add signing and verifying of messages

With this it is possible to sign a message with a private key and verify
it with a public key.
The only problem is, that it is currently not compatible with openssl
yet.

1 files changed, 73 insertions, 0 deletions

diff --git a/sign_input.go b/sign_input.go
new file mode 100644
index 0000000..4cd9035
--- /dev/null
+++ b/sign_input.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+  "crypto"
+  "crypto/rand"
+  "crypto/sha256"
+  "errors"
+  "flag"
+  "fmt"
+  "io"
+  "os"
+//  "crypto/ecdsa"
+//  "crypto/rsa"
+)
+
+type (
+  SignInputFlags struct {
+    Message        string // the message to sign
+    PrivateKeyPath string // path to the private key
+    Output         string // a path or stream to output the private key to
+
+    private_key crypto.Signer
+    output_stream io.Writer // the output stream for the CSR
+  }
+)
+
+func sign_input() {
+  flags := parse_sign_input_flags()
+  flags.private_key = load_private_key(flags.PrivateKeyPath)
+
+  output_stream, err := open_output_stream(flags.Output)
+  if err != nil {
+    crash_with_help(2, fmt.Sprintf("Error when creating file %s: %s", flags.Output, err))
+  }
+  flags.output_stream = output_stream
+  defer output_stream.Close()
+
+  if err := create_signature(flags); err != nil {
+    fmt.Fprintln(os.Stderr, "Error when creating signature", err)
+    os.Exit(3)
+  }
+}
+
+func parse_sign_input_flags() SignInputFlags {
+  flags := SignInputFlags{}
+  fs := flag.NewFlagSet("sign-input", flag.ExitOnError)
+  fs.StringVar(&flags.PrivateKeyPath, "private-key", "", "path to the private key file")
+  fs.StringVar(&flags.Output, "output", "STDOUT", "path where the generated signature should be stored")
+  fs.StringVar(&flags.Message, "message", "", "the message to sign")
+  fs.Parse(os.Args[2:])
+
+  return flags
+}
+
+func create_signature(flags SignInputFlags) error {
+  message := []byte(flags.Message)
+  // compute sha256 of the message
+  hash := sha256.New()
+  length, _ := hash.Write(message)
+  if length != len(message) { return errors.New("Error when creating hash over message!") }
+  fmt.Println(hash.Sum(nil))
+
+  // create signature of the hash using the private key
+  signature, err := flags.private_key.Sign(
+    rand.Reader,
+    hash.Sum([]byte("")),
+    nil,
+  )
+  if err != nil { return err }
+  fmt.Println(signature)
+  flags.output_stream.Write(signature)
+  return nil
+}