Golang : Load ASN1 encoded DSA public key PEM file example

In this tutorial, we will learn how to get the DSA public key from a ASN1 encoded PEM file generated from previous tutorial. Pretty straight forward examples. Hope it helps!

From file :

 package main

 import (
 "bufio"
 "crypto/dsa"
 "encoding/asn1"
 "encoding/pem"
 "fmt"
 "os"
 )

 func main() {
 //load DSA PEM encoded public key file
 pemFile, err := os.Open("DSApublickey.pem")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // need to convert PEM file to []byte for decoding

 pemFileInfo, _ := pemFile.Stat()
 var size int64 = pemFileInfo.Size()
 pemBytes := make([]byte, size)

 // read pemFile content into pemBytes
 buffer := bufio.NewReader(pemFile)
 _, err = buffer.Read(pemBytes)

 // proper decoding now
 pemBlock, _ := pem.Decode([]byte(pemBytes))

 pemFile.Close()

 // convert PEM block to dsa.PublicKey
 // we use ASN1 because the PEM block was encoded with ASN1
 // see https://www.socketloop.com/tutorials/golang-generate-dsa-private-public-key-and-pem-files-example

 // if the PEM block is not encoded by ASN1, the unmarshal will fail
 // you need to find out the Public Key algorithm used to encode the PEM bytes

 var publicKey dsa.PublicKey

 _, err = asn1.Unmarshal(pemBlock.Bytes, &publicKey)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 //fmt.Printf("Public key : \n%x\n", publicKey)

 fmt.Printf("Public key parameter P: %v\n", publicKey.Parameters.P)
 fmt.Printf("Public key parameter Q: %v\n", publicKey.Parameters.Q)
 fmt.Printf("Public key parameter G: %v\n", publicKey.Parameters.G)
 fmt.Printf("Public key Y: %v\n", publicKey.Y)

 }

and from PEM block :

 package main

 import (
 "crypto/dsa"
 "encoding/asn1"
 "encoding/pem"
 "fmt"
 "os"
 )

 func main() {

 var pemBytes = `
 -----BEGIN PUBLIC KEY-----
 MIIBpjCCAR4CgYEA1cKOQUxDRqRHt8yR5vfEunyFB6pblE9W/fyaJHgpWMzkvSHX
 mZvDhN5huH3OM0vC5Y8UbfyplET3x/HfXUbDUgk4bT0CrWHmrANMjdPgStZF+nWP
 Yfa6QUyVbRZumI6iBaCH63107scE8tygmwSW3n1jYLoSv6VItDEiBIdoK18CFQC6
 q4LlyX4YZblOKYw8CFyPShtcAwKBgHAN+TWyUhqCVZmwUdH3pJelT4iT9vkg4NLn
 1h+qJJ1XU+OILAAeuO3z8vLMIpeFaDL5CvUb7S0vSqx2EFj/G67aH9nL0MwtXjn7
 SCy4EOF5dlHbafXj4PnPrvo3/Mr+3a2i5lenlhyyb1Vnd/0VcrGwWleAfDBuGdYu
 S5WCYAj3AoGBAMDl+N8XI3LBi/LUQbi9di0tvA/2t+c6UZTT/CDTkyDucFNEeqWI
 sdOsf+hIbI8pEy81y6yBc50wcf1uqcZxovKsZbuv8vS3NBPaeOT7l6ltYdNxzg/7
 QFfi3qQXXLONWYXW4diWaZu6Kq5XvhfWkoUdGzGiD84UVW7jmeDy/Px6
 -----END PUBLIC KEY-----
 `

 // proper decoding now
 pemBlock, _ := pem.Decode([]byte(pemBytes))

 // convert PEM block to dsa.PublicKey
 // we use ASN1 because the PEM block was encoded with ASN1
 // see https://www.socketloop.com/tutorials/golang-generate-dsa-private-public-key-and-pem-files-example

 // if the PEM block is not encoded by ASN1, the unmarshal will fail
 // you need to find out the Public Key algorithm used to encode the PEM bytes

 var publicKey dsa.PublicKey

 _, err := asn1.Unmarshal(pemBlock.Bytes, &publicKey)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 //fmt.Printf("Public key : \n%x\n", publicKey)

 fmt.Printf("Public key parameter P: %v\n", publicKey.Parameters.P)
 fmt.Printf("Public key parameter Q: %v\n", publicKey.Parameters.Q)
 fmt.Printf("Public key parameter G: %v\n", publicKey.Parameters.G)
 fmt.Printf("Public key Y: %v\n", publicKey.Y)

 }