-void threefish256_enc(void* data, threefish256_ctx_t* ctx);
-void threefish512_enc(void* data, threefish512_ctx_t* ctx);
-void threefish1024_enc(void* data, threefish1024_ctx_t* ctx);
+void threefish256_enc(void* data, const threefish256_ctx_t* ctx);
+void threefish512_enc(void* data, const threefish512_ctx_t* ctx);
+void threefish1024_enc(void* data, const threefish1024_ctx_t* ctx);
+
+void threefish256_dec(void* data, const threefish256_ctx_t* ctx);