Work with PkDecryption keys by their private keys

Change interface to allow the app to get the private part of the
key and instantiate a decryption object from just the private part
of the key.

Changes the function generating a key from random bytes to be
initialising a key with a private key (because it's exactly the
same thing). Exports & imports private key parts as ArrayBuffer at
JS level rather than base64 assuming we are moving that way in
general.

2 files changed, 37 insertions, 11 deletions

diff --git a/include/olm/error.h b/include/olm/error.h
index 9d44a94..ee2187c 100644
--- a/include/olm/error.h
+++ b/include/olm/error.h
@@ -51,6 +51,13 @@ enum OlmErrorCode {
      */
     OLM_BAD_SIGNATURE = 14,
 
+    OLM_INPUT_BUFFER_TOO_SMALL = 15,
+
+    // Not an error code, just here to pad out the enum past 16 because
+    // otherwise the compiler warns about a redunant check. If you're
+    // adding an error code, replace this one!
+    OLM_ERROR_NOT_INVENTED_YET = 16,
+
     /* remember to update the list of string constants in error.c when updating
      * this list. */
 };
diff --git a/include/olm/pk.h b/include/olm/pk.h
index 1f3f9ff..5e779ce 100644
--- a/include/olm/pk.h
+++ b/include/olm/pk.h
@@ -76,7 +76,7 @@ size_t olm_pk_encrypt_random_length(
  * ciphertext, mac, or ephemeral_key buffers were too small then
  * olm_pk_encryption_last_error() will be "OUTPUT_BUFFER_TOO_SMALL". If there
  * weren't enough random bytes then olm_pk_encryption_last_error() will be
- * "NOT_ENOUGH_RANDOM". */
+ * "OLM_INPUT_BUFFER_TOO_SMALL". */
 size_t olm_pk_encrypt(
     OlmPkEncryption *encryption,
     void const * plaintext, size_t plaintext_length,
@@ -108,18 +108,24 @@ size_t olm_clear_pk_decryption(
     OlmPkDecryption *decryption
 );
 
-/** The number of random bytes needed to generate a new key. */
-size_t olm_pk_generate_key_random_length(void);
-
-/** Generate a new key to use for decrypting messages. The associated public
- * key will be written to the pubkey buffer. Returns olm_error() on failure. If
- * the pubkey buffer is too small then olm_pk_decryption_last_error() will be
- * "OUTPUT_BUFFER_TOO_SMALL". If there weren't enough random bytes then
- * olm_pk_decryption_last_error() will be "NOT_ENOUGH_RANDOM". */
-size_t olm_pk_generate_key(
+/** Get the number of bytes required to store an olm private key
+ */
+size_t olm_pk_private_key_length();
+
+/** Initialise the key from the private part of a key as returned by
+ * olm_pk_get_private_key(). The associated public key will be written to the
+ * pubkey buffer. Returns olm_error() on failure. If the pubkey buffer is too
+ * small then olm_pk_decryption_last_error() will be "OUTPUT_BUFFER_TOO_SMALL".
+ * If the private key was not long enough then olm_pk_decryption_last_error()
+ * will be "OLM_INPUT_BUFFER_TOO_SMALL".
+ *
+ * Note that the pubkey is a base64 encoded string, but the private key is
+ * an unencoded byte array
+ */
+size_t olm_pk_key_from_private(
     OlmPkDecryption * decryption,
     void * pubkey, size_t pubkey_length,
-    void * random, size_t random_length
+    void * privkey, size_t privkey_length
 );
 
 /** Returns the number of bytes needed to store a decryption object. */
@@ -171,6 +177,19 @@ size_t olm_pk_decrypt(
     void * plaintext, size_t max_plaintext_length
 );
 
+/**
+ * Get the private key for an OlmDecryption object as an unencoded byte array
+ * private_key must be a pointer to a buffer of at least
+ * olm_pk_private_key_length() bytes and this length must be passed in
+ * private_key_length. If the given buffer is too small, returns olm_error()
+ * and olm_pk_encryption_last_error() will be "OUTPUT_BUFFER_TOO_SMALL".
+ * Returns the number of bytes written.
+ */
+size_t olm_pk_get_private_key(
+    OlmPkDecryption * decryption,
+    void *private_key, size_t private_key_length
+);
+
 #ifdef __cplusplus
 }
 #endif