Transaction signature bytes always use an uninitialized timestamp

[zivkovicmilos]

Description

The signature base for transactions is generated from the SignDoc structure, which has a field called Timestamp (ISO string).

This Timestamp field goes into the transaction signature bytes uninitialized (as the default value of time.Time: 0001-01-01T00:00:00Z).

gno/tm2/pkg/std/doc.go

Lines 19 to 38 in 0aaee73

	type SignDoc struct {
	ChainID string `json:"chain_id" yaml:"chain_id"`
	AccountNumber uint64 `json:"account_number" yaml:"account_number"`
	Time time.Time `json:"time" yaml:"time"`
	Sequence uint64 `json:"sequence" yaml:"sequence"`
	Fee Fee `json:"fee" yaml:"fee"`
	Msgs []Msg `json:"msgs" yaml:"msgs"`
	Memo string `json:"memo" yaml:"memo"`
	}
	// SignBytes returns the bytes to sign for a transaction.
	func SignBytes(chainID string, accountNumber uint64, sequence uint64, fee Fee, msgs []Msg, memo string) []byte {
	bz, err := amino.MarshalJSON(SignDoc{
	ChainID: chainID,
	AccountNumber: accountNumber,
	Sequence: sequence,
	Fee: fee,
	Msgs: msgs,
	Memo: memo,
	})

This means that the Timestamp for any transaction signature needs to be 0001-01-01T00:00:00Z, as the actual transaction timestamp is not read at all (doesn't go into SignDoc).

Of course, this means that any transaction signature that has a valid timestamp (different from 0001-01-01T00:00:00Z) will be considered invalid, because the gno verifier code generates the sign bytes assuming it's the default value

@moul
I'm not sure if we'd be breaking backwards compatibility by making sure the transaction sign bytes take into account the valid transaction signature timestamp instead of the default value

[moul]

Related with #1511