initial commit

go.mod

@@ -0,0 +1,3 @@
+module go.balki.me/certinfo
+
+go 1.25.4

main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Fprintln(os.Stderr, "usage: inspect <cert.pem>")
+		os.Exit(2)
+	}
+	data, err := ioutil.ReadFile(os.Args[1])
+	if err != nil {
+		panic(err)
+	}
+
+	for {
+		var block *pem.Block
+		block, data = pem.Decode(data)
+		if block == nil {
+			break
+		}
+		if block.Type != "CERTIFICATE" {
+			continue
+		}
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "parse error: %v\n", err)
+			continue
+		}
+		fmt.Println("-----")
+		fmt.Printf("Subject: %s\n", cert.Subject.String())
+		fmt.Printf("Issuer: %s\n", cert.Issuer.String())
+		fmt.Printf("Serial: %s\n", cert.SerialNumber.String())
+		fmt.Printf("NotBefore: %s\n", cert.NotBefore)
+		fmt.Printf("NotAfter: %s\n", cert.NotAfter)
+		if len(cert.DNSNames) > 0 {
+			fmt.Printf("DNS SANs: %v\n", cert.DNSNames)
+		}
+		if len(cert.URIs) > 0 {
+			fmt.Printf("URI SANs: %v\n", cert.URIs)
+		}
+		fmt.Printf("Signature Algorithm: %s\n", cert.SignatureAlgorithm)
+		fmt.Printf("Public Key Algorithm: %s\n", cert.PublicKeyAlgorithm)
+	}
+}