Add simple authentication to transaction proposal about safe-transaction-service

[rmeissner]

• Check how to validate that a transaction was submitted by an owner

[rmeissner]

Currently you can use a hack around it by using a random transaction hash when submitting the transaction.

@rmeissner add more info on that

[Uxio0]

API endpoints

POST /safes/{safe_address}/delegates

{
  "delegate": "<checksummed-eth-address>",
  "label": "<short-string-max-50-chars>",
  "signature": "<0x-prefixed-hex-signature>"
}

Generation of <hex-signature>

Multiple signature types are allowed:

• Contract Signature, EOA or eth_sign: The hash to sign must be keccak(checksummed-eth-address + TOTP)
• Approved Hash is not supported.

Calculation of TOTP

• TOTP will be used to prevent a repetition attack. E.g. a user signs a delegate, that delegate is compromised and removed but the signature is always valid, so another user could send that signature again to register the user as a delegate. This will prevent it.
• We will use a TOTP with T0=0 and Tx=3600 (1 hour)
• TOTP is calculated by taking the Unix epoch time (no milliseconds) and dividing by 3600 (natural division, no decimals)

Example

• We want to add the owner 0x132512f995866CcE1b0092384A6118EDaF4508Ff
• We calculate the TOTP. Current epoch=1586779140, so 1586779140 // 3600 = 440771
• We sign keccak("0x132512f995866CcE1b0092384A6118EDaF4508Ff440771")

DELETE /safes/{safe_address}/delegates/{delegate-address}

{
  "signature": "<hex-signature>"
}

Signature must be generated the same way that in POST

GET /safes/{safe_address}/delegates

{
  "delegate": "<checksummed-eth-address>",
  "delegator": "<checksummed-eth-address>", // Who added the delegate
  "label": "<short-string>"}

Notes: Endpoint will be paginated

Notes

• Every tx proposed must have a signature, so backend can check the sender. No signed txs must be discarded
• Delegates cannot add/remove delegates
• Multiple POSTs with same delegateAddress, different label and valid signature will update the label