Golang : Example for DSA(Digital Signature Algorithm) package functions



Tags : golang DSA

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



Tags : golang DSA

By Adam Ng

IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.


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