epee: add SSL support

RPC connections now have optional tranparent SSL.

An optional private key and certificate file can be passed,
using the --{rpc,daemon}-ssl-private-key and
--{rpc,daemon}-ssl-certificate options. Those have as
argument a path to a PEM format private private key and
certificate, respectively.
If not given, a temporary self signed certificate will be used.

SSL can be enabled or disabled using --{rpc}-ssl, which
accepts autodetect (default), disabled or enabled.

Access can be restricted to particular certificates using the
--rpc-ssl-allowed-certificates, which takes a list of
paths to PEM encoded certificates. This can allow a wallet to
connect to only the daemon they think they're connected to,
by forcing SSL and listing the paths to the known good
certificates.

To generate long term certificates:

openssl genrsa -out /tmp/KEY 4096
openssl req -new -key /tmp/KEY -out /tmp/REQ
openssl x509 -req -days 999999 -sha256 -in /tmp/REQ -signkey /tmp/KEY -out /tmp/CERT

/tmp/KEY is the private key, and /tmp/CERT is the certificate,
both in PEM format. /tmp/REQ can be removed. Adjust the last
command to set expiration date, etc, as needed. It doesn't
make a whole lot of sense for monero anyway, since most servers
will run with one time temporary self signed certificates anyway.

SSL support is transparent, so all communication is done on the
existing ports, with SSL autodetection. This means you can start
using an SSL daemon now, but you should not enforce SSL yet or
nothing will talk to you.

2 files changed, 121 insertions, 24 deletions

diff --git a/contrib/epee/src/hex.cpp b/contrib/epee/src/hex.cpp
index 5c8acc8be..8421dcae9 100644
--- a/contrib/epee/src/hex.cpp
+++ b/contrib/epee/src/hex.cpp
@@ -83,4 +83,67 @@ namespace epee
   {
     return write_hex(out, src);
   }
+
+  std::vector<uint8_t> from_hex::vector(boost::string_ref src)
+  {
+    // should we include a specific character
+    auto include = [](char input) {
+        // we ignore spaces and colons
+        return !std::isspace(input) && input != ':';
+    };
+
+    // the number of relevant characters to decode
+    auto count = std::count_if(src.begin(), src.end(), include);
+
+    // this must be a multiple of two, otherwise we have a truncated input
+    if (count % 2) {
+      throw std::length_error{ "Invalid hexadecimal input length" };
+    }
+
+    std::vector<uint8_t> result;
+    result.reserve(count / 2);
+
+    // the data to work with (std::string is always null-terminated)
+    auto data = src.data();
+
+    // convert a single hex character to an unsigned integer
+    auto char_to_int = [](const char *input) {
+      switch (std::tolower(*input)) {
+        case '0': return  0;
+        case '1': return  1;
+        case '2': return  2;
+        case '3': return  3;
+        case '4': return  4;
+        case '5': return  5;
+        case '6': return  6;
+        case '7': return  7;
+        case '8': return  8;
+        case '9': return  9;
+        case 'a': return 10;
+        case 'b': return 11;
+        case 'c': return 12;
+        case 'd': return 13;
+        case 'e': return 14;
+        case 'f': return 15;
+        default:  throw std::range_error{ "Invalid hexadecimal input" };
+      }
+    };
+
+    // keep going until we reach the end
+    while (data[0] != '\0') {
+      // skip unwanted characters
+      if (!include(data[0])) {
+        ++data;
+        continue;
+      }
+
+      // convert two matching characters to int
+      auto high = char_to_int(data++);
+      auto low  = char_to_int(data++);
+
+      result.push_back(high << 4 | low);
+    }
+
+    return result;
+  }
 }
diff --git a/contrib/epee/src/net_ssl.cpp b/contrib/epee/src/net_ssl.cpp
index 941799078..9a62dd3c2 100644
--- a/contrib/epee/src/net_ssl.cpp
+++ b/contrib/epee/src/net_ssl.cpp
@@ -154,13 +154,19 @@ bool create_ssl_certificate(std::string &pkey_buffer, std::string &cert_buffer)
   return success;
 }
 
-ssl_context_t create_ssl_context(const std::pair<std::string, std::string> &private_key_and_certificate_path, std::list<std::string> allowed_certificates, bool allow_any_cert)
+ssl_context_t create_ssl_context(const std::pair<std::string, std::string> &private_key_and_certificate_path, std::list<std::string> allowed_certificates, std::vector<std::vector<uint8_t>> allowed_fingerprints, bool allow_any_cert)
 {
-  ssl_context_t ssl_context({boost::asio::ssl::context(boost::asio::ssl::context::sslv23), std::move(allowed_certificates)});
+  ssl_context_t ssl_context{boost::asio::ssl::context(boost::asio::ssl::context::tlsv12), std::move(allowed_certificates), std::move(allowed_fingerprints)};
 
-  // disable sslv2
-  ssl_context.context.set_options(boost::asio::ssl::context::default_workarounds | boost::asio::ssl::context::no_sslv2);
-  ssl_context.context.set_default_verify_paths();
+  // only allow tls v1.2 and up
+  ssl_context.context.set_options(boost::asio::ssl::context::default_workarounds);
+  ssl_context.context.set_options(boost::asio::ssl::context::no_sslv2);
+  ssl_context.context.set_options(boost::asio::ssl::context::no_sslv3);
+  ssl_context.context.set_options(boost::asio::ssl::context::no_tlsv1);
+  ssl_context.context.set_options(boost::asio::ssl::context::no_tlsv1_1);
+
+  // only allow a select handful of tls v1.3 and v1.2 ciphers to be used
+  SSL_CTX_set_cipher_list(ssl_context.context.native_handle(), "ECDHE-ECDSA-CHACHA20-POLY1305-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-CHACHA20-POLY1305");
 
   // set options on the SSL context for added security
   SSL_CTX *ctx = ssl_context.context.native_handle();
@@ -179,7 +185,7 @@ ssl_context_t create_ssl_context(const std::pair<std::string, std::string> &priv
 #ifdef SSL_OP_NO_COMPRESSION
   SSL_CTX_set_options(ctx, SSL_OP_NO_COMPRESSION);
 #endif
-  SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1); // https://github.com/ssllabs/research/wiki/SSL-and-TLS-Deployment-Best-Practices
+  ssl_context.context.set_default_verify_paths();
 
   CHECK_AND_ASSERT_THROW_MES(private_key_and_certificate_path.first.empty() == private_key_and_certificate_path.second.empty(), "private key and certificate must be either both given or both empty");
   if (private_key_and_certificate_path.second.empty())
@@ -225,7 +231,7 @@ bool is_ssl(const unsigned char *data, size_t len)
   return false;
 }
 
-bool is_certificate_allowed(boost::asio::ssl::verify_context &ctx, const std::list<std::string> &allowed_certificates)
+bool is_certificate_allowed(boost::asio::ssl::verify_context &ctx, const ssl_context_t &ssl_context)
 {
   X509_STORE_CTX *sctx = ctx.native_handle();
   if (!sctx)
@@ -240,23 +246,51 @@ bool is_certificate_allowed(boost::asio::ssl::verify_context &ctx, const std::li
     return false;
   }
 
-  BIO *bio_cert = BIO_new(BIO_s_mem());
-  openssl_bio bio_cert_deleter{bio_cert};
-  bool success = PEM_write_bio_X509(bio_cert, cert);
-  if (!success)
-  {
-    MERROR("Failed to print certificate");
-    return false;
+  // can we check the certificate against a list of fingerprints?
+  if (!ssl_context.allowed_fingerprints.empty()) {
+    // buffer for the certificate digest and the size of the result
+    std::vector<uint8_t> digest(EVP_MAX_MD_SIZE);
+    unsigned int size{ 0 };
+
+    // create the digest from the certificate
+    if (!X509_digest(cert, EVP_sha1(), digest.data(), &size)) {
+      MERROR("Failed to create certificate fingerprint");
+      return false;
+    }
+
+    // strip unnecessary bytes from the digest
+    digest.resize(size);
+
+    // is the certificate fingerprint inside the list of allowed fingerprints?
+    if (std::find(ssl_context.allowed_fingerprints.begin(), ssl_context.allowed_fingerprints.end(), digest) != ssl_context.allowed_fingerprints.end())
+      return true;
   }
-  BUF_MEM *buf = NULL;
-  BIO_get_mem_ptr(bio_cert, &buf);
-  if (!buf || !buf->data || !buf->length)
-  {
-    MERROR("Failed to write certificate: " << ERR_get_error());
-    return false;
+
+  if (!ssl_context.allowed_certificates.empty()) {
+    BIO *bio_cert = BIO_new(BIO_s_mem());
+    bool success = PEM_write_bio_X509(bio_cert, cert);
+    if (!success)
+    {
+      BIO_free(bio_cert);
+      MERROR("Failed to print certificate");
+      return false;
+    }
+    BUF_MEM *buf = NULL;
+    BIO_get_mem_ptr(bio_cert, &buf);
+    if (!buf || !buf->data || !buf->length)
+    {
+      BIO_free(bio_cert);
+      MERROR("Failed to write certificate: " << ERR_get_error());
+      return false;
+    }
+    std::string certificate(std::string(buf->data, buf->length));
+    BIO_free(bio_cert);
+    if (std::find(ssl_context.allowed_certificates.begin(), ssl_context.allowed_certificates.end(), certificate) != ssl_context.allowed_certificates.end())
+      return true;
   }
-  std::string certificate(std::string(buf->data, buf->length));
-  return std::find(allowed_certificates.begin(), allowed_certificates.end(), certificate) != allowed_certificates.end();
+
+  // if either checklist is non-empty we must have failed it
+  return ssl_context.allowed_fingerprints.empty() && ssl_context.allowed_certificates.empty();
 }
 
 bool ssl_handshake(boost::asio::ssl::stream<boost::asio::ip::tcp::socket> &socket, boost::asio::ssl::stream_base::handshake_type type, const epee::net_utils::ssl_context_t &ssl_context)
@@ -276,7 +310,7 @@ bool ssl_handshake(boost::asio::ssl::stream<boost::asio::ip::tcp::socket> &socke
         return false;
       }
     }
-    if (!ssl_context.allow_any_cert && !ssl_context.allowed_certificates.empty() && !is_certificate_allowed(ctx, ssl_context.allowed_certificates))
+    if (!ssl_context.allow_any_cert && !is_certificate_allowed(ctx, ssl_context))
     {
       MERROR("Certificate is not in the allowed list, connection droppped");
       return false;
@@ -289,7 +323,7 @@ bool ssl_handshake(boost::asio::ssl::stream<boost::asio::ip::tcp::socket> &socke
   socket.handshake(type, ec);
   if (ec)
   {
-    MERROR("handshake failed, connection dropped");
+    MERROR("handshake failed, connection dropped: " << ec.message());
     return false;
   }
   if (!ssl_context.allow_any_cert && !verified)