Added first step to Enterprise Attestation.

Once enabled, it allows to generate a CSR in the device, which is sent to our PKI. If valid, it returns a signed certificate by an intermediate CA that will be used for attestation.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

src/fido/cbor_vendor.c

@@ -26,6 +26,7 @@
 #include "mbedtls/ecdh.h"
 #include "mbedtls/chachapoly.h"
 #include "mbedtls/hkdf.h"
+#include "mbedtls/x509_csr.h"
 
 extern uint8_t keydev_dec[32];
 extern bool has_keydev_dec;
@@ -226,6 +227,45 @@ int cbor_vendor_generic(uint8_t cmd, const uint8_t *data, size_t len) {
         has_keydev_dec = true;
         goto err;
     }
+    else if (cmd == CTAP_VENDOR_EA) {
+        if (vendorCmd == 0x01) {
+            uint8_t buffer[1024];
+            mbedtls_ecdsa_context ekey;
+            mbedtls_ecdsa_init(&ekey);
+            int ret = mbedtls_ecp_read_key(MBEDTLS_ECP_DP_SECP256R1, &ekey, file_get_data(ef_keydev), file_get_size(ef_keydev));
+            if (ret != 0) {
+                mbedtls_ecdsa_free(&ekey);
+                CBOR_ERROR(CTAP2_ERR_PROCESSING);
+            }
+            ret = mbedtls_ecp_mul(&ekey.grp, &ekey.Q, &ekey.d, &ekey.grp.G, random_gen, NULL);
+            if (ret != 0) {
+                mbedtls_ecdsa_free(&ekey);
+                CBOR_ERROR(CTAP2_ERR_PROCESSING);
+            }
+            pico_unique_board_id_t rpiid;
+            pico_get_unique_board_id(&rpiid);
+            mbedtls_x509write_csr ctx;
+            mbedtls_x509write_csr_init(&ctx);
+            snprintf((char *)buffer, sizeof(buffer), "C=ES,O=Pico Keys,OU=Authenticator Attestation,CN=Pico Fido EE Serial %llu", ((uint64_t)rpiid.id[0] << 56) | ((uint64_t)rpiid.id[1] << 48) | ((uint64_t)rpiid.id[2] << 40) | ((uint64_t)rpiid.id[3] << 32) | (rpiid.id[4] << 24) | (rpiid.id[5] << 16) | (rpiid.id[6] << 8) | rpiid.id[7]);
+            mbedtls_x509write_csr_set_subject_name(&ctx, (char *)buffer);
+            mbedtls_pk_context key;
+            mbedtls_pk_init(&key);
+            mbedtls_pk_setup(&key, mbedtls_pk_info_from_type(MBEDTLS_PK_ECKEY));
+            key.pk_ctx = &ekey;
+            mbedtls_x509write_csr_set_key(&ctx, &key);
+            mbedtls_x509write_csr_set_md_alg(&ctx, MBEDTLS_MD_SHA256);
+            mbedtls_x509write_csr_set_extension(&ctx, "\x2B\x06\x01\x04\x01\x82\xE5\x1C\x01\x01\x04", 0xB, 0, aaguid, sizeof(aaguid));
+            ret = mbedtls_x509write_csr_der(&ctx, buffer, sizeof(buffer), random_gen, NULL);
+            mbedtls_ecdsa_free(&ekey);
+            if (ret <= 0) {
+                mbedtls_x509write_csr_free(&ctx);
+                CBOR_ERROR(CTAP2_ERR_PROCESSING);
+            }
+            CBOR_CHECK(cbor_encoder_create_map(&encoder, &mapEncoder, 1));
+            CBOR_CHECK(cbor_encode_uint(&mapEncoder, 0x01));
+            CBOR_CHECK(cbor_encode_byte_string(&mapEncoder, buffer + sizeof(buffer) - ret, ret));
+        }
+    }
     else
         CBOR_ERROR(CTAP2_ERR_UNSUPPORTED_OPTION);
     CBOR_CHECK(cbor_encoder_close_container(&encoder, &mapEncoder));

src/fido/ctap.h

@@ -124,6 +124,7 @@ typedef struct {
 #define CTAP_VENDOR_BACKUP              0x01
 #define CTAP_VENDOR_MSE                 0x02
 #define CTAP_VENDOR_UNLOCK              0x03
+#define CTAP_VENDOR_EA                  0x04
 
 #define CTAP_PERMISSION_MC              0x01  // MakeCredential
 #define CTAP_PERMISSION_GA              0x02  // GetAssertion

tools/pico-fido-tool.py

@@ -27,6 +27,8 @@ from words import words
 from threading import Event
 from typing import Mapping, Any, Optional, Callable
 import struct
+import urllib.request
+import json
 from enum import IntEnum, unique
 
 try:
@@ -48,6 +50,7 @@ try:
     from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat
     from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
     from cryptography.hazmat.primitives import hashes
+    from cryptography import x509
 except:
     print('ERROR: cryptography module not found! Install cryptography package.\nTry with `pip install cryptography`')
     sys.exit(-1)
@@ -63,6 +66,21 @@ else:
     print('ERROR: platform not supported')
     sys.exit(-1)
 
+def get_pki_data(url, data=None, method='GET'):
+    user_agent = 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; '
+    'rv:1.9.0.7) Gecko/2009021910 Firefox/3.0.7'
+    method = 'GET'
+    if (data is not None):
+        method = 'POST'
+    req = urllib.request.Request(f"https://www.picokeys.com/pico/pico-fido/{url}/",
+                                method=method,
+                                data=data,
+                                headers={'User-Agent': user_agent, })
+    response = urllib.request.urlopen(req)
+    resp = response.read().decode('utf-8')
+    j = json.loads(resp)
+    return j
+
 class VendorConfig(Config):
 
     class PARAM(IntEnum):
@@ -179,6 +197,7 @@ class Vendor:
         VENDOR_BACKUP    = 0x01
         VENDOR_MSE       = 0x02
         VENDOR_UNLOCK    = 0x03
+        VENDOR_CSR       = 0x04
 
     @unique
     class PARAM(IntEnum):
@@ -189,6 +208,7 @@ class Vendor:
         ENABLE              = 0x01
         DISABLE             = 0x02
         KEY_AGREEMENT       = 0x01
+        CSR                 = 0x01
 
     class RESP(IntEnum):
         PARAM       = 0x01
@@ -342,6 +362,12 @@ class Vendor:
     def disable_device_aut(self):
         self.vcfg.disable_device_aut()
 
+    def csr(self):
+        return self._call(
+            Vendor.CMD.VENDOR_CSR,
+            Vendor.SUBCMD.CSR,
+        )
+
 def parse_args():
     parser = argparse.ArgumentParser()
     subparser = parser.add_subparsers(title="commands", dest="command")
@@ -352,6 +378,10 @@ def parse_args():
     parser_backup.add_argument('subcommand', choices=['save', 'load'], help='Saves or loads a backup.')
     parser_backup.add_argument('filename', help='File to save or load the backup.')
 
+    parser_attestation = subparser.add_parser('attestation', help='Manages Enterprise Attestation')
+    parser_attestation.add_argument('subcommand', choices=['csr', 'upload'])
+    parser_attestation.add_argument('--filename', help='Uploads the certificate filename to the device as enterprise attestation certificate. If not provided, it will generate an enterprise attestation certificate automatically.')
+
     args = parser.parse_args()
     return args
 
@@ -369,9 +399,16 @@ def backup(vdr, args):
     elif (args.subcommand == 'load'):
         vdr.backup_load(args.filename)
 
+def attestation(vdr, args):
+    if (args.subcommand == 'csr'):
+        csr = x509.load_der_x509_csr(vdr.csr()[1])
+        data = urllib.parse.urlencode({'csr': csr.public_bytes(Encoding.PEM)}).encode()
+        j = get_pki_data('csr', data=data)
+        cert = x509.load_pem_x509_certificate(j['x509'].encode())
+        print(cert)
 
 def main(args):
-    print('Pico Fido Tool v1.2')
+    print('Pico Fido Tool v1.4')
     print('Author: Pol Henarejos')
     print('Report bugs to https://github.com/polhenarejos/pico-fido/issues')
     print('')
@@ -385,6 +422,8 @@ def main(args):
         secure(vdr, args)
     elif (args.command == 'backup'):
         backup(vdr, args)
+    elif (args.command == 'attestation'):
+        attestation(vdr, args)
 
 def run():
     args = parse_args()