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diff --git a/src/lib/crypto/s2k.h b/src/lib/crypto/s2k.h
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+/*
+ * Copyright (c) 2017, [Ribose Inc](https://www.ribose.com).
+ * All rights reserved.
+ *
+ * This code is originally derived from software contributed to
+ * The NetBSD Foundation by Alistair Crooks (agc@netbsd.org), and
+ * carried further by Ribose Inc (https://www.ribose.com).
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef RNP_S2K_H_
+#define RNP_S2K_H_
+
+#include <cstdint>
+#include "repgp/repgp_def.h"
+
+typedef struct pgp_s2k_t pgp_s2k_t;
+
+int pgp_s2k_iterated(pgp_hash_alg_t alg,
+                     uint8_t *      out,
+                     size_t         output_len,
+                     const char *   password,
+                     const uint8_t *salt,
+                     size_t         iterations);
+
+size_t pgp_s2k_decode_iterations(uint8_t encoded_iter);
+
+uint8_t pgp_s2k_encode_iterations(size_t iterations);
+
+// Round iterations to nearest representable value
+size_t pgp_s2k_round_iterations(size_t iterations);
+
+size_t pgp_s2k_compute_iters(pgp_hash_alg_t alg, size_t desired_msec, size_t trial_msec);
+
+/** @brief Derive key from password using the information stored in s2k structure
+ *  @param s2k pointer to s2k structure, filled according to RFC 4880.
+ *  Iterations field may contain encoded ( < 256) or decoded ( > 256) value.
+ *  @param password NULL-terminated password
+ *  @param key buffer to store the derived key, must have at least keysize bytes
+ *  @param keysize number of bytes in the key.
+ *  @return true on success or false otherwise
+ */
+bool pgp_s2k_derive_key(pgp_s2k_t *s2k, const char *password, uint8_t *key, int keysize);
+
+#endif