+/* Compare two CRL extensions for delta checking purposes. They should be
+ * both present or both absent. If both present all fields must be identical.
+ */
+
+static int crl_extension_match(X509_CRL *a, X509_CRL *b, int nid)
+ {
+ ASN1_OCTET_STRING *exta, *extb;
+ int i;
+ i = X509_CRL_get_ext_by_NID(a, nid, 0);
+ if (i >= 0)
+ {
+ /* Can't have multiple occurrences */
+ if (X509_CRL_get_ext_by_NID(a, nid, i) != -1)
+ return 0;
+ exta = X509_EXTENSION_get_data(X509_CRL_get_ext(a, i));
+ }
+ else
+ exta = NULL;
+
+ i = X509_CRL_get_ext_by_NID(b, nid, 0);
+
+ if (i >= 0)
+ {
+
+ if (X509_CRL_get_ext_by_NID(b, nid, i) != -1)
+ return 0;
+ extb = X509_EXTENSION_get_data(X509_CRL_get_ext(b, i));
+ }
+ else
+ extb = NULL;
+
+ if (!exta && !extb)
+ return 1;
+
+ if (!exta || !extb)
+ return 0;
+
+
+ if (ASN1_OCTET_STRING_cmp(exta, extb))
+ return 0;
+
+ return 1;
+ }
+
+/* See if a base and delta are compatible */
+
+static int check_delta_base(X509_CRL *delta, X509_CRL *base)
+ {
+ /* Delta CRL must be a delta */
+ if (!delta->base_crl_number)
+ return 0;
+ /* Base must have a CRL number */
+ if (!base->crl_number)
+ return 0;
+ /* Issuer names must match */
+ if (X509_NAME_cmp(X509_CRL_get_issuer(base),
+ X509_CRL_get_issuer(delta)))
+ return 0;
+ /* AKID and IDP must match */
+ if (!crl_extension_match(delta, base, NID_authority_key_identifier))
+ return 0;
+ if (!crl_extension_match(delta, base, NID_issuing_distribution_point))
+ return 0;
+ /* Delta CRL base number must not exceed Full CRL number. */
+ if (ASN1_INTEGER_cmp(delta->base_crl_number, base->crl_number) > 0)
+ return 0;
+ /* Delta CRL number must exceed full CRL number */
+ if (ASN1_INTEGER_cmp(delta->crl_number, base->crl_number) > 0)
+ return 1;
+ return 0;
+ }
+
+/* For a given base CRL find a delta... maybe extend to delta scoring
+ * or retrieve a chain of deltas...
+ */
+
+static void get_delta_sk(X509_STORE_CTX *ctx, X509_CRL **dcrl, int *pscore,
+ X509_CRL *base, STACK_OF(X509_CRL) *crls)
+ {
+ X509_CRL *delta;
+ int i;
+ if (!(ctx->param->flags & X509_V_FLAG_USE_DELTAS))
+ return;
+ if (!((ctx->current_cert->ex_flags | base->flags) & EXFLAG_FRESHEST))
+ return;
+ for (i = 0; i < sk_X509_CRL_num(crls); i++)
+ {
+ delta = sk_X509_CRL_value(crls, i);
+ if (check_delta_base(delta, base))
+ {
+ if (check_crl_time(ctx, delta, 0))
+ *pscore |= CRL_SCORE_TIME_DELTA;
+ CRYPTO_add(&delta->references, 1, CRYPTO_LOCK_X509_CRL);
+ *dcrl = delta;
+ return;
+ }
+ }
+ *dcrl = NULL;
+ }
+