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I have seems working way how to verify the signature with mbedtls on ESP32. Now I need to verify the same signature with NodeJS but I had no success with it.

mbedtls example:

#include "mbedtls/base64.h"
#include "mbedtls/pk.h"
#include <string.h>

unsigned char hard_base_signature[6000] =
    "Y59Z0Jg1WCKKMpKuGYW5nLsyDgPU3eoMwtLd74lejj6bWr2lPh5MKzcfXE18s6L7YG7yB18WNW"
    "/meh2KAegHEDZKqy2OHf0n7bKz17OSIcoSgI9N4Eu116naVtqO5vwYJ3JGqE625JkuQza4sLZh"
    "ccosbd+mNLUEBN7sr+BtlY1rU0hed56GbP6iJ+8x5XEW4HBUQ1ATQQGNu5QtqgBA+"
    "jv8TktXlOVJ8XXKkOUUmVu1NU1TX+hXgNqZC6drtg5+"
    "UtaMS77eF5qctMXyNKTqJ9UGTi1S0pg3TJoVCI7A8M6GLuEsvZ0gNyDDhjY73mR2KtXknEEA4E"
    "TfGS1xG0SE7g==";

unsigned char public_key_content[6000] =
    "-----BEGIN PUBLIC KEY-----\n"
    "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0YbMPv02Danre1OGkkkR\n"
    "F093SREmgsZG/o+3oDYIGm8aLESt94GGdJzd97R+usprFtnKRDoo0eICAVY1NiIi\n"
    "m9840J9+q6MOlQJlvxQy1A3+K1Vg/XsEwRTNOR3yweC6KdVeD5ITKn4nNNBdhUdu\n"
    "fR80DOK7i4RjNVwYAzGYiwrkcMgBVu8BVKl/P0712Gi/58yAat9qfOvn8Q6rsy3T\n"
    "8YGS24KCN6xQPBt+bNXnMDBwxlzky7N2rfiv3Zid0R32PivBNCsNQmK+SP0zyJ2h\n"
    "TmI6VQ4GSBObfgK4dnaDfGlHfR1RNapzpd/PfdYw4XSjDF98IQJqyd83MjTXQK+a\n"
    "UwIDAQAB\n"
    "-----END PUBLIC KEY-----\n\0";

void app_main() {
  int ret = 0;
  /*
   * Read the RSA public key
   */
  mbedtls_pk_context pk_public;
  mbedtls_pk_init(&pk_public);
  if ((ret = mbedtls_pk_parse_public_key(&pk_public, public_key_content,
                                         strlen((char *)public_key_content) +
                                             1) != 0)) {
    printf("failed: %d\n", ret);
    return;
  }
  unsigned char correct_message[] = "This is a test..";
  unsigned char incorrect_message[] = "This is a test!!";

  static unsigned char hard_signature[6000];

  size_t hard_signature_len = 0;

  mbedtls_base64_decode(hard_signature, 6000, &hard_signature_len,
                        hard_base_signature,
                        strlen((char *)hard_base_signature));

  printf("Verify result 1: %d\n",
         mbedtls_pk_verify(&pk_public, MBEDTLS_MD_MD5, correct_message,
                           strlen((char *)correct_message), hard_signature,
                           hard_signature_len)); // <- Verify result 1: 0

  printf("Verify result 2: %d\n",
         mbedtls_pk_verify(&pk_public, MBEDTLS_MD_MD5, incorrect_message,
                           strlen((char *)incorrect_message), hard_signature,
                           hard_signature_len)); // <- Verify result 2: -17280
}

NodeJS example:

import crypto from "crypto";
import { TextEncoder } from "util";

const publicKeyContent =
  "-----BEGIN PUBLIC KEY-----\n" +
  "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0YbMPv02Danre1OGkkkR\n" +
  "F093SREmgsZG/o+3oDYIGm8aLESt94GGdJzd97R+usprFtnKRDoo0eICAVY1NiIi\n" +
  "m9840J9+q6MOlQJlvxQy1A3+K1Vg/XsEwRTNOR3yweC6KdVeD5ITKn4nNNBdhUdu\n" +
  "fR80DOK7i4RjNVwYAzGYiwrkcMgBVu8BVKl/P0712Gi/58yAat9qfOvn8Q6rsy3T\n" +
  "8YGS24KCN6xQPBt+bNXnMDBwxlzky7N2rfiv3Zid0R32PivBNCsNQmK+SP0zyJ2h\n" +
  "TmI6VQ4GSBObfgK4dnaDfGlHfR1RNapzpd/PfdYw4XSjDF98IQJqyd83MjTXQK+a\n" +
  "UwIDAQAB\n" +
  "-----END PUBLIC KEY-----\n";

const signature =
  "Y59Z0Jg1WCKKMpKuGYW5nLsyDgPU3eoMwtLd74lejj6bWr2lPh5MKzcfXE18s6L7YG7yB18WNW" +
  "/meh2KAegHEDZKqy2OHf0n7bKz17OSIcoSgI9N4Eu116naVtqO5vwYJ3JGqE625JkuQza4sLZh" +
  "ccosbd+mNLUEBN7sr+BtlY1rU0hed56GbP6iJ+8x5XEW4HBUQ1ATQQGNu5QtqgBA+" +
  "jv8TktXlOVJ8XXKkOUUmVu1NU1TX+hXgNqZC6drtg5+" +
  "UtaMS77eF5qctMXyNKTqJ9UGTi1S0pg3TJoVCI7A8M6GLuEsvZ0gNyDDhjY73mR2KtXknEEA4E" +
  "TfGS1xG0SE7g==";
const publicKey = crypto.createPublicKey({
  key: publicKeyContent,
  type: "spki",
  format: "pem",
});

console.log(
  "Verify result 1:",
  crypto.verify(
    "RSA-MD5",
    new TextEncoder().encode("This is a test.."),
    publicKey,
    Buffer.from(signature, "base64")
  )
); // <- Verify result 1: false

console.log(
  "Verify result 2:",
  crypto.verify(
    "MD5",
    new TextEncoder().encode("This is a test.."),
    publicKey,
    Buffer.from(signature, "base64")
  )
); // <- Verify result 2: false

I think the issue with md5 digest - I miss it somewhere. Unfortunately, I'm very new in crypto things. Could you help me and point on my mistake. Thanks!

Brainenjii
  • 1
  • 2
  • 1
    The signature is not PKCS#1 compliant. After decryption without removing the padding the signature is hex encoded `0001ff...ff003020300c06082a864886f70d02050500041054686973206973206120746573742e2e`. Here `3020300c06082a864886f70d020505000410` corresponds to the digest MD5 used (s. [RFC8017, p. 47](https://datatracker.ietf.org/doc/html/rfc8017#page-47)), but `54686973206973206120746573742e2e` is not the MD5 hash of the plaintext (as it should be), but the plaintext itself. So the problem is in the code that computes the signature. – Topaco Nov 17 '21 at 08:19
  • @Topaco Thx a lot, it mostly works now! At least, if I sign md5 hash received from nodejs it's able to verify it! – Brainenjii Nov 18 '21 at 04:52

0 Answers0