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+Neverbleed
+===============
+
+Neverbleed is an [OpenSSL engine](https://www.openssl.org/docs/manmaster/crypto/engine.html) that runs RSA private key operations in an isolated process, thereby minimizing the risk of private key leak in case of vulnerability such as [Heartbleed](http://heartbleed.com/).
+
+The engine is known to work together with existing versions of OpenSSL or LibreSSL, with minimal changes to the server source code.
+
+FAQ
+---
+
+### Q. How much is the overhead?
+
+Virtually none.
+
+Generally speaking, private key operations are much more heavier than the overhead of inter-process communication.
+On my Linux VM running on Core i7 @ 2.4GHz (MacBook Pro 15" Late 2013), OpenSSL 1.0.2 without privilege separation processes 319.56 full TLS handshakes per second, whereas OpenSSL with privilege separation processes 316.72 handshakes per second (note: RSA key length: 2,048 bits, selected cipher-suite: ECDHE-RSA-AES128-GCM-SHA256).
+
+### Q. Why does the library only protect the private keys?
+
+Because private keys are the only _long-term_ secret being used for encrypting and/or digitally-signing the communication.
+
+Depending on how OpenSSL is used, it might be beneficial to separate symmetric cipher operations or TLS operations as a whole.
+But even in such case, it would still be a good idea to isolate private key operations from them considering the impact of private key leaks.
+In other words, separating private key operations only to an isolated process in always a good thing to do.
+
+### Q. Is there any HTTP server that uses Neverbleed?
+
+Neverbleed is used by [H2O](https://h2o.examp1e.net/) HTTP2 server since version [1.5.0-beta4](https://github.com/h2o/h2o/releases/tag/v1.5.0-beta4).
+
+How-to
+------
+
+The library exposes two functions: `neverbleed_init` and `neverbleed_load_private_key_file`.
+
+The first function spawns an external process dedicated to private key operations, and the second function assigns a RSA private key stored in the specified file to an existing SSL context (`SSL_CTX`).
+
+By
+
+1. adding call to `neverbleed_init`
+2. replacing call to `SSL_CTX_use_PrivateKey_file` with `neverbleed_load_private_key_file`
+
+the privilege separation engine will be used for all the incoming TLS connections.
+
+```
+  neverbleed_t nb;
+  char errbuf[NEVERBLEED_ERRBUF_SIZE];
+
+  /* initialize the OpenSSL library and the neverbleed engine */
+  SSL_load_error_strings();
+  SSL_library_init();
+  OpenSSL_add_all_algorithms();
+  if (neverbleed_init(&nb, errbuf) != 0) {
+    fprintf(stderr, "neverbleed_init failed: %s\n", errbuf);
+    ...
+  }
+
+  ...
+
+  /* load certificate chain and private key */
+  if (SSL_CTX_use_certificate_chain_file(ssl_ctx, certchain_fn) != 1) {
+    fprintf(stderr, "failed to load certificate chain file:%s\n", certchain_fn);
+    ...
+  }
+  if (neverbleed_load_private_key_file(&nb, ctx, privkey_fn, errbuf) != 1) {
+    fprintf(stderr, "failed to load private key from file:%s:%s\n", privkey_fn, errbuf);
+    ...
+  }
+```
+
+Also, `neverbleed_setuidgid` function can be used to drop the privileges of the daemon process once it completes loading all the private keys.