add verification of messages

This commit adds back the possibility to verify a message through a
public key and a signature. It works a little bit different than before
as it always prints the base64 version, but it makes it easier to use.

3 files changed, 78 insertions, 10 deletions

diff --git a/flags.go b/flags.go
index 9af8371..c825b57 100644
--- a/flags.go
+++ b/flags.go
@@ -5,6 +5,7 @@ package main
 
 import (
   "crypto/elliptic"
+  "encoding/base64"
   "flag"
   "fmt"
   "io"
@@ -48,13 +49,17 @@ type (
     publicKeyPath    string // path to the public key
     signRequestPath  string // path to the certificate sign request
     certificateFlags *certFlagsContainer // container for certificate related flags
+    signature        string // a base64 encoded signature
   }
 
   // a container for the refined flags
   flagSet struct {
     PrivateKey pki.PrivateKey
+    PublicKey  pki.PublicKey
     Output     io.WriteCloser
     Input      io.ReadCloser
+    // an asn1 encoded signature of a signage process
+    Signature  []byte
 
     // private key specific stuff
     PrivateKeyGenerationFlags privateKeyGenerationFlags
@@ -140,6 +145,22 @@ func (f *Flags) parsePrivateKey() error {
   return nil
 }
 
+// add the public key flag
+func (f *Flags) AddPublicKey() {
+  f.check_list = append(f.check_list, f.parsePublicKey)
+  f.flagset.StringVar(&f.flag_container.publicKeyPath, "public-key", "", "path to the public key")
+}
+
+// parse public key flag
+func (f *Flags) parsePublicKey() error {
+  if f.flag_container.publicKeyPath == "" { return fmt.Errorf("No public key given!") }
+
+  pu, err := ReadPublicKeyFile(f.flag_container.publicKeyPath)
+  if err != nil { return fmt.Errorf("Error reading public key: %s", err) }
+  f.Flags.PublicKey = pu
+  return nil
+}
+
 // add the output parameter to the checklist
 func (f *Flags) AddOutput() {
   f.check_list = append(f.check_list, f.parseOutput)
@@ -214,3 +235,17 @@ func (f *Flags) parsePrivateKeyGenerationFlags() error {
   }
   return nil
 }
+
+// add the signature flag to load a signature from a signing process
+func (f *Flags) AddSignature() {
+  f.check_list = append(f.check_list, f.parseSignature)
+  f.flagset.StringVar(&f.flag_container.signature, "signature", "", "the base64 encoded signature to use for verification")
+}
+
+// parse the signature flag
+func (f *Flags) parseSignature() error {
+  var err error
+  f.Flags.Signature, err = base64.StdEncoding.DecodeString(f.flag_container.signature)
+  if err != nil { return err }
+  return nil
+}
diff --git a/main.go b/main.go
index 3898417..c509fd7 100644
--- a/main.go
+++ b/main.go
@@ -24,7 +24,7 @@ func main() {
   case "create-private":   create_private_key()
   case "create-public":    create_public_key()
   case "sign-input":       sign_input()
-//  case "verify-signature": verify_signature()
+  case "verify-signature": verify_input()
 //  case "create-cert-sign": create_sign_request()
 //  case "sign-request":     sign_request()
   case "help":             print_modules()
@@ -73,8 +73,8 @@ func create_public_key() {
 func sign_input() {
   fs := NewFlags("sign-input")
   fs.AddPrivateKey()
-  fs.AddOutput()
   fs.AddInput()
+  fs.AddOutput()
   err := fs.Parse(program_args())
   if err != nil { os.Exit(2) }
 
@@ -92,6 +92,29 @@ func sign_input() {
   }
 }
 
+// verify a message using a signature and a public key
+func verify_input() {
+  fs := NewFlags("sign-input")
+  fs.AddPublicKey()
+  fs.AddInput()
+  fs.AddOutput()
+  fs.AddSignature()
+  err := fs.Parse(program_args())
+  if err != nil { os.Exit(2) }
+
+  signature := fs.Flags.Signature
+  message, err := ioutil.ReadAll(fs.Flags.Input)
+  if err != nil { crash_with_help(2, "Error reading input: %s", err) }
+  valid, err := fs.Flags.PublicKey.Verify(message, signature, crypto.SHA256)
+  if err != nil { crash_with_help(2, "Could not verify message with signature: %s", err) }
+  if valid {
+    fmt.Println("valid")
+    os.Exit(0)
+  }
+  fmt.Println("invalid")
+  os.Exit(1)
+}
+
 // print the module help
 func print_modules() {
   fmt.Printf(`Usage: %s command args
@@ -110,7 +133,7 @@ where 'command' is one of:
 
 // crash and provide a helpful message
 func crash_with_help(code int, message string, args ...interface{}) {
-  fmt.Fprintln(os.Stderr, message)
+  fmt.Fprintf(os.Stderr, message + "\n", args...)
   print_modules()
   os.Exit(code)
 }
diff --git a/private_key.go b/private_key.go
index 3e6aee3..0591e18 100644
--- a/private_key.go
+++ b/private_key.go
@@ -5,25 +5,22 @@ import (
   "github.com/gibheer/pki"
 )
 
-const (
-  TypeLabelRSA   = "RSA PRIVATE KEY"
-  TypeLabelECDSA = "EC PRIVATE KEY"
-)
-
 var (
   ErrNoPKFound = errors.New("no private key found")
+  ErrNoPUFound = errors.New("no public key found")
+  ErrUnknownFormat = errors.New("key is an unknown format")
 )
 
 // Read the private key from the path and try to figure out which type of key it
 // might be.
 func ReadPrivateKeyFile(path string) (pki.PrivateKey, error) {
-  raw_pk, err := readSectionFromFile(path, TypeLabelECDSA)
+  raw_pk, err := readSectionFromFile(path, pki.PemLabelEcdsa)
   if err == nil {
     pk, err := pki.LoadPrivateKeyEcdsa(raw_pk)
     if err != nil { return nil, err }
     return pk, nil
   }
-  raw_pk, err = readSectionFromFile(path, TypeLabelRSA)
+  raw_pk, err = readSectionFromFile(path, pki.PemLabelRsa)
   if err == nil {
     pk, err := pki.LoadPrivateKeyRsa(raw_pk)
     if err != nil { return nil, err }
@@ -31,3 +28,16 @@ func ReadPrivateKeyFile(path string) (pki.PrivateKey, error) {
   }
   return nil, ErrNoPKFound
 }
+
+// read the public key and try to figure out what kind of key it might be
+func ReadPublicKeyFile(path string) (pki.PublicKey, error) {
+  raw_pu, err := readSectionFromFile(path, pki.PemLabelPublic)
+  if err != nil { return nil, ErrNoPUFound }
+
+  var public pki.PublicKey
+  public, err = pki.LoadPublicKeyEcdsa(raw_pu)
+  if err == nil { return public, nil }
+  public, err = pki.LoadPublicKeyRsa(raw_pu)
+  if err == nil { return public, nil }
+  return nil, ErrUnknownFormat
+}