initial implementation of short authentication string generation

1 files changed, 140 insertions, 0 deletions

diff --git a/src/sas.c b/src/sas.c
new file mode 100644
index 0000000..6de6278
--- /dev/null
+++ b/src/sas.c
@@ -0,0 +1,140 @@
+/* Copyright 2018 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "olm/sas.h"
+#include "olm/base64.h"
+#include "olm/crypto.h"
+#include "olm/error.h"
+#include "olm/memory.h"
+
+struct OlmSAS {
+    enum OlmErrorCode last_error;
+    struct _olm_curve25519_key_pair curve25519_key;
+    uint8_t secret[CURVE25519_SHARED_SECRET_LENGTH];
+};
+
+const char * olm_sas_last_error(
+    OlmSAS * sas
+) {
+    return _olm_error_to_string(sas->last_error);
+}
+
+size_t olm_sas_size(void) {
+    return sizeof(OlmSAS);
+}
+
+OlmSAS * olm_sas(
+    void * memory
+) {
+    _olm_unset(memory, sizeof(OlmSAS));
+    return (OlmSAS *) memory;
+}
+
+size_t olm_clear_sas(
+    OlmSAS * sas
+) {
+    _olm_unset(sas, sizeof(OlmSAS));
+    return sizeof(OlmSAS);
+}
+
+size_t olm_create_sas_random_length(OlmSAS * sas) {
+    return CURVE25519_KEY_LENGTH;
+}
+
+size_t olm_create_sas(
+    OlmSAS * sas,
+    void * random, size_t random_length
+) {
+    if (random_length < olm_create_sas_random_length(sas)) {
+        sas->last_error = OLM_NOT_ENOUGH_RANDOM;
+        return (size_t)-1;
+    }
+    _olm_crypto_curve25519_generate_key((uint8_t *) random, &sas->curve25519_key);
+    return 0;
+}
+
+size_t olm_sas_pubkey_length(OlmSAS * sas) {
+    return _olm_encode_base64_length(CURVE25519_KEY_LENGTH);
+}
+
+size_t olm_sas_get_pubkey(
+    OlmSAS * sas,
+    void * pubkey, size_t pubkey_length
+) {
+    if (pubkey_length < olm_sas_pubkey_length(sas)) {
+        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+    _olm_encode_base64(
+        (const uint8_t *)sas->curve25519_key.public_key.public_key,
+        CURVE25519_KEY_LENGTH,
+        (uint8_t *)pubkey
+    );
+    return 0;
+}
+
+size_t olm_sas_set_their_key(
+    OlmSAS *sas,
+    void * their_key, size_t their_key_length
+) {
+    if (their_key_length < olm_sas_pubkey_length(sas)) {
+        sas->last_error = OLM_INPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+    _olm_decode_base64(their_key, their_key_length, their_key);
+    _olm_crypto_curve25519_shared_secret(&sas->curve25519_key, their_key, sas->secret);
+    return 0;
+}
+
+size_t olm_sas_generate_bytes(
+    OlmSAS * sas,
+    void * output, size_t output_length
+) {
+    _olm_crypto_hkdf_sha256(
+        sas->secret, sizeof(sas->secret),
+        NULL, 0,
+        (const uint8_t *) "SAS", 3,
+        output, output_length
+    );
+    return 0;
+}
+
+size_t olm_sas_mac_length(
+    OlmSAS *sas
+) {
+    return _olm_encode_base64_length(SHA256_OUTPUT_LENGTH);
+}
+
+size_t olm_sas_calculate_mac(
+    OlmSAS * sas,
+    void * input, size_t input_length,
+    void * mac, size_t mac_length
+) {
+    if (mac_length < olm_sas_mac_length(sas)) {
+        sas->last_error = OLM_OUTPUT_BUFFER_TOO_SMALL;
+        return (size_t)-1;
+    }
+    // FIXME: base64-decode input?
+    uint8_t key[256];
+    _olm_crypto_hkdf_sha256(
+        sas->secret, sizeof(sas->secret),
+        NULL, 0,
+        (const uint8_t *) "MAC", 3,
+        key, 256
+    );
+    _olm_crypto_hmac_sha256(key, 256, input, input_length, mac);
+    _olm_encode_base64((const uint8_t *)mac, SHA256_OUTPUT_LENGTH, (uint8_t *)mac);
+    return 0;
+}