Function open_entry 

pub fn open_entry(
    keys: &GroupKeys,
    group_id: &[u8],
    envelope_sequence_id: u64,
    sealed: &SealedCommitLogEntry,
) -> Result<PlaintextCommitLogEntry, DiscardReason>

Open an entry read from the commit-log topic of the conversation whose keys are keys and whose group id is group_id. Every length is checked first, then the signature under the conversation’s commit-log id, then the decryption. The decrypted entry must name group_id and a commit sequence id greater than 0 and below its envelope sequence id, with a valid installation signature. A failure discards this envelope only.