openssl: crash in DTLS renegotiation after packet loss

The DTLS retransmission implementation in OpenSSL 1.0.0 before 1.0.0l and 1.0.1 before 1.0.1f does not properly maintain data structures for digest and encryption contexts, which might allow man-in-the-middle attackers to trigger the use of a different context and cause a denial of service...