CVE-2023-2975

Issue summary: The AES-SIV cipher implementation contains a bug that causes
it to ignore empty associated data entries which are unauthenticated as a
consequence. Impact summary: Applications that use the AES-SIV algorithm
and want to authenticate empty data entries as associated data can be
mislead by removing adding or reordering such empty entries as these are
ignored by the OpenSSL implementation. We are currently unaware of any such
applications. The AES-SIV algorithm allows for authentication of multiple
associated data entries along with the encryption. To authenticate empty
data the application has to call EVP_EncryptUpdate() (or
EVP_CipherUpdate()) with NULL pointer as the output buffer and 0 as the
input buffer length. The AES-SIV implementation in OpenSSL just returns
success for such a call instead of performing the associated data
authentication operation. The empty data thus will not be authenticated. As
this issue does not affect non-empty associated data authentication and we
expect it to be rare for an application to use empty associated data
entries this is qualified as Low severity issue.

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