Public key confusion in third-party blocks

Third-party blocks can be generated without transferring the whole token to the third-party authority. Instead, a ThirdPartyBlock request can be sent, providing only the necessary info to generate a third-party block and to sign it:

• the public key of the previous block (used in the signature);
• the public keys part of the token symbol table (for public key interning in datalog expressions).

A third-party block request forged by a malicious user can trick the third-party authority into generating datalog trusting the wrong keypair.