The bidders sealed their numbers.
The key-holder reads them anyway.
The same tender, but bids are encrypted to the bid-openers' key instead of committed. Top left: the four firms and prices. Top right: the portal, which holds the key. Below: what they read before opening, including the leak that hands a favoured firm the contract.
Bidders
The same four firms and prices. Each bid is encrypted to the portal's key, so the key-holder can read them.
Portal & bid-openers
They hold the decryption key. These envelopes can be opened at any time; there is no time-lock.
What the bid-openers see
The key turns every envelope into a readable amount before opening day. Unlike a hash-chained board, nothing records that it was read or swapped.
This isn't hypothetical
India's e-procurement encrypts each bid to the bid-openers' RSA keys with a 2-of-N procedural quorum and no time-lock. The auditor (CAG) found the result: