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diff --git a/include/olm/sas.h b/include/olm/sas.h
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+/* Copyright 2018-2019 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.
+ */
+
+
+#ifndef OLM_SAS_H_
+#define OLM_SAS_H_
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** @defgroup SAS Short Authentication String verification
+ * These functions are used for verifying keys using the Short Authentication
+ * String (SAS) method.
+ * @{
+ */
+
+typedef struct OlmSAS OlmSAS;
+
+/** A null terminated string describing the most recent error to happen to an
+ * SAS object. */
+const char * olm_sas_last_error(
+    OlmSAS * sas
+);
+
+/** The size of an SAS object in bytes. */
+size_t olm_sas_size(void);
+
+/** Initialize an SAS object using the supplied memory.
+ * The supplied memory must be at least `olm_sas_size()` bytes. */
+OlmSAS * olm_sas(
+    void * memory
+);
+
+/** Clears the memory used to back an SAS object. */
+size_t olm_clear_sas(
+    OlmSAS * sas
+);
+
+/** The number of random bytes needed to create an SAS object. */
+size_t olm_create_sas_random_length(
+    OlmSAS * sas
+);
+
+/** Creates a new SAS object.
+ *
+ * @param[in] sas the SAS object to create, initialized by `olm_sas()`.
+ * @param[in] random array of random bytes.
+ * @param[in] random_length the number of random bytes provided.  Must be at
+ *    least `olm_create_sas_random_length()`.
+ *
+ * @return `olm_error()` on failure.  If there weren't enough random bytes then
+ * `olm_sas_last_error()` will be `NOT_ENOUGH_RANDOM`.
+ */
+size_t olm_create_sas(
+    OlmSAS * sas,
+    void * random, size_t random_length
+);
+
+/** The size of a public key in bytes. */
+size_t olm_sas_pubkey_length(OlmSAS * sas);
+
+/** Get the public key for the SAS object.
+ *
+ * @param[in] sas the SAS object.
+ * @param[out] pubkey buffer to store the public key.
+ * @param[in] pubkey_length the size of the `pubkey` buffer.  Must be at least
+ *   `olm_sas_pubkey_length()`.
+ *
+ * @return `olm_error()` on failure.  If the `pubkey` buffer is too small, then
+ * `olm_sas_last_error()` will be `OUTPUT_BUFFER_TOO_SMALL`.
+ */
+size_t olm_sas_get_pubkey(
+    OlmSAS * sas,
+    void * pubkey, size_t pubkey_length
+);
+
+/** Sets the public key of other user.
+ *
+ * @param[in] sas the SAS object.
+ * @param[in] their_key the other user's public key.
+ * @param[in] their_key_size the size of the `their_key` buffer.
+ *
+ * @return `olm_error()` on failure.  If the `their_key` buffer is too small,
+ * then `olm_sas_last_error()` will be `INPUT_BUFFER_TOO_SMALL`.
+ */
+size_t olm_sas_set_their_key(
+    OlmSAS *sas,
+    void * their_key, size_t their_key_length
+);
+
+/** Generate bytes to use for the short authentication string.
+ *
+ * @param[in] sas the SAS object.
+ * @param[in] info extra information to mix in when generating the bytes, as
+ *     per the Matrix spec.
+ * @param[in] info_length the length of the `info` parameter.
+ * @param[out] output the output buffer.
+ * @param[in] output_length the size of the output buffer.  For hex-based SAS
+ *     as in the Matrix spec, this will be 5.
+ */
+size_t olm_sas_generate_bytes(
+    OlmSAS * sas,
+    const void * info, size_t info_length,
+    void * output, size_t output_length
+);
+
+/** The size of the message authentication code generated by
+ * olm_sas_calculate_mac()`. */
+size_t olm_sas_mac_length(
+    OlmSAS *sas
+);
+
+/** Generate a message authentication code (MAC) based on the shared secret.
+ *
+ * @param[in] sas the SAS object.
+ * @param[in] input the message to produce the authentication code for.
+ * @param[in] input_length the length of the message.
+ * @param[in] info extra information to mix in when generating the MAC, as per
+ *     the Matrix spec.
+ * @param[in] info_length the length of the `info` parameter.
+ * @param[out] mac the buffer in which to store the MAC.
+ * @param[in] mac_length the size of the `mac` buffer.  Must be at least
+ * `olm_sas_mac_length()`
+ *
+ * @return `olm_error()` on failure.  If the `mac` buffer is too small, then
+ * `olm_sas_last_error()` will be `OUTPUT_BUFFER_TOO_SMALL`.
+ */
+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
+);
+
+/** @} */ // end of SAS group
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif /* OLM_SAS_H_ */