NTT Seeks Blockchain Patent to Address Contract Signature Issues

Japanese telecoms group NTT seeks to implement innovative blockchain-based contracts that include both the sender’s and the receiver’s signatures.

The world’s fourth largest telecommunications provider, Japan’s Nippon Telegraph and Telephone (NTT), has applied for a blockchain patent with the US Patent and Trademark Office, in a move that could pave the way for signing mobile subscription plans on the blockchain, where they will be stored and managed in a decentralized manner.

The purpose of the application, filed earlier this month, is to create a new type of blockchain contracts that include the signatures of both the sender and the receiver. As it stands now, only the signature of the sender (or, the seller) is included.

Contract issues

One of the key benefits of blockchain is that it is immutable. This is why it is so appealing for contracts, and this is the main reason NTT wants to use the technology.

Blockchain also addresses the issue of centralized management because it’s decentralized.

In its patent application, NTT notes that blockchain-based contracts allow for the generation of a “key pair for encryption of the contract and transmits the encryption to a terminal which is its transaction sender”.

Then, this sender terminal encrypts a contract to be included in a transaction of the user of the sender terminal, using the encryption key of the receiver of the transaction.

In its patent application, NTT states:

“In contract making among two or more parties, on the other hand, a contract cannot be concluded by unilateral issuance of the contract, but must be agreed on by all the parties who are involved in the contract. However, each transaction forming a Blockchain contains only the electronic signature of the sender, and the evidence of contract agreement by the receiver is not left in the transaction.”


When blockchain is used for virtual currency, problems to be addressed include how to prove that the contract has been agreed on by two or more parties, NTT’s application notes.

Furthermore, the electronic-signature technique used in blockchains for virtual currency is built only on the electronic signature of a remitter, and does not require an electronic signature of a remittee.

The application states:

“A simple, possible way to solve this problem is to, for example, include the electronic signatures of all the involved parties in one transaction. Virtual currency employs a mechanism called multisignature, which can create an address requiring a certain number of electronic signatures or more to approve a transaction. The present invention relates particularly to a technique for leaving evidence of a contract agreed on between involved parties.”

NTT notes the procedure for including a plurality of electronic signatures in one transaction is complicated since there are many decisions to make.

These include:

  • determining which electronic signatures are needed in advance
  • how a pre-approved transaction is shared by the involved parties, and
  • where to collect a plurality of secret keys for signing.

NTT is already involved in crypto, with its IT services subsidiary NTT Data Corporation partnering with the Bank of Tokyo-Mitsubishi UFJ in a blockchain-based Proof-of-Concept (PoC) pilot whose goal is to consolidate trade links between Japan and Singapore.