Transfers into Penumbra

IBC transfer mechanics are specified in ICS20. The FungibleTokenPacketData packet describes the transfer:

FungibleTokenPacketData {
    denomination: string,
    amount: uint256,
    sender: string,
    receiver: string,
}

The sender and receiver fields are used to specify the sending account on the source chain and the receiving account on the destination chain. However, for inbound transfers, the destination chain is Penumbra, which has no accounts. Instead, token transfers into Penumbra create an OutputDescription describing a new shielded note with the given amount and denomination, and insert an encoding of the description itself into the receiver field.