func decrypt(key *rsa.PrivateKey, ciphertext string) (string, error) {
cipherBytes, err := base64.StdEncoding.DecodeString(ciphertext)
if err != nil {
panic(err)
}
decrypted, err := key.Decrypt(rand.Reader, cipherBytes, crypto.SHA1.New())
if err != nil {
return "", err
}
return base64.StdEncoding.EncodeToString(decrypted), nil
}