Capture TLS Client Hello

capture_tls_clienthello.sh

#!/bin/sh

if [ -z "$1" ]; then
    echo "Usage: $0 example.com"
    exit 1
fi

CURL=curl
DOMAIN="$1"
BIN_FILE="tls_clienthello_$(echo $DOMAIN | sed 's/\./_/g').bin"

OUTPUT_DIR=''
[ ! -d "$OUTPUT_DIR" ] && OUTPUT_DIR=$(pwd)

BIN_FILE="${OUTPUT_DIR}/${BIN_FILE}"
PORT=4343

(nc -l -p $PORT > "$BIN_FILE") &

NC_PID=$!

$CURL -Isk "https://$DOMAIN" --connect-to ::127.0.0.1:$PORT -m 1

if [ -s "$BIN_FILE" ]; then
    echo "TLS Client Hello saved to $BIN_FILE"
else
    echo "Nothing was captured"
    rm -f "$BIN_FILE"
    kill $NC_PID
fi