Off-Chain Message Signing with the Openos CLI
Off-chain message signing is a method of signing non-transaction messages with a Openos wallet. This feature can be used to authenticate users or provide proof of wallet ownership.
Sign Off-Chain Message
To sign an arbitrary off-chain message, run the following command:
openos sign-offchain-message <MESSAGE>
The message will be encoded and signed with CLI's default private key and
signature printed to the output. If you want to sign it with another key, just
use the -k/--keypair
option:
openos sign-offchain-message -k <KEYPAIR> <MESSAGE>
By default, the messages constructed are version 0, the only version currently
supported. When other versions become available, you can override the default
value with the --version
option:
openos sign-offchain-message -k <KEYPAIR> --version <VERSION> <MESSAGE>
The message format is determined automatically based on the version and text of the message.
Version 0
headers specify three message formats allowing for trade-offs
between compatibility and composition of messages:
ID | Encoding | Maximum Length | Hardware Wallet Support |
---|---|---|---|
0 | Restricted ASCII * | 1212 | Yes |
1 | UTF-8 | 1212 | Blind sign only |
2 | UTF-8 | 65515 | No |
* Those characters for which isprint(3)
returns true. That is, 0x20..=0x7e
.
Formats 0
and 1
are motivated by hardware wallet support where both RAM to
store the payload and font character support are limited.
To sign an off-chain message with Ledger, ensure your Ledger is running latest firmware and Openos Ledger App version 1.3.0 or later. After Ledger is unlocked and Openos Ledger App is open, run:
openos sign-offchain-message -k usb://ledger <MESSAGE>
For more information on how to setup and work with the ledger device see this link.
Please note that UTF-8 encoded messages require Allow blind sign
option
enabled in Openos Ledger App. Also, due to the lack of UTF-8 support in Ledger
devices, only the hash of the message will be displayed in such cases.
If Display mode
is set to Expert
, Ledger will display technical
information about the message to be signed.
Verify Off-Chain Message Signature
To verify the off-chain message signature, run the following command:
openos verify-offchain-signature <MESSAGE> <SIGNATURE>
The public key of the default CLI signer will be used. You can specify another
key with the --signer
option:
openos verify-offchain-signature --signer <PUBKEY> <MESSAGE> <SIGNATURE>
If the signed message has a version different from the default, you need to specify the matching version explicitly:
openos verify-offchain-signature --version <VERSION> <MESSAGE> <SIGNATURE>
Protocol Specification
To ensure that off-chain messages are not valid transactions, they are encoded
with a fixed prefix: \xffopenos offchain
, where first byte is chosen such
that it is implicitly illegal as the first byte in a transaction
MessageHeader
today. More details about the payload format and other
considerations are available in the
proposal.