X509 time: tighten validation per RFC 5280

- Reject fractional seconds
- Reject offsets
- Check that the date/time digits are in valid range.
- Add documentation for X509_cmp_time

GH issue 2620

Backported from 80770da39e

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/6182)

1 files changed, 39 insertions, 0 deletions

diff --git a/doc/man3/X509_cmp_time.pod b/doc/man3/X509_cmp_time.pod
new file mode 100644
index 0000000000..31826ad84d
--- /dev/null
+++ b/doc/man3/X509_cmp_time.pod
@@ -0,0 +1,39 @@
+=pod
+
+=head1 NAME
+
+X509_cmp_time - X509 time functions
+
+=head1 SYNOPSIS
+
+ X509_cmp_time(const ASN1_TIME *asn1_time, time_t *cmp_time);
+
+=head1 DESCRIPTION
+
+X509_cmp_time() compares the ASN1_TIME in B<asn1_time> with the time in
+<cmp_time>.
+
+B<asn1_time> must satisfy the ASN1_TIME format mandated by RFC 5280, i.e.,
+its format must be either YYMMDDHHMMSSZ or YYYYMMDDHHMMSSZ.
+
+If B<cmp_time> is NULL the current time is used.
+
+=head1 BUGS
+
+Unlike many standard comparison functions, X509_cmp_time returns 0 on error.
+
+=head1 RETURN VALUES
+
+X509_cmp_time() returns -1 if B<asn1_time> is earlier than, or equal to,
+B<cmp_time>, and 1 otherwise. It returns 0 on error.
+
+=head1 COPYRIGHT
+
+Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut