| Description: | Normally in OpenSSL EC groups always have a co-factor present and this
is used in side channel resistant code paths. However, in some cases,
it is possible to construct a group using explicit parameters (instead
of using a named curve). In those cases it is possible that such a
group does not have the cofactor present. This can occur even where
all the parameters match a known named curve. If such a curve is used
then OpenSSL falls back to non-side channel resistant code paths which
may result in full key recovery during an ECDSA signature operation.
In order to be vulnerable an attacker would have to have the ability
to time the creation of a large number of signatures where explicit
parameters with no co-factor present are in use by an application
using libcrypto. For the avoidance of doubt libssl is not vulnerable
because explicit parameters are never used. Fixed in OpenSSL 1.1.1d
(Affected 1.1.1-1.1.1c). Fixed in OpenSSL 1.1.0l (Affected
1.1.0-1.1.0k). Fixed in OpenSSL 1.0.2t (Affected 1.0.2-1.0.2s).
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