rsa/cmd/keygen/keygen.go

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package keygen
import (
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"fmt"
"os"
"github.com/spf13/cobra"
"src.lwithers.me.uk/go/rsa/pkg/pemfile"
)
var (
bits int
pkcs1 bool
)
// Register the "keygen" subcommand.
func Register(root *cobra.Command) {
cmd := &cobra.Command{
Use: "keygen",
Short: "Generate a new private key and save to file",
Run: Keygen,
Args: cobra.ExactArgs(1),
}
cmd.Flags().IntVarP(&bits, "bits", "b", 3072, "Key size in bits")
cmd.Flags().BoolVarP(&pkcs1, "pkcs1", "", false, "Write key as PKCS#1 rather than PKCS#8")
root.AddCommand(cmd)
}
// Keygen will generate a new RSA private key and save it to a file.
func Keygen(cmd *cobra.Command, args []string) {
filename := args[0]
key, err := rsa.GenerateKey(rand.Reader, bits)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to generate new key (%d bits): %v\n", bits, err)
os.Exit(1)
}
// prepare DER-form data
var der []byte
if pkcs1 {
der = x509.MarshalPKCS1PrivateKey(key)
} else {
der, err = x509.MarshalPKCS8PrivateKey(key)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to marshal PKCS#8 private key: %v\n", err)
os.Exit(1)
}
}
// prepare PEM-form data
typ := pemfile.TypePKCS8PrivateKey
if pkcs1 {
typ = pemfile.TypePKCS1PrivateKey
}
x509raw := pem.EncodeToMemory(&pem.Block{
Type: typ,
Bytes: der,
})
// write to file
if err := os.WriteFile(filename, x509raw, 0600); err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}
}