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For EC keys it is particularly important to avoid leaking the bit length of the secret scalar. Key import/export should never leak the bit length of the secret scalar in the key. For this reason, on export we use padded BIGNUMs with fixed length, using the new `ossl_param_bld_push_BN_pad()`. When importing we also should make sure that, even if short lived, the newly created BIGNUM is marked with the BN_FLG_CONSTTIME flag as soon as possible, so that any processing of this BIGNUM might opt for constant time implementations in the backend. Setting the BN_FLG_CONSTTIME flag alone is never enough, we also have to preallocate the BIGNUM internal buffer to a fixed size big enough that operations performed during the processing never trigger a realloc which would leak the size of the scalar through memory accesses. Fixed length ------------ The order of the large prime subgroup of the curve is our choice for a fixed public size, as that is generally the upper bound for generating a private key in EC cryptosystems and should fit all valid secret scalars. For padding on export we just use the bit length of the order converted to bytes (rounding up). For preallocating the BIGNUM storage we look at the number of "words" required for the internal representation of the order, and we preallocate 2 extra "words" in case any of the subsequent processing might temporarily overflow the order length. Future work ----------- To ensure the flag and fixed size preallocation persists upon `EC_KEY_set_private_key()`, we need to further harden `EC_KEY_set_private_key()` and `BN_copy()`. This is done in separate commits. Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org> Reviewed-by: Shane Lontis <shane.lontis@oracle.com> (Merged from https://github.com/openssl/openssl/pull/10631) |
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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.