RSA Digital Signature

package main

import (
	"crypto/rsa"
	"crypto/rand"
	"crypto/x509"
	"os"
	"encoding/pem"
	"crypto"
	"crypto/sha256"
	"fmt"
)

func rsaGenKey(publicPath string,privatePath string,bits int) error {
	privateKey,err:=rsa.GenerateKey(rand.Reader,bits)
	if err!=nil {
		return err
	}
	privateKeyStream:=x509.MarshalPKCS1PrivateKey(privateKey)
	privateFile,err:=os.Create(privatePath)
	if err!=nil {
		return err
	}
	defer privateFile.Close()
	err=pem.Encode(privateFile,&pem.Block{
		Type:"RSA Private Key",
		Bytes:privateKeyStream,
	})
	if err!=nil {
		return err
	}
	publicKey:=privateKey.PublicKey
	publicKeyStream:=x509.MarshalPKCS1PublicKey(&publicKey)
	publicFile,err:=os.Create(publicPath)
	if err!=nil {
		return err
	}
	defer publicFile.Close()
	err=pem.Encode(publicFile,&pem.Block{
		Type:"RSA Public Key",
		Bytes:publicKeyStream,
	})
	if err!=nil {
		return err
	}
	return nil
}

func signature(x string,privatePath string) ([]byte,error) {
	privateFile,err:=os.Open(privatePath)
	if err!=nil {
		return nil,err
	}
	defer privateFile.Close()
	fileinfo,err:=os.Stat(privatePath)
	if err!=nil {
		return nil,err
	}
	m:=make([]byte,fileinfo.Size())
	privateFile.Read(m)
	block,_:=pem.Decode(m)
	privateKey,err:=x509.ParsePKCS1PrivateKey(block.Bytes)
	if err!=nil {
		return nil,err
	}
	mhash:=sha256.New()
	mhash.Write([]byte(x))
	y:=mhash.Sum(nil)
	z,err:=rsa.SignPKCS1v15(rand.Reader,privateKey,crypto.SHA256,y)
	if err!=nil {
		return nil,err
	}
	return z,nil
}

func verify(x string,publicPath string,src []byte) error {
	publicFile,err:=os.Open(publicPath)
	if err!=nil {
		return err
	}
	defer publicFile.Close()
	fileinfo,err:=os.Stat(publicPath)
	if err!=nil {
		return err
	}
	m:=make([]byte,fileinfo.Size())
	publicFile.Read(m)
	block,_:=pem.Decode(m)
	if err!=nil {
		return err
	}
	publicKey,err:=x509.ParsePKCS1PublicKey(block.Bytes)
	if err!=nil {
		return err
	}
	mhash:=sha256.New()
	mhash.Write([]byte(x))
	y:=mhash.Sum(nil)
	err=rsa.VerifyPKCS1v15(publicKey,crypto.SHA256,y,src)
	if err!=nil {
		return err
	}
	return nil
}

func main()  {
	privatePath:="private181115.pem"
	publicPath:="public181115.pem"
	err:=rsaGenKey(publicPath,privatePath,3072)
	if err!=nil {
		fmt.Print(err)
		return
	}
	x1:="anti-collectivism"
	z,err:=signature(x1,privatePath)
	if err!=nil {
		fmt.Print(err)
		return
	}
	x2:="anti-collectivism"
	err=verify(x2,publicPath,z)
	if err!=nil {
		fmt.Print(err)
		return
	}
	fmt.Print("ok")
}