, uint32_t data_len, uint8_t *passphrase
  */
 int tox_encrypted_save(const Tox *tox, uint8_t *data, uint8_t *passphrase, uint32_t pplength);
 
-/* Save the messenger data encrypted with the given key from tox_derive_key.
- * data must be at least tox_encrypted_size().
+/* Decrypts the given data with the given passphrase. The output array must be
+ * at least data_len - tox_pass_encryption_extra_length() bytes long. This delegates
+ * to tox_pass_key_decrypt.
+ *
+ * tox_encrypted_load() is a good example of how to use this function.
+ *
+ * returns the length of the output data (== data_len - tox_pass_encryption_extra_length()) on success
+ * returns -1 on failure
+ */
+int tox_pass_decrypt(const uint8_t *data, uint32_t length, uint8_t *passphrase, uint32_t pplength, uint8_t *out);
+
+/* Load the messenger from encrypted data of size length.
  *
  * returns 0 on success
  * returns -1 on failure
  */
-int tox_encrypted_key_save(const Tox *tox, uint8_t *data, uint8_t *key);
+int tox_encrypted_load(Tox *tox, const uint8_t *data, uint32_t length, uint8_t *passphrase, uint32_t pplength);
 
-/* This is the inverse of tox_pass_key_encrypt, also using only keys produced by
- * tox_derive_key_from_pass.
+
+/******************************* BEGIN PART 1 *******************************
+ * And now part "1", which does the actual encryption, and is rather less cpu 
+ * intensive than part one. The first 3 functions are for key handling.
+ */
+
+/* Generates a secret symmetric key from the given passphrase. out_key must be at least
+ * tox_pass_key_length() bytes long.
+ * Be sure to not compromise the key! Only keep it in memory, do not write to disk.
+ * The password is zeroed after key derivation.
+ * The key should only be used with the other functions in this module, as it
+ * includes a salt.
+ * Note that this function is not deterministic; to derive the same key from a
+ * password, you also must know the random salt that was used. See below.
  *
- * returns the length of the output data (== data_len - tox_pass_encryption_extra_length()) on success
+ * returns 0 on success
  * returns -1 on failure
  */
-int tox_pass_key_decrypt(const uint8_t *data, uint32_t length, const uint8_t *key, uint8_t *out);
+int tox_derive_key_from_pass(uint8_t *passphrase, uint32_t pplength, uint8_t *out_key);
 
-/* Decrypts the given data with the given passphrase. The output array must be
- * at least data_len - tox_pass_encryption_extra_length() bytes long. This delegates
- * to tox_pass_key_decrypt.
+/* Same as above, except with use the given salt for deterministic key derivation.
+ * The salt must be tox_salt_length() bytes in length.
+ */
+int tox_derive_key_with_salt(uint8_t *passphrase, uint32_t pplength, uint8_t *salt, uint8_t *out_key);
+
+/* This retrieves the salt used to encrypt the given data, which can then be passed to
+ * derive_key_with_salt to produce the same key as was previously used. Any encrpyted
+ * data with this module can be used as input.
  *
- * tox_encrypted_load() is a good example of how to use this function.
+ * returns -1 if the magic number is wrong
+ * returns 0 otherwise (no guarantee about validity of data)
+ */
+int tox_get_salt(uint8_t *data, uint8_t *salt);
+
+/* Now come the functions that are analogous to the part 2 functions. */
+
+/* Encrypt arbitrary with a key produced by tox_derive_key_. The output
+ * array must be at least data_len + tox_pass_encryption_extra_length() bytes long.
+ * key must be tox_pass_key_length() bytes.
+ * If you already have a symmetric key from somewhere besides this module, simply
+ * call encrypt_data_symmetric in toxcore/crypto_core directly.
  *
- * returns the length of the output data (== data_len - tox_pass_encryption_extra_length()) on success
+ * returns 0 on success
  * returns -1 on failure
  */
-int tox_pass_decrypt(const uint8_t *data, uint32_t length, uint8_t *passphrase, uint32_t pplength, uint8_t *out);
+int tox_pass_key_encrypt(const uint8_t *data, uint32_t data_len, const uint8_t *key, uint8_t *out);
 
-/* Load the messenger from encrypted data of size length.
+/* Save the messenger data encrypted with the given key from tox_derive_key.
+ * data must be at least tox_encrypted_size().
  *
  * returns 0 on success
  * returns -1 on failure
  */
-int tox_encrypted_load(Tox *tox, const uint8_t *data, uint32_t length, uint8_t *passphrase, uint32_t pplength);
+int tox_encrypted_key_save(const Tox *tox, uint8_t *data, uint8_t *key);
+
+/* This is the inverse of tox_pass_key_encrypt, also using only keys produced by
+ * tox_derive_key_from_pass.
+ *
+ * returns the length of the output data (== data_len - tox_pass_encryption_extra_length()) on success
+ * returns -1 on failure
+ */
+int tox_pass_key_decrypt(const uint8_t *data, uint32_t length, const uint8_t *key, uint8_t *out);
 
 /* Load the messenger from encrypted data of size length, with key from tox_derive_key.
  *
@@ -141,7 +186,8 @@ int tox_encrypted_key_load(Tox *tox, const uint8_t *data, uint32_t length, uint8
  * returns 1 if it is encrypted
  * returns 0 otherwise
  */
-int tox_is_save_encrypted(const uint8_t *data);
+int tox_is_data_encrypted(const uint8_t *data);
+int tox_is_save_encrypted(const uint8_t *data); // poorly-named alias for backwards compat (oh irony...)
 
 #ifdef __cplusplus
 }