+/**
+ * Allocate and initialize a stream cipher structure.
+ *
+ * \param data The key.
+ * \param len The size of the key.
+ *
+ * \return A new stream cipher structure.
+ */
+struct stream_cipher *sc_new(const unsigned char *data, int len);
+
+/**
+ * Encrypt or decrypt a buffer using a stream cipher.
+ *
+ * \param sc Crypto key.
+ * \param src The source buffer and length.
+ * \param dst The destination buffer and length, filled out by the function.
+ *
+ * It is up to the implementation to decide whether the crypt operation is
+ * performed in place. The caller can tell by looking if the buffers given by
+ * \a src and \a dst coincide after the call. If (and only if) the crypt
+ * operation was not performed in place, the function allocated a new buffer
+ * for the result, so dst->iov_base is different from src->iov_base. In this
+ * case, the destination buffer must be freed by the caller when it is no
+ * longer needed.
+ */
+void sc_crypt(struct stream_cipher *sc, struct iovec *src, struct iovec *dst);
+
+/**
+ * Wrapper for \ref sc_crypt() that can be used as a sideband transformation.
+ *
+ * \param src Passed verbatim to \ref sc_crypt().
+ * \param dst Passed verbatim to \ref sc_crypt().
+ * \param trafo_context Must point to an initialized stream cipher.
+ */
+_static_inline_ void sc_trafo(struct iovec *src, struct iovec *dst,
+ void *trafo_context)
+{
+ sc_crypt(trafo_context, src, dst);
+}
+
+/**
+ * Deallocate a stream cipher structure.
+ *
+ * \param sc A stream cipher previously obtained by sc_new().
+ */
+void sc_free(struct stream_cipher *sc);
+
+/**
+ * Encrypt and send a buffer.
+ *
+ * \param scc The context.
+ * \param buf The buffer to send.
+ * \param len The size of \a buf in bytes.
+ *
+ * \return The return value of the underyling call to write_all().
+ *
+ * \sa \ref write_all(), RC4(3).
+ */
+int sc_send_bin_buffer(struct stream_cipher_context *scc, char *buf,
+ size_t len);
+
+/**
+ * Encrypt and send a \p NULL-terminated buffer.
+ *
+ * \param scc The context.
+ * \param buf The buffer to send.
+ *
+ * \return The return value of the underyling call to sc_send_bin_buffer().
+ */
+int sc_send_buffer(struct stream_cipher_context *scc, char *buf);
+
+/**
+ * Format, encrypt and send a buffer.
+ *
+ * \param scc The context.
+ * \param fmt A format string.
+ *
+ * \return The return value of the underyling call to sc_send_buffer().
+ */
+__printf_2_3 int sc_send_va_buffer(struct stream_cipher_context *scc,
+ const char *fmt, ...);
+
+/**
+ * Receive a buffer and decrypt it.
+ *
+ * \param scc The context.
+ * \param buf The buffer to write the decrypted data to.
+ * \param size The size of \a buf.
+ *
+ * \return The number of bytes received on success, negative on errors, zero if
+ * the peer has performed an orderly shutdown.
+ *
+ * \sa recv(2), RC4(3).
+ */
+int sc_recv_bin_buffer(struct stream_cipher_context *scc, char *buf,
+ size_t size);
+
+/**
+ * Receive a buffer, decrypt it and write terminating NULL byte.
+ *
+ * \param scc The context.
+ * \param buf The buffer to write the decrypted data to.
+ * \param size The size of \a buf.
+ *
+ * Read at most \a size - 1 bytes from file descriptor given by \a scc, decrypt
+ * the received data and write a NULL byte at the end of the decrypted data.
+ *
+ * \return The return value of the underlying call to \ref
+ * sc_recv_bin_buffer().
+ */
+int sc_recv_buffer(struct stream_cipher_context *scc, char *buf, size_t size);
+
+/** Size of the hash value in bytes. */
+#define HASH_SIZE 20
+
+
+/**
+ * Compute the hash of the given input data.
+ *
+ * \param data Pointer to the data to compute the hash value from.
+ * \param len The length of \a data in bytes.
+ * \param hash Result pointer.
+ *
+ * \a hash must point to an area at least \p HASH_SIZE bytes large.
+ *
+ * \sa sha(3), openssl(1).
+ * */
+void hash_function(const char *data, unsigned long len, unsigned char *hash);
+
+/**
+ * Convert a hash value to ascii format.
+ *
+ * \param hash the hash value.
+ * \param asc Result pointer.
+ *
+ * \a asc must point to an area of at least 2 * \p HASH_SIZE + 1 bytes which
+ * will be filled by the function with the ascii representation of the hash
+ * value given by \a hash, and a terminating \p NULL byte.
+ */
+void hash_to_asc(unsigned char *hash, char *asc);
+
+/**
+ * Compare two hashes.
+ *
+ * \param h1 Pointer to the first hash value.
+ * \param h2 Pointer to the second hash value.
+ *
+ * \return 1, -1, or zero, depending on whether \a h1 is greater than,
+ * less than or equal to h2, respectively.
+ */
+int hash_compare(unsigned char *h1, unsigned char *h2);