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This extends the recently added ECDSA signature blinding to blind DSA too.
This is based on side channel attacks demonstrated by Keegan Ryan (NCC
Group) for ECDSA which are likely to be able to be applied to DSA.
Normally, as in ECDSA, during signing the signer calculates:
s:= k^-1 * (m + r * priv_key) mod order
In ECDSA, the addition operation above provides a sufficient signal for a
flush+reload attack to derive the private key given sufficient signature
operations.
As a mitigation (based on a suggestion from Keegan) we add blinding to
the operation so that:
s := k^-1 * blind^-1 (blind * m + blind * r * priv_key) mod order
Since this attack is a localhost side channel only no CVE is assigned.
This commit also tweaks the previous ECDSA blinding so that blinding is
only removed at the last possible step.
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6523)
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Keegan Ryan (NCC Group) has demonstrated a side channel attack on an
ECDSA signature operation. During signing the signer calculates:
s:= k^-1 * (m + r * priv_key) mod order
The addition operation above provides a sufficient signal for a
flush+reload attack to derive the private key given sufficient signature
operations.
As a mitigation (based on a suggestion from Keegan) we add blinding to
the operation so that:
s := k^-1 * blind^-1 (blind * m + blind * r * priv_key) mod order
Since this attack is a localhost side channel only no CVE is assigned.
Reviewed-by: Rich Salz <rsalz@openssl.org>
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information about the length of the scalar used in ECDSA operations
from a large number (2^32) of signatures.
This doesn't rate as a CVE because:
* For the non-constant time code, there are easier ways to extract
more information.
* For the constant time code, it requires a significant number of signatures
to leak a small amount of information.
Thanks to Neals Fournaise, Eliane Jaulmes and Jean-Rene Reinhard for
reporting this issue.
Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4576)
(cherry picked from commit 4a089bbdf11f9e231cc68f42bba934c954d81a49)
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To avoid having to immediately free up r/s when setting them
don't allocate them automatically in DSA_SIG_new() and ECDSA_SIG_new().
RT#4590
Reviewed-by: Richard Levitte <levitte@openssl.org>
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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Add a flag to EC_METHOD for curves which do not support signing.
New function EC_KEY_can_sign() returns 1 is key can be used for signing.
Return an explicit error is an attempt is made to sign with
no signing curves.
Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Emilia Käsper <emilia@openssl.org>
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New functions to return internal pointer for order and cofactor. This
avoids the need to allocate a new BIGNUM which to copy the value to.
Simplify code to use new functions.
Reviewed-by: Rich Salz <rsalz@openssl.org>
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This was done by the following
find . -name '*.[ch]' | /tmp/pl
where /tmp/pl is the following three-line script:
print unless $. == 1 && m@/\* .*\.[ch] \*/@;
close ARGV if eof; # Close file to reset $.
And then some hand-editing of other files.
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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Reviewed-by: Richard Levitte <levitte@openssl.org>
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