Golang : Generate DSA private, public key and PEM files example
For this tutorial, we will build on the previous tutorial on how to save private and public key files to learn how to generate DSA private, public key and PEM files.
Executing the code below will generate 3 files and output the DSA related data to screen.
package main
import (
"crypto/dsa"
"crypto/md5"
"crypto/rand"
"encoding/asn1"
"encoding/gob"
"encoding/pem"
"fmt"
"hash"
"io"
"math/big"
"os"
)
func main() {
params := new(dsa.Parameters)
// see http://golang.org/pkg/crypto/dsa/#ParameterSizes
if err := dsa.GenerateParameters(params, rand.Reader, dsa.L1024N160); err != nil {
fmt.Println(err)
os.Exit(1)
}
privatekey := new(dsa.PrivateKey)
privatekey.PublicKey.Parameters = *params
dsa.GenerateKey(privatekey, rand.Reader) // this generates a public & private key pair
var pubkey dsa.PublicKey
pubkey = privatekey.PublicKey
fmt.Println("Private Key :")
fmt.Printf("%x \n", privatekey)
fmt.Println("Public Key :")
fmt.Printf("%x \n", pubkey)
// save private and public key separately
privatekeyfile, err := os.Create("DSAprivate.key")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
privatekeyencoder := gob.NewEncoder(privatekeyfile)
privatekeyencoder.Encode(privatekey)
privatekeyfile.Close()
publickeyfile, err := os.Create("DSApublic.key")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
publickeyencoder := gob.NewEncoder(publickeyfile)
publickeyencoder.Encode(pubkey)
publickeyfile.Close()
// save DSA public key to PEM encoded file
pemfile, err := os.Create("DSApublickey.pem")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// http://golang.org/pkg/encoding/pem/#Block
// The decoded bytes of the contents. Typically a DER encoded ASN.1 structure.
asn1Bytes, err := asn1.Marshal(pubkey)
if err != nil {
fmt.Println(err)
os.Exit(1)
}
var pemkey = &pem.Block{
Type: "PUBLIC KEY",
Bytes: asn1Bytes}
err = pem.Encode(pemfile, pemkey)
if err != nil {
fmt.Println(err)
os.Exit(1)
}
pemfile.Close()
// ------------------------------
// below here is bonus
// Sign
var h hash.Hash
h = md5.New()
r := big.NewInt(0)
s := big.NewInt(0)
io.WriteString(h, "This is the message to be signed and verified!")
signhash := h.Sum(nil)
r, s, err = dsa.Sign(rand.Reader, privatekey, signhash)
if err != nil {
fmt.Println(err)
}
signature := r.Bytes()
signature = append(signature, s.Bytes()...)
fmt.Printf("Signature : %x\n", signature)
// Verify
verifystatus := dsa.Verify(&pubkey, signhash, r, s)
fmt.Println(verifystatus) // should be true
// we add additional data to change the signhash
io.WriteString(h, "This message is NOT to be signed and verified!")
signhash = h.Sum(nil)
verifystatus = dsa.Verify(&pubkey, signhash, r, s)
fmt.Println(verifystatus) // should be false
}
output of PEM file:
-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----
References :
https://www.socketloop.com/tutorials/golang-example-for-dsa-functions
https://www.socketloop.com/tutorials/golang-saving-private-and-public-key-to-files
See also : Golang : Example for DSA(Digital Signature Algorithm) package functions
By Adam Ng
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