allow specifying the info parameter for the HKDF

include/olm/sas.h

@@ -62,6 +62,7 @@ size_t olm_sas_set_their_key(
 
 size_t olm_sas_generate_bytes(
     OlmSAS * sas,
+    const void * info, size_t info_length,
     void * output, size_t output_length
 );
 
@@ -72,6 +73,7 @@ size_t olm_sas_mac_length(
 size_t olm_sas_calculate_mac(
     OlmSAS * sas,
     void * input, size_t input_length,
+    const void * info, size_t info_length,
     void * mac, size_t mac_length
 );
 

javascript/olm_sas.js

@@ -42,10 +42,13 @@ SAS.prototype['set_their_key'] = restore_stack(function(their_key) {
     );
 });
 
-SAS.prototype['generate_bytes'] = restore_stack(function(length) {
+SAS.prototype['generate_bytes'] = restore_stack(function(info, length) {
+    var info_array = array_from_string(info);
+    var info_buffer = stack(info_array);
     var output_buffer = stack(length);
     sas_method(Module['_olm_sas_generate_bytes'])(
         this.ptr,
+        info_buffer, info_array.length,
         output_buffer, length
     );
     // The inner Uint8Array creates a view of the buffer.  The outer Uint8Array
@@ -57,14 +60,17 @@ SAS.prototype['generate_bytes'] = restore_stack(function(length) {
     return output_arr;
 });
 
-SAS.prototype['calculate_mac'] = restore_stack(function(input) {
+SAS.prototype['calculate_mac'] = restore_stack(function(input, info) {
     var input_array = array_from_string(input);
-    var input_buffer = stack(input_array)
+    var input_buffer = stack(input_array);
+    var info_array = array_from_string(info);
+    var info_buffer = stack(info_array);
     var mac_length = sas_method(Module['_olm_sas_mac_length'])(this.ptr);
     var mac_buffer = stack(mac_length + NULL_BYTE_PADDING_LENGTH);
     sas_method(Module['_olm_sas_calculate_mac'])(
         this.ptr,
         input_buffer, input_array.length,
+        info_buffer, info_array.length,
         mac_buffer, mac_length
     );
     return Pointer_stringify(mac_buffer);

javascript/test/sas.spec.js

@@ -42,12 +42,12 @@ describe("sas", function() {
     it('should create matching SAS bytes', function () {
         alice.set_their_key(bob.get_pubkey());
         bob.set_their_key(alice.get_pubkey());
-        expect(alice.generate_bytes(5).toString()).toEqual(bob.generate_bytes(5).toString());
+        expect(alice.generate_bytes("SAS", 5).toString()).toEqual(bob.generate_bytes("SAS", 5).toString());
     });
 
     it('should create matching MACs', function () {
         alice.set_their_key(bob.get_pubkey());
         bob.set_their_key(alice.get_pubkey());
-        expect(alice.calculate_mac("test").toString()).toEqual(bob.calculate_mac("test").toString());
+        expect(alice.calculate_mac("test", "MAC").toString()).toEqual(bob.calculate_mac("test", "MAC").toString());
     });
 });

src/sas.c

@@ -100,12 +100,13 @@ size_t olm_sas_set_their_key(
 
 size_t olm_sas_generate_bytes(
     OlmSAS * sas,
+    const void * info, size_t info_length,
     void * output, size_t output_length
 ) {
     _olm_crypto_hkdf_sha256(
         sas->secret, sizeof(sas->secret),
         NULL, 0,
-        (const uint8_t *) "SAS", 3,
+        (const uint8_t *) info, info_length,
         output, output_length
     );
     return 0;
@@ -120,6 +121,7 @@ size_t olm_sas_mac_length(
 size_t olm_sas_calculate_mac(
     OlmSAS * sas,
     void * input, size_t input_length,
+    const void * info, size_t info_length,
     void * mac, size_t mac_length
 ) {
     if (mac_length < olm_sas_mac_length(sas)) {
@@ -131,7 +133,7 @@ size_t olm_sas_calculate_mac(
     _olm_crypto_hkdf_sha256(
         sas->secret, sizeof(sas->secret),
         NULL, 0,
-        (const uint8_t *) "MAC", 3,
+        (const uint8_t *) info, info_length,
         key, 256
     );
     _olm_crypto_hmac_sha256(key, 256, input, input_length, mac);

tests/test_sas.cpp

@@ -55,8 +55,8 @@ olm_sas_set_their_key(alice_sas, pubkey, olm_sas_pubkey_length(alice_sas));
 std::uint8_t alice_bytes[6];
 std::uint8_t bob_bytes[6];
 
-olm_sas_generate_bytes(alice_sas, alice_bytes, 6);
-olm_sas_generate_bytes(bob_sas, bob_bytes, 6);
+olm_sas_generate_bytes(alice_sas, "SAS", 3, alice_bytes, 6);
+olm_sas_generate_bytes(bob_sas, "SAS", 3, bob_bytes, 6);
 
 assert_equals(alice_bytes, bob_bytes, 6);
 
@@ -108,8 +108,8 @@ olm_sas_set_their_key(alice_sas, pubkey, olm_sas_pubkey_length(alice_sas));
 std::uint8_t alice_mac[olm_sas_mac_length(alice_sas)];
 std::uint8_t bob_mac[olm_sas_mac_length(bob_sas)];
 
-olm_sas_calculate_mac(alice_sas, (void *) "Hello world!", 12, alice_mac, olm_sas_mac_length(alice_sas));
-olm_sas_calculate_mac(bob_sas, (void *) "Hello world!", 12, bob_mac, olm_sas_mac_length(bob_sas));
+olm_sas_calculate_mac(alice_sas, (void *) "Hello world!", 12, "MAC", 3, alice_mac, olm_sas_mac_length(alice_sas));
+olm_sas_calculate_mac(bob_sas, (void *) "Hello world!", 12, "MAC", 3, bob_mac, olm_sas_mac_length(bob_sas));
 
 assert_equals(alice_mac, bob_mac, olm_sas_mac_length(alice_sas));