add `pkcs8_get_children()`

Signed-off-by: Steffen Jaeckel <[email protected]>

src/headers/tomcrypt_private.h

@@ -526,6 +526,9 @@ int pkcs8_decode_flexi(const unsigned char  *in,  unsigned long inlen,
                                     const void  *pwd, unsigned long pwdlen,
                                  ltc_asn1_list **decoded_list);
 
+int pkcs8_get_children(const ltc_asn1_list *decoded_list, enum ltc_oid_id *pka,
+                        ltc_asn1_list **seq, ltc_asn1_list **priv_key);
+
 #endif  /* LTC_PKCS_8 */
 
 

src/pk/asn1/pkcs8/pkcs8_get.c

@@ -0,0 +1,48 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+#include "tomcrypt_private.h"
+
+/**
+  @file pkcs8_get.c
+  PKCS#8 utility functions
+*/
+
+#ifdef LTC_PKCS_8
+
+int pkcs8_get_children(const ltc_asn1_list *decoded_list, enum ltc_oid_id *pka, ltc_asn1_list **alg_id, ltc_asn1_list **priv_key)
+{
+   int err;
+   unsigned long n;
+   der_flexi_check flexi_should[4];
+   ltc_asn1_list *seq_l, *version;
+
+   LTC_ARGCHK(ltc_mp.name != NULL);
+
+   if (alg_id == NULL) alg_id = &seq_l;
+
+   /* Setup for basic structure */
+   n=0;
+   LTC_SET_DER_FLEXI_CHECK(flexi_should, n++, LTC_ASN1_INTEGER, &version);
+   LTC_SET_DER_FLEXI_CHECK(flexi_should, n++, LTC_ASN1_SEQUENCE, alg_id);
+   LTC_SET_DER_FLEXI_CHECK(flexi_should, n++, LTC_ASN1_OCTET_STRING, priv_key);
+   LTC_SET_DER_FLEXI_CHECK(flexi_should, n, LTC_ASN1_EOL, NULL);
+
+   err = der_flexi_sequence_cmp(decoded_list, flexi_should);
+   switch (err) {
+      case CRYPT_OK:
+      case CRYPT_INPUT_TOO_LONG:
+         /* If there are attributes added after the private_key it is tagged with version 1 and
+          * we get an 'input too long' error but the rest is already decoded and can be
+          * handled the same as for version 0
+          */
+         if (mp_cmp_d(version->data, 0) != LTC_MP_EQ && mp_cmp_d(version->data, 1) != LTC_MP_EQ) {
+            return CRYPT_INVALID_PACKET;
+         }
+         break;
+      default:
+         return err;
+   }
+   return pk_get_oid_from_asn1((*alg_id)->child, pka);
+}
+
+#endif /* LTC_PKCS_8 */