cmd: add tlsinfo.

cmd/tlsinfo/main.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"os"
+)
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Printf("Usage: %s ‹hostname:port>\n", os.Args[0])
+		os.Exit(1)
+	}
+
+	hostPort := os.Args[1]
+	conn, err := tls.Dial("tcp", hostPort, &tls.Config{
+		InsecureSkipVerify: true,
+	})
+
+	if err != nil {
+		fmt.Printf("Failed to connect to the TLS server: %v\n", err)
+		os.Exit(1)
+	}
+	defer conn.Close()
+	state := conn.ConnectionState()
+	printConnectionDetails(state)
+}
+
+func printConnectionDetails(state tls.ConnectionState) {
+	version := tlsVersion(state.Version)
+	cipherSuite := tls.CipherSuiteName(state.CipherSuite)
+	fmt.Printf("TLS Version: %s\n", version)
+	fmt.Printf("Cipher Suite: %s\n", cipherSuite)
+	printPeerCertificates(state.PeerCertificates)
+}
+
+func tlsVersion(version uint16) string {
+	switch version {
+
+	case tls.VersionTLS13:
+		return "TLS 1.3"
+	case tls.VersionTLS12:
+
+		return "TLS 1.2"
+	case tls.VersionTLS11:
+		return "TLS 1.1"
+	case tls.VersionTLS10:
+		return "TLS 1.0"
+	default:
+		return "Unknown"
+	}
+}
+
+func printPeerCertificates(certificates []*x509.Certificate) {
+	for i, cert := range certificates {
+		fmt.Printf("Certificate %d\n", i+1)
+		fmt.Printf("\tSubject: %s\n", cert.Subject)
+		fmt.Printf("\tIssuer: %s\n", cert.Issuer)
+		fmt.Printf("\tDNS Names:	%v\n", cert.DNSNames)
+		fmt.Printf("\tNot Before: %s\n:", cert.NotBefore)
+		fmt.Printf("\tNot After: %s\n", cert.NotAfter)
+	}
+}