nips/XX.md

NIP-XX

Improved event signing scheme

draft optional

This NIP describes a new event signature scheme that provides greater flexibility than the existing scheme by allowing signing JSONs with arbitrary properties while providing backwards compatibility. It is based on Perkeep's JSON signing. The signature scheme remains the same as the one described in NIP-01.

Signing

This NIP adds a new signature property to the event object: sig_v2. This signature is produced as follows:

1. Sign and serialize an event as described in NIP-01.
2. Remove any trailing whitespace from the serialized string such that the last element is the character }.
3. Remove the aforementioned } character.
4. Let h be the hex-encoded sha256 hash of what remains of the serialized event after steps 1 to 3.
5. Let s be the hex-encoded signature of h.
6. Append ,"sig_v2":"<s>"}, where <s> is replaced with s.

Verifying

1. Start with a serialized signed event as described above.
2. Find the last occurrence of the substring ,"sig_v2":"<s>"} in the serialized event.
3. Let h be the hex-encoded sha256 hash of the string starting from the beginning of the serialized event upto the match location (ending at the character before ,).
4. Take the string from the beggining of the serialized event upto the match location, append a single } character and parse it into a JSON object.
5. Let p be the hex-encoded pubkey provided by the JSON field pubkey of the aforementioned object.
6. Take the string starting from the match in step 3 until the end of the serialized event, replace the , character with { and parse it into a JSON object.
7. Let s be the hex-encoded signature provided by the JSON field sig_v2 of the aforementioned object.
8. Verify that s is a valid signature of h with public key p.

Backwards compatibility

Relays

Relays that don't support this NIP can either ignore or remove the unknown fields. In case they are ignored, the relay will not be able to verify that their contents have not been modified. This is not a big concern, since clients that support this NIP will be able to perform the appropriate verification on their end.

Clients

Clients that do not support this NIP can safely ignore the unknown fields. Since there are no NIPs that make use of custom fields at the time of writing, this can only impact future additions to the protocol.