TLS/SSL and crypto library
13fbce17fc
The function felem_diff_128_64 in ecp_nistp521.c substracts the number |in| from |out| mod p. In order to avoid underflow it first adds 32p mod p (which is equivalent to 0 mod p) to |out|. The comments and variable naming suggest that the original author intended to add 64p mod p. In fact it has been shown that with certain unusual co-ordinates it is possible to cause an underflow in this function when only adding 32p mod p while performing a point double operation. By changing this to 64p mod p the underflow is avoided. It turns out to be quite difficult to construct points that satisfy the underflow criteria although this has been done and the underflow demonstrated. However none of these points are actually on the curve. Finding points that satisfy the underflow criteria and are also *on* the curve is considered significantly more difficult. For this reason we do not believe that this issue is currently practically exploitable and therefore no CVE has been assigned. This only impacts builds using the enable-ec_nistp_64_gcc_128 Configure option. With thanks to Bo-Yin Yang, Billy Brumley and Dr Liu for their significant help in investigating this issue. Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com> (Merged from https://github.com/openssl/openssl/pull/8405) |
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OpenSSL 3.0.0-dev
Copyright (c) 1998-2018 The OpenSSL Project
Copyright (c) 1995-1998 Eric A. Young, Tim J. Hudson
All rights reserved.
DESCRIPTION
-----------
The OpenSSL Project is a collaborative effort to develop a robust,
commercial-grade, fully featured, and Open Source toolkit implementing the
Transport Layer Security (TLS) protocols (including SSLv3) as well as a
full-strength general purpose cryptographic library.
OpenSSL is descended from the SSLeay library developed by Eric A. Young
and Tim J. Hudson.
The OpenSSL toolkit is licensed under the Apache License 2.0, which means
that you are free to get and use it for commercial and non-commercial
purposes as long as you fulfill its conditions.
OVERVIEW
--------
The OpenSSL toolkit includes:
libssl (with platform specific naming):
Provides the client and server-side implementations for SSLv3 and TLS.
libcrypto (with platform specific naming):
Provides general cryptographic and X.509 support needed by SSL/TLS but
not logically part of it.
openssl:
A command line tool that can be used for:
Creation of key parameters
Creation of X.509 certificates, CSRs and CRLs
Calculation of message digests
Encryption and decryption
SSL/TLS client and server tests
Handling of S/MIME signed or encrypted mail
And more...
INSTALLATION
------------
See the appropriate file:
INSTALL Linux, Unix, Windows, OpenVMS, ...
NOTES.* INSTALL addendums for different platforms
SUPPORT
-------
See the OpenSSL website www.openssl.org for details on how to obtain
commercial technical support. Free community support is available through the
openssl-users email list (see
https://www.openssl.org/community/mailinglists.html for further details).
If you have any problems with OpenSSL then please take the following steps
first:
- Download the latest version from the repository
to see if the problem has already been addressed
- Configure with no-asm
- Remove compiler optimization flags
If you wish to report a bug then please include the following information
and create an issue on GitHub:
- OpenSSL version: output of 'openssl version -a'
- Configuration data: output of 'perl configdata.pm --dump'
- OS Name, Version, Hardware platform
- Compiler Details (name, version)
- Application Details (name, version)
- Problem Description (steps that will reproduce the problem, if known)
- Stack Traceback (if the application dumps core)
Just because something doesn't work the way you expect does not mean it
is necessarily a bug in OpenSSL. Use the openssl-users email list for this type
of query.
HOW TO CONTRIBUTE TO OpenSSL
----------------------------
See CONTRIBUTING
LEGALITIES
----------
A number of nations restrict the use or export of cryptography. If you
are potentially subject to such restrictions you should seek competent
professional legal advice before attempting to develop or distribute
cryptographic code.