Golang : Example for DSA(Digital Signature Algorithm) package functions
There are not many examples or tutorials out there on how to fully utilize the crypto/dsa
package. In this tutorial, we will learn how to utilize the crypto/dsa
functions to digitally sign our message and verify the signature.
This source code below will :
- generate a private key
- extract the public key from the generated private key
- use the private key to sign
- use the public key to verify the signature
dsaexample.go
package main
import (
"crypto/rand"
"crypto/dsa"
"crypto/md5"
"hash"
"fmt"
"os"
"io"
"math/big"
)
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)
// 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
}
An example output(note : public, private keys and signature values will be different each time the code is executed) :
Private Key :
{{{de735666a2220833b0b07f88c5ff30434e4af53f5e53c0e397057902a.....}
Public Key : {{de735666a2220833b0b07f88c5ff30434e4af53f5e53c0e397057902a......}
Signature :
75483cc98f4587b9ab4e8336b873e8eddd2fb41b594db267ce4bc09285ec15d63d17f6ec82989cd3
true
false
By Adam Ng
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