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, 24 insertions, 6 deletions

diff --git a/src/error.c b/src/error.c
index f541a93..5147b5c 100644
--- a/src/error.c
+++ b/src/error.c
@@ -31,6 +31,7 @@ static const char * ERRORS[] = {
     "UNKNOWN_MESSAGE_INDEX",
     "BAD_LEGACY_ACCOUNT_PICKLE",
     "BAD_SIGNATURE",
+    "OLM_INPUT_BUFFER_TOO_SMALL",
 };
 
 const char * _olm_error_to_string(enum OlmErrorCode error)
diff --git a/src/pk.cpp b/src/pk.cpp
index e646dc4..20ab991 100644
--- a/src/pk.cpp
+++ b/src/pk.cpp
@@ -176,7 +176,7 @@ size_t olm_clear_pk_decryption(
     return sizeof(OlmPkDecryption);
 }
 
-size_t olm_pk_generate_key_random_length(void) {
+size_t olm_pk_private_key_length(void) {
     return CURVE25519_KEY_LENGTH;
 }
 
@@ -184,23 +184,23 @@ size_t olm_pk_key_length(void) {
     return olm::encode_base64_length(CURVE25519_KEY_LENGTH);
 }
 
-size_t olm_pk_generate_key(
+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
 ) {
     if (pubkey_length < olm_pk_key_length()) {
         decryption->last_error =
             OlmErrorCode::OLM_OUTPUT_BUFFER_TOO_SMALL;
         return std::size_t(-1);
     }
-    if (random_length < olm_pk_generate_key_random_length()) {
+    if (privkey_length < olm_pk_private_key_length()) {
         decryption->last_error =
-            OlmErrorCode::OLM_NOT_ENOUGH_RANDOM;
+            OlmErrorCode::OLM_INPUT_BUFFER_TOO_SMALL;
         return std::size_t(-1);
     }
 
-    _olm_crypto_curve25519_generate_key((uint8_t *) random, &decryption->key_pair);
+    _olm_crypto_curve25519_generate_key((uint8_t *) privkey, &decryption->key_pair);
     olm::encode_base64((const uint8_t *)decryption->key_pair.public_key.public_key, CURVE25519_KEY_LENGTH, (uint8_t *)pubkey);
     return 0;
 }
@@ -352,4 +352,21 @@ size_t olm_pk_decrypt(
     }
 }
 
+size_t olm_pk_get_private_key(
+    OlmPkDecryption * decryption,
+    void *private_key, size_t private_key_length
+) {
+    if (private_key_length < olm_pk_private_key_length()) {
+        decryption->last_error =
+            OlmErrorCode::OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return std::size_t(-1);
+    }
+    std::memcpy(
+        private_key,
+        decryption->key_pair.private_key.private_key,
+        olm_pk_private_key_length()
+    );
+    return olm_pk_private_key_length();
+}
+
 }