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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/asn1"
"encoding/base64"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
)
const KeyBitSize = 4096
// Приватный ключ - отдаётся серверу
// Публичный ключ - сохраняется на клиенте
// Функции для подписи сообщений
func signRequest(req Request, key *rsa.PublicKey) (string, error) {
body, _ := json.Marshal(req)
based := base64.StdEncoding.EncodeToString(body)
h := sha256.Sum256([]byte(based))
requestHash := fmt.Sprintf("%x", h)
ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, key, []byte(requestHash))
if err != nil {
return "", nil
}
signature := base64.StdEncoding.EncodeToString(ciphertext)
return fmt.Sprintf("%s.%s", based, signature), nil
}
func parseKey(keyBytes []byte) (*rsa.PublicKey, error) {
block, _ := pem.Decode(keyBytes)
return x509.ParsePKCS1PublicKey(block.Bytes)
}
func generateKeys() (private []byte, public []byte, err error) {
key, err := rsa.GenerateKey(rand.Reader, KeyBitSize)
if err != nil {
return 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 bytePrivate, bytePublic, nil
}
// Функции для проверки подписи полученных сообщений
func decodeMessage(ciphertext []byte, stringKey string) ([]byte, error) {
block, _ := pem.Decode([]byte(stringKey))
if block == nil {
return nil, errors.New("key is not found in given string")
}
key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
return nil, err
}
plaintext, err := rsa.DecryptPKCS1v15(rand.Reader, key, ciphertext)
if err != nil {
return nil, err
}
return plaintext, err
}
func checkSignature(payload string, signature string, key string) (bool, error) {
h := sha256.Sum256([]byte(payload))
requestHash := fmt.Sprintf("%x", h)
decodedSign, err := base64.StdEncoding.DecodeString(signature)
if err != nil {
return false, err
}
signHash, err := decodeMessage(decodedSign, key)
if err != nil {
return false, err
}
return requestHash == string(signHash), nil
}
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