Add a basic signing tool.

This is mostly to make it easier for me to generate test Ed25519
certificates.

Change-Id: I45e42f556d949d62eb6cdf684194958fa9f909bf
Reviewed-on: https://boringssl-review.googlesource.com/14504
Reviewed-by: Adam Langley <agl@google.com>

tool/sign.cc

diff --git a/tool/sign.cc b/tool/sign.cc
new file mode 100644
index 0000000..74b84f1
--- /dev/null
+++ b/tool/sign.cc
@@ -0,0 +1,88 @@
+/* Copyright (c) 2017, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include <map>
+#include <vector>
+
+#include <openssl/bio.h>
+#include <openssl/evp.h>
+#include <openssl/pem.h>
+
+#include "internal.h"
+
+
+static const struct argument kArguments[] = {
+    {"-key", kRequiredArgument, "The private key, in PEM format, to sign with"},
+    {"-digest", kOptionalArgument, "The digest algorithm to use"},
+    {"", kOptionalArgument, ""},
+};
+
+bool Sign(const std::vector<std::string> &args) {
+  std::map<std::string, std::string> args_map;
+  if (!ParseKeyValueArguments(&args_map, args, kArguments)) {
+    PrintUsage(kArguments);
+    return false;
+  }
+
+  // Load the private key.
+  bssl::UniquePtr<BIO> bio(BIO_new(BIO_s_file()));
+  if (!bio || !BIO_read_filename(bio.get(), args_map["-key"].c_str())) {
+    return false;
+  }
+  bssl::UniquePtr<EVP_PKEY> key(
+      PEM_read_bio_PrivateKey(bio.get(), nullptr, nullptr, nullptr));
+  if (!key) {
+    return false;
+  }
+
+  // Setup the signing operation.
+  bssl::UniquePtr<EVP_PKEY_CTX> ctx(EVP_PKEY_CTX_new(key.get(), nullptr));
+  if (!ctx ||
+      !EVP_PKEY_sign_init(ctx.get())) {
+    return false;
+  }
+
+  if (args_map.count("-digest")) {
+    const EVP_MD *md = EVP_get_digestbyname(args_map["-digest"].c_str());
+    if (md == nullptr) {
+      fprintf(stderr, "Unknown digest algorithm: %s\n",
+              args_map["-digest"].c_str());
+      return false;
+    }
+
+    if (!EVP_PKEY_CTX_set_signature_md(ctx.get(), md)) {
+      return false;
+    }
+  }
+
+  std::vector<uint8_t> data;
+  if (!ReadAll(&data, stdin)) {
+    fprintf(stderr, "Error reading input.\n");
+    return false;
+  }
+
+  size_t sig_len = EVP_PKEY_size(key.get());
+  std::unique_ptr<uint8_t[]> sig(new uint8_t[sig_len]);
+  if (!EVP_PKEY_sign_message(ctx.get(), sig.get(), &sig_len, data.data(),
+                             data.size())) {
+    return false;
+  }
+
+  if (fwrite(sig.get(), 1, sig_len, stdout) != sig_len) {
+    fprintf(stderr, "Error writing signature.\n");
+    return false;
+  }
+
+  return true;
+}