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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/asn1"
"encoding/base64"
"encoding/pem"
"errors"
"fmt"
"io/ioutil"
"os"
"strings"
)
const KeyBitSize = 4096
func readFile(filename string) ([]byte, error) {
file, err := os.Open(filename)
if err != nil {
return nil, err
}
return ioutil.ReadAll(file)
}
func writeFile(filename string, data []byte) error {
file, err := os.Create(filename)
if err != nil {
return err
}
_, err = file.Write(data)
return err
}
func signData(data []byte, key *rsa.PublicKey) (string, error) {
based := base64.StdEncoding.EncodeToString(data)
h := sha256.Sum256([]byte(based))
dataHash := fmt.Sprintf("%x", h)
ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, key, []byte(dataHash))
if err != nil {
return "", err
}
signature := base64.StdEncoding.EncodeToString(ciphertext)
return fmt.Sprintf("%s.%s", based, signature), nil
}
func checkSignature(signedData string, key *rsa.PrivateKey) (bool, error) {
spl := strings.Split(signedData, ".")
data := spl[0]
signature := spl[1]
dataHash := fmt.Sprintf("%x", sha256.Sum256([]byte(data)))
decodedSign, err := base64.StdEncoding.DecodeString(signature)
if err != nil {
return false, err
}
signHash, err := decodeMessage(decodedSign, key)
if err != nil {
return false, err
}
return dataHash == string(signHash), nil
}
func encodeMessage(message []byte, key *rsa.PrivateKey) ([]byte, error) {
ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, &key.PublicKey, message)
if err != nil {
return nil, err
}
return ciphertext, nil
}
func decodeMessage(ciphertext []byte, key *rsa.PrivateKey) ([]byte, error) {
plaintext, err := rsa.DecryptPKCS1v15(rand.Reader, key, ciphertext)
if err != nil { return nil, err }
return plaintext, nil
}
func loadPublicPEM(filename string) (*rsa.PublicKey, error) {
pemBytes, err := readFile(filename)
if err != nil {
return nil, err
}
block, _ := pem.Decode(pemBytes)
if block == nil {
return nil, errors.New("there is no key in file")
}
return x509.ParsePKCS1PublicKey(block.Bytes)
}
func loadPrivatePEM(filename string) (*rsa.PrivateKey, error) {
pemBytes, err := readFile(filename)
if err != nil {
return nil, err
}
block, _ := pem.Decode(pemBytes)
if block == nil {
return nil, errors.New("there is no key in file")
}
return x509.ParsePKCS1PrivateKey(block.Bytes)
}
func generateKeys() (keys *rsa.PrivateKey, private []byte, public []byte, err error) {
key, err := rsa.GenerateKey(rand.Reader, KeyBitSize)
if err != nil {
return nil, nil, nil, err
}
var privateKey = &pem.Block{
Type: "PRIVATE KEY",
Bytes: x509.MarshalPKCS1PrivateKey(key),
}
asn1Bytes, _ := asn1.Marshal(key.PublicKey)
var publicKey = &pem.Block{
Type: "PUBLIC KEY",
Bytes: asn1Bytes,
}
bytePrivate := pem.EncodeToMemory(privateKey)
bytePublic := pem.EncodeToMemory(publicKey)
return key, bytePrivate, bytePublic, nil
}
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