diff --git a/Cryptlib/Pk/CryptPkcs7Verify.c b/Cryptlib/Pk/CryptPkcs7Verify.c
index dcaba43..09895d8 100644
--- a/Cryptlib/Pk/CryptPkcs7Verify.c
+++ b/Cryptlib/Pk/CryptPkcs7Verify.c
@@ -30,6 +30,91 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
 UINT8 mOidValue[9] = { 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x07, 0x02 };
 
+#if 1
+#if OPENSSL_VERSION_NUMBER < 0x10100000L
+#define X509_OBJECT_get0_X509(obj) ((obj)->data.x509)
+#define X509_OBJECT_get_type(obj) ((obj)->type)
+#define X509_STORE_CTX_get0_cert(ctx) ((ctx)->cert)
+#define X509_STORE_get0_objects(certs) ((certs)->objs)
+#define X509_get_extended_key_usage(cert) ((cert)->ex_xkusage)
+#if OPENSSL_VERSION_NUMBER < 0x10020000L
+#define X509_STORE_CTX_get0_store(ctx) ((ctx)->ctx)
+#endif
+#endif
+
+static int cert_in_store(X509 *cert, X509_STORE_CTX *ctx)
+{
+  X509_OBJECT obj;
+  obj.type = X509_LU_X509;
+  obj.data.x509 = cert;
+  return X509_OBJECT_retrieve_match(ctx->ctx->objs, &obj) != NULL;
+}
+#else
+/*
+ * Later versions of openssl will need this instead.
+ */
+static int cert_in_store(X509 *cert, X509_STORE_CTX *ctx)
+{
+  STACK_OF(X509_OBJECT) *objs;
+  X509_OBJECT *obj;
+  int i;
+
+  objs = X509_STORE_get0_objects(X509_STORE_CTX_get0_store(ctx));
+
+  for (i = 0; i < sk_X509_OBJECT_num(objs); i++) {
+    obj = sk_X509_OBJECT_value(objs, i);
+
+    if (X509_OBJECT_get_type(obj) == X509_LU_X509 &&
+	!X509_cmp(X509_OBJECT_get0_X509(obj), cert))
+      return 1;
+  }
+
+  return 0;
+}
+#endif
+
+int
+X509VerifyCb (
+  IN int            Status,
+  IN X509_STORE_CTX *Context
+  )
+{
+  INTN         Error;
+
+  Error = (INTN) X509_STORE_CTX_get_error (Context);
+
+  /* Accept code-signing keys */
+  if (Error == X509_V_ERR_INVALID_PURPOSE &&
+      X509_get_extended_key_usage(X509_STORE_CTX_get0_cert(Context)) == XKU_CODE_SIGN) {
+    Status = 1;
+  } else if (Error == X509_V_ERR_CERT_UNTRUSTED ||
+	     Error == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT ||
+	     Error == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY ||
+	     Error == X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE) {
+    /* all certs in our cert database are explicitly trusted */
+
+    if (cert_in_store(X509_STORE_CTX_get_current_cert(Context), Context))
+      Status = 1;
+  } else if (Error == X509_V_ERR_CERT_HAS_EXPIRED ||
+	     Error == X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD ||
+	     Error == X509_V_ERR_CERT_NOT_YET_VALID ||
+	     Error == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY ||
+	     Error == X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD) {
+    /* UEFI explicitly allows expired certificates */
+    Status = 1;
+#if 0
+  } else if (Error == X509_V_ERR_INVALID_CA) {
+    /* Due to the historical reason, we have to relax the the x509 v3 extension
+     * check to allow the CA certificates without the CA flag in the basic
+     * constraints or KeyCertSign in the key usage to be loaded. In the future,
+     * this callback should be removed to enforce the proper check. */
+    Status = 1;
+#endif
+  }
+
+  return Status;
+}
+
 /**
   Check input P7Data is a wrapped ContentInfo structure or not. If not construct
   a new structure to wrap P7Data.
@@ -844,6 +929,8 @@ Pkcs7Verify (
     goto _Exit;
   }
 
+  X509_STORE_set_verify_cb (CertStore, X509VerifyCb);
+
   //
   // For generic PKCS#7 handling, InData may be NULL if the content is present
   // in PKCS#7 structure. So ignore NULL checking here.