package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"os"
)

func main() {
	var PKPW string
	flag.StringVar(&PKPW, "pp", PKPW, "private key passphrase")
	flag.Parse()
	// Read the standard input
	in, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatalf("input file: %s", err)
	}
	pemData, err := ioutil.ReadFile("pri.key")
	if err != nil {
		log.Fatalf("read key file: %s", err)
	}
	// Extract the PEM-encoded data block
	block, _ := pem.Decode(pemData)
	if block == nil {
		log.Fatalf("bad key data: %s", "not PEM-encoded")
	}
	if got, want := block.Type, "RSA PRIVATE KEY"; got != want {
		log.Fatalf("unknown key type %q, want %q", got, want)
	}
	if PKPW != "" {
		if decBlock, err := x509.DecryptPEMBlock(block, []byte(PKPW)); err != nil {
			log.Fatalf("error decrypting pem file: %s", err.Error())
		} else {
			block.Bytes = decBlock
		}
	}
	// Decode the RSA private key
	priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		log.Fatalf("bad private key: %s", err)
	}
	// Decrypt the data
	out, err := rsa.DecryptPKCS1v15(rand.Reader, priv, in)
	if err != nil {
		log.Fatalf("decrypt: %s", err)
	}
	// Write data to output file
	fmt.Fprint(os.Stdout, string(out))
}