Rsa go

https://medium.com/@rafaelescrich/modern-cryptography-using-go-50e85f0f65af

package main
import (
    "crypto/rand"
    "crypto/rsa"
    "crypto/sha256"
    "fmt"
    "io"
    "os"
)
// RSA
const (
   rsaKeySize = 2048
)
type keypair struct {
    priv *rsa.PrivateKey
    pub  *rsa.PublicKey
}
var kp keypair
var ciphertext, signedMessage []byte
var rng io.Reader
func generateKeypair() error {
    var err error
    kp.priv, err = rsa.GenerateKey(rand.Reader, rsaKeySize)
    if err != nil {
        return err
    }
    kp.pub = &kp.priv.PublicKey
    return nil
}
func encrypt() {
    var err error
    secretMessage := []byte("This is the plaintext to be encrypted")
    label := []byte("mediumpost")
    ciphertext, err = rsa.EncryptOAEP(sha256.New(), rng, kp.pub,       secretMessage, label)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error from encryption: %s\n", err)
        return
    }
    // Since encryption is a randomized function, ciphertext will be
    // different each time.
    fmt.Printf("Ciphertext: %x\n", ciphertext)
}
func decrypt() {
    label := []byte("mediumpost")
    plaintext, err := rsa.DecryptOAEP(sha256.New(), rng, kp.priv, ciphertext, label)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error from decryption: %s\n", err)
        return
    }
    fmt.Printf("Plaintext: %s\n", string(plaintext))
}
func sign() {
    var err error
    message := []byte("This is the plaintext to be signed")
    signedMessage, err = rsa.EncryptPKCS1v15(rng, kp.pub, message)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error from encryption: %s\n", err)
        return
    }
    fmt.Printf("Signed Message: %x\n", signedMessage)
}
func verify() {
    msgVerified, err := rsa.DecryptPKCS1v15(rng, kp.priv, signedMessage)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error from decryption: %s\n", err)
        return
    }
    fmt.Printf("Verified Message: %s\n", string(msgVerified))
}
func main() {
    // crypto/rand.Reader is a good source of entropy for randomizing
    // encryption function.
    rng = rand.Reader
    // generates pair of keys
    generateKeypair()
    // encrypt message
    encrypt()
    // decrypt message
    decrypt()
    // sign message
    sign()
    // verify message
    verify()
}