Gopki

package pki

import (

   "crypto"
   "crypto/rand"
   "crypto/rsa"
   "crypto/sha256"
   "crypto/x509"
   "encoding/pem"
   "errors"

)

// GenerateKeyPair generates a new RSA public/private key pair. func GenerateKeyPair() (*rsa.PrivateKey, *rsa.PublicKey, error) {

   privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
   if err != nil {
       return nil, nil, err
   }
   publicKey := &privateKey.PublicKey
   return privateKey, publicKey, nil

}

// MarshalPrivateKeyPEM marshals an RSA private key to PEM format. func MarshalPrivateKeyPEM(privateKey *rsa.PrivateKey) ([]byte, error) {

   privateKeyBytes := x509.MarshalPKCS1PrivateKey(privateKey)
   privateKeyPEM := pem.EncodeToMemory(&pem.Block{
       Type:  "RSA PRIVATE KEY",
       Bytes: privateKeyBytes,
   })
   return privateKeyPEM, nil

}

// UnmarshalPrivateKeyPEM unmarshals an RSA private key from PEM format. func UnmarshalPrivateKeyPEM(privateKeyPEM []byte) (*rsa.PrivateKey, error) {

   block, _ := pem.Decode(privateKeyPEM)
   if block == nil || block.Type != "RSA PRIVATE KEY" {
       return nil, errors.New("failed to decode PEM block containing RSA private key")
   }
   privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
   if err != nil {
       return nil, err
   }
   return privateKey, nil

}

// Sign signs a message using an RSA private key. func Sign(privateKey *rsa.PrivateKey, message []byte) ([]byte, error) {

   hashed := sha256.Sum256(message)
   signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA256, hashed[:])
   if err != nil {
       return nil, err
   }
   return signature, nil

}

// Verify verifies a signature against a message using an RSA public key. func Verify(publicKey *rsa.PublicKey, message []byte, signature []byte) error {

   hashed := sha256.Sum256(message)
   err := rsa.VerifyPKCS1v15(publicKey, crypto.SHA256, hashed[:], signature)
   if err != nil {
       return err
   }
   return nil

}