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-----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-----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)
}
See also : Golang : Generate DSA private, public key and PEM files example
By Adam Ng
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