From 8fd2e769394890f2e22ccf049e5fa04d9f8f1706 Mon Sep 17 00:00:00 2001
From: Kyle Isom <coder@kyleisom.net>
Date: Thu, 14 Jan 2016 17:29:55 -0800
Subject: [PATCH] Add certverify utility.

---
 README.md              |  1 +
 cmd/certverify/README  | 36 +++++++++++++++++
 cmd/certverify/main.go | 89 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+)
 create mode 100644 cmd/certverify/README
 create mode 100644 cmd/certverify/main.go

diff --git a/README.md b/README.md
index 454835c..43c85ce 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,7 @@ Contents:
         certchain/  Display the certificate chain from a
                     TLS connection.
         certdump/   Dump certificate information.
+	certverify/ Verify a TLS X.509 certificate.
 	clustersh/  Run commands or transfer files across multiple
                     servers via SSH.
         csrpubdump/ Dump the public key from an X.509
diff --git a/cmd/certverify/README b/cmd/certverify/README
new file mode 100644
index 0000000..66cdc4b
--- /dev/null
+++ b/cmd/certverify/README
@@ -0,0 +1,36 @@
+certverify
+
+This is a small utility to verify a TLS X.509 certificate. It returns
+0 on success; on error, it prints the error and returns with exit code 1.
+It does not check for revocations (though this is a planned feature),
+and it does not check the hostname (it deals only in certificate files).
+
+[ Usage ]
+	certverify [-ca bundle] [-f] [-i bundle] [-v] certificate
+
+[ Flags ]
+	-ca bundle	Specify the path to the CA certificate bundle
+			to use.
+	-f		Force the use of the intermediate bundle, ignoring
+			any intermediates bundled with the certificate.
+	-i bundle	Specify the path to the intermediate certificate
+			bundle to use.
+	-v		Print extra information during the program's run.
+			If the certificate validates, also prints 'OK'.
+
+[ Examples ]
+
+To verify the 'www.pem' certificate against the system roots:
+
+	$ certverify www.pem
+	$ echo $?
+	0
+
+To verify the 'www.pem' certificate against the 'ca-cert.pem' CA
+certificate bundle, and seeing a mismatch:
+
+	$ certverify -ca ca-cert.pem www.pem
+	Verification failed: x509: certificate signed by unknown authority
+	$ echo $?
+	1
+
diff --git a/cmd/certverify/main.go b/cmd/certverify/main.go
new file mode 100644
index 0000000..c1d9b69
--- /dev/null
+++ b/cmd/certverify/main.go
@@ -0,0 +1,89 @@
+package main
+
+import (
+	"crypto/x509"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/cloudflare/cfssl/helpers"
+	"github.com/kisom/die"
+	"github.com/kisom/goutils/lib"
+)
+
+func main() {
+	var caFile, intFile string
+	var forceIntermediateBundle, verbose bool
+	flag.StringVar(&caFile, "ca", "", "CA certificate `bundle`")
+	flag.StringVar(&intFile, "i", "", "intermediate `bundle`")
+	flag.BoolVar(&forceIntermediateBundle, "f", false,
+		"force the use of the intermediate bundle, ignoring any intermediates bundled with certificate")
+	flag.BoolVar(&verbose, "v", false, "verbose")
+	flag.Parse()
+
+	var roots *x509.CertPool
+	if caFile != "" {
+		var err error
+		if verbose {
+			fmt.Println("[+] loading root certificates from", caFile)
+		}
+		roots, err = helpers.LoadPEMCertPool(caFile)
+		die.If(err)
+	}
+
+	var ints *x509.CertPool
+	if intFile != "" {
+		var err error
+		if verbose {
+			fmt.Println("[+] loading intermediate certificates from", intFile)
+		}
+		ints, err = helpers.LoadPEMCertPool(caFile)
+		die.If(err)
+	} else {
+		ints = x509.NewCertPool()
+	}
+
+	if flag.NArg() != 1 {
+		fmt.Fprintf(os.Stderr, "Usage: %s [-ca bundle] [-i bundle] cert",
+			lib.ProgName())
+	}
+
+	fileData, err := ioutil.ReadFile(flag.Arg(0))
+	die.If(err)
+
+	chain, err := helpers.ParseCertificatesPEM(fileData)
+	die.If(err)
+	if verbose {
+		fmt.Printf("[+] %s has %d certificates\n", flag.Arg(0), len(chain))
+	}
+
+	cert := chain[0]
+	if len(chain) > 1 {
+		if !forceIntermediateBundle {
+			for _, intermediate := range chain[1:] {
+				if verbose {
+					fmt.Printf("[+] adding intermediate with SKI %x\n", intermediate.SubjectKeyId)
+				}
+
+				ints.AddCert(intermediate)
+			}
+		}
+	}
+
+	opts := x509.VerifyOptions{
+		Intermediates: ints,
+		Roots:         roots,
+		KeyUsages:     []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
+	}
+
+	_, err = cert.Verify(opts)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Verification failed: %v\n", err)
+		os.Exit(1)
+	}
+
+	if verbose {
+		fmt.Println("OK")
+	}
+}