Add 'generate-ech' command to bssl tool

The tool generates three files: an ECHConfig, its corresponding private
key, and the ECHConfig wrapped in an ECHConfigList.

For example, the following invocation generates the files:

    bssl generate-ech \
      -out-ech-config-list ech_config_list.data \
      -out-ech-config ech_config.data \
      -out-private-key ech.key \
      -public-name foo.example \
      -config-id 0

Now, we can pass the ECHConfig and private key into the 'server' and
'client' commands:

    bssl server -accept 4430 \
        -ech-config ech_config.data \
        -ech-key    ech.key

    bssl client -connect localhost:4430 \
        -ech-config-list ech_config_list.data

Bug: 275
Change-Id: Id4342855483fb01aa956f9aff356105c4a8ca4f6
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48466
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/tool/tool.cc b/tool/tool.cc
index d278535..7bec7a2 100644
--- a/tool/tool.cc
+++ b/tool/tool.cc
@@ -45,6 +45,7 @@ static const Tool kTools[] = {
   { "ciphers", Ciphers },
   { "client", Client },
   { "isfips", IsFIPS },
+  { "generate-ech", GenerateECH},
   { "generate-ed25519", GenerateEd25519Key },
   { "genrsa", GenerateRSAKey },
   { "md5sum", MD5Sum },