re-refactor to separate pass->key and key->encryption

2 files changed, 108 insertions, 25 deletions

diff --git a/toxencryptsave/toxencryptsave.c b/toxencryptsave/toxencryptsave.c
index b018bd48..953ee802 100644
--- a/toxencryptsave/toxencryptsave.c
+++ b/toxencryptsave/toxencryptsave.c
@@ -47,13 +47,19 @@ uint32_t tox_encrypted_size(const Tox *tox)
     return tox_size(tox) + TOX_PASS_ENCRYPTION_EXTRA_LENGTH + TOX_ENC_SAVE_MAGIC_LENGTH;
 }
 
-/* Encrypts the given data with the given passphrase. The output array must be
- * at least data_len + TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long.
+/* 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.
  *
  * returns 0 on success
  * returns -1 on failure
  */
-int tox_pass_encrypt(uint8_t* data, uint32_t data_len, uint8_t* passphrase, uint32_t pplength, uint8_t* out)
+int tox_derive_key_from_pass(uint8_t* passphrase, uint32_t pplength, uint8_t* out_key)
 {
     if (pplength == 0)
         return -1;
@@ -77,7 +83,23 @@ int tox_pass_encrypt(uint8_t* data, uint32_t data_len, uint8_t* passphrase, uint
     }
 
     sodium_memzero(passkey, crypto_hash_sha256_BYTES); /* wipe plaintext pw */
+    memcpy(out_key, salt, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
+    memcpy(out_key + crypto_pwhash_scryptsalsa208sha256_SALTBYTES, key, crypto_box_KEYBYTES);
+    return 0;
+}
 
+/* 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.
+ *
+ *
+ * returns 0 on success
+ * returns -1 on failure
+ */
+int tox_pass_key_encrypt(uint8_t* data, uint32_t data_len, const uint8_t* key, uint8_t* out)
+{
     /* the output data consists of, in order:
      * salt, nonce, mac, enc_data
      * where the mac is automatically prepended by the encrypt()
@@ -88,9 +110,10 @@ int tox_pass_encrypt(uint8_t* data, uint32_t data_len, uint8_t* passphrase, uint
 
     /* first add the prefix */
     uint8_t nonce[crypto_box_NONCEBYTES];
-    random_nonce(nonce);
+    random_nonce(nonce);    
 
-    memcpy(out, salt, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
+    memcpy(out, key, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
+    key += crypto_pwhash_scryptsalsa208sha256_SALTBYTES;
     out += crypto_pwhash_scryptsalsa208sha256_SALTBYTES;
     memcpy(out, nonce, crypto_box_NONCEBYTES);
     out += crypto_box_NONCEBYTES;
@@ -104,6 +127,22 @@ int tox_pass_encrypt(uint8_t* data, uint32_t data_len, uint8_t* passphrase, uint
     return 0;
 }
 
+/* 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
+ * to tox_derive_key_from_pass and tox_pass_key_encrypt.
+ *
+ * returns 0 on success
+ * returns -1 on failure
+ */
+int tox_pass_encrypt(uint8_t* data, uint32_t data_len, uint8_t* passphrase, uint32_t pplength, uint8_t* out)
+{
+    uint8_t key[TOX_PASS_KEY_LENGTH];
+    if (tox_derive_key_from_pass(passphrase, pplength, key) == -1)
+        return -1;
+
+    return tox_pass_key_encrypt(data, data_len, key, out);
+}
+
 /* Save the messenger data encrypted with the given password.
  * data must be at least tox_encrypted_size().
  *
@@ -122,40 +161,61 @@ int tox_encrypted_save(const Tox *tox, uint8_t *data, uint8_t *passphrase, uint3
     memcpy(data, TOX_ENC_SAVE_MAGIC_NUMBER, TOX_ENC_SAVE_MAGIC_LENGTH);
     data += TOX_ENC_SAVE_MAGIC_LENGTH;
 
-
     /* now encrypt */
     return tox_pass_encrypt(temp_data, temp_size, passphrase, pplength, data);
 }
 
-
-/* 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 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_decrypt(const uint8_t* data, uint32_t length, uint8_t* passphrase, uint32_t pplength, uint8_t* out)
+int tox_pass_key_decrypt(const uint8_t* data, uint32_t length, const uint8_t* key, uint8_t* out)
 {
     if (length <= TOX_PASS_ENCRYPTION_EXTRA_LENGTH)
         return -1;
 
     uint32_t decrypt_length = length - TOX_PASS_ENCRYPTION_EXTRA_LENGTH;
-    uint8_t salt[crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
+    //uint8_t salt[crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
     uint8_t nonce[crypto_box_NONCEBYTES];
 
-    uint8_t passkey[crypto_hash_sha256_BYTES];
-    crypto_hash_sha256(passkey, passphrase, pplength);
-
-    memcpy(salt, data, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
+    //memcpy(salt, data, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);
+    key += crypto_pwhash_scryptsalsa208sha256_SALTBYTES; // ignore the salt, which is only needed for kdf
     data += crypto_pwhash_scryptsalsa208sha256_SALTBYTES;
     memcpy(nonce, data, crypto_box_NONCEBYTES);
     data += crypto_box_NONCEBYTES;
 
+    /* decrypt the data */
+    if (decrypt_data_symmetric(key, nonce, data, decrypt_length + crypto_box_MACBYTES, out)
+            != decrypt_length) {
+        return -1;
+    }
+
+    return decrypt_length;
+}
+
+/* Decrypts the given data with the given passphrase. The output array must be
+ * at least data_len - TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long.
+ *
+ * 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)
+{
+    
+    uint8_t passkey[crypto_hash_sha256_BYTES];
+    crypto_hash_sha256(passkey, passphrase, pplength);
+
+    uint8_t salt[crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
+    memcpy(salt, data, crypto_pwhash_scryptsalsa208sha256_SALTBYTES);    
+
     /* derive the key */
-    uint8_t key[crypto_box_KEYBYTES];
+    uint8_t key[crypto_box_KEYBYTES + crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
 
     if (crypto_pwhash_scryptsalsa208sha256(
-                key, sizeof(key), passkey, sizeof(passkey), salt,
+                key + crypto_pwhash_scryptsalsa208sha256_SALTBYTES,
+                crypto_box_KEYBYTES, passkey, sizeof(passkey), salt,
                 crypto_pwhash_scryptsalsa208sha256_OPSLIMIT_INTERACTIVE * 2, /* slightly stronger */
                 crypto_pwhash_scryptsalsa208sha256_MEMLIMIT_INTERACTIVE) != 0) {
         /* out of memory most likely */
@@ -164,13 +224,7 @@ int tox_pass_decrypt(const uint8_t* data, uint32_t length, uint8_t* passphrase,
 
     sodium_memzero(passkey, crypto_hash_sha256_BYTES); /* wipe plaintext pw */
 
-    /* decrypt the data */
-    if (decrypt_data_symmetric(key, nonce, data, decrypt_length + crypto_box_MACBYTES, out)
-            != decrypt_length) {
-        return -1;
-    }
-
-    return decrypt_length;
+    return tox_pass_key_decrypt(data, length, key, out);
 }
 
 /* Load the messenger from encrypted data of size length.
diff --git a/toxencryptsave/toxencryptsave.h b/toxencryptsave/toxencryptsave.h
index e3f998af..b85d945c 100644
--- a/toxencryptsave/toxencryptsave.h
+++ b/toxencryptsave/toxencryptsave.h
@@ -38,6 +38,8 @@ typedef struct Tox Tox;
 #define TOX_PASS_ENCRYPTION_EXTRA_LENGTH (crypto_box_MACBYTES + crypto_box_NONCEBYTES \
            + crypto_pwhash_scryptsalsa208sha256_SALTBYTES)
 
+#define TOX_PASS_KEY_LENGTH (crypto_box_KEYBYTES + crypto_pwhash_scryptsalsa208sha256_SALTBYTES)
+
 /* 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.
@@ -47,8 +49,35 @@ typedef struct Tox Tox;
 /*  return size of the messenger data (for encrypted 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.
+ *
+ * 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.
+ *
+ *
+ * returns 0 on success
+ * returns -1 on failure
+ */
+int tox_pass_key_encrypt(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.
+ * at least data_len + TOX_PASS_ENCRYPTION_EXTRA_LENGTH bytes long. This delegates
+ * to tox_derive_key_from_pass and tox_pass_key_encrypt.
  *
  * tox_encrypted_save() is a good example of how to use this function.
  *