tdf#134041: reset engine before next digest computation

Change-Id: I68ef078f6f885bebaf29b37d5fd704a9c70c826a
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/96899
Tested-by: Jenkins
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
diff --git a/wsd/ProofKey.cpp b/wsd/ProofKey.cpp
index f3bff75..3bfaf14 100644
--- a/wsd/ProofKey.cpp
+++ b/wsd/ProofKey.cpp
@@ -243,6 +243,7 @@
{
    assert(m_pKey);
    static Poco::Crypto::RSADigestEngine digestEngine(*m_pKey, "SHA256");
    digestEngine.reset();
    digestEngine.update(proof.data(), proof.size());
    return BytesToBase64(digestEngine.signature());
}