Plactic key agreement (insecure?)

Abstract Plactic key agreement is a new type of cryptographic key agreement that uses Knuth’s multiplication of semistandard tableaux from combinatorial algebra. The security of plactic key agreement relies on the difficulty of some computational problems, particularly the division of semistandard tableaux. Tableau division can be used to find the private key from its public key or to find the shared secret from the two exchanged public keys. Monico found a fast division algorithm, which could be a polynomial time in the length of the tableaux. Monico’s algorithm solved a challenge that had been previously estimated to cost 2128 steps to break, which is an infeasibly large number for any foreseeable computing power on earth. Monico’s algorithm solves this challenge in only a few minutes. Therefore, Monico’s attack likely makes the plactic key agreement insecure. If it were not for Monico’s attack, plactic key agreement with 1,000-byte public keys might perhaps have provided 128-bit security, with a runtime of a millisecond. But Monico’s attack breaks these public keys’ sizes in minutes.