Blockchain Key Exchange Using Dynamic Session Keys
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Solution Overview
Problem
In blockchain systems like Bitcoin, it is difficult to securely conceal secret information over a long term due to the permanence of transactions and the risk of secret keys being compromised, allowing unauthorized access to encrypted data.
Innovation Solution
A key exchange system utilizing ECDH key exchange and a key derivation function that generates a session key from 'related transactions' and 'a parameter of a specific block', ensuring forward secrecy and secure encryption/decryption of secret information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If public key cryptography is used to encrypt secret information in blockchain transactions, then the secret information can be securely transmitted, but the encrypted data remains vulnerable to decryption if the secret key leaks due to the permanent and unchangeable nature of blockchain transactions
Solution Approach 1:
The patent applies dynamics by making the encryption key dynamic rather than static. Instead of using a fixed secret key for encryption, the system generates a unique session key for each transaction that is derived from transaction-specific data (such as transaction hash, block hash, or other deal-specific information). This dynamic key generation ensures that even if one secret key is compromised, it cannot be used to decrypt other transactions, as each transaction uses a different derived key.
Solution Approach 2:
The patent segments the encryption process by separating the long-term secret key from the short-term session key. The secret key is stored securely in the wallet, while the session key is temporarily generated for each specific transaction. This segmentation allows the system to maintain long-term security through the secret key while achieving short-term confidentiality through the disposable session key, resolving the contradiction between permanent blockchain storage and temporary security needs.
2Ease of operation
If a fixed secret key is used for encryption, then key management is simplified, but forward secrecy is lost and all past encrypted transactions become vulnerable if the key is compromised
Solution Approach 1:
The patent applies preliminary action by pre-defining a key derivation function and the set of deal-specific information that will be used to generate session keys. The system establishes the framework for dynamic key generation in advance, so that when transactions occur, the session keys can be automatically derived without complex manual key management. This preliminary setup maintains ease of operation while enabling forward secrecy through automated session key derivation.
Solution Approach 2:
The patent introduces an intermediary element - the key derivation function - that bridges the gap between the fixed secret key and the need for dynamic session keys. The KDF acts as a mediator that takes the secret key and transaction-specific data as inputs and produces a unique session key. This intermediary mechanism automatically provides forward secrecy without requiring complex key management procedures, as the derivation process is deterministic and reproducible only by parties who know the secret key and the same transaction data.
Data Source
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AI summary
Provided are a key exchange system and a key exchange method for safely concealing secret information over a long term when the secret information is recorded on a blockchain. In a key exchange system 5, a first terminal 1 includes a license issuing unit that generates a first transaction including a first public key, a first key storage region that retains a first secret key, and a first encrypting and decrypting unit that generates a common key using deal-specific information, a second public key, and the first secret key, and a second terminal 2 includes a license requesting unit that generates a second transaction including the second public key, a second key storage region that retains a second secret key, and a second encrypting and decrypting unit that generates the common key using deal-specific information, the first public key, and the second secret key. The first encrypting and decrypting unit encrypts secret information using the common key. The second encrypting and decrypting unit decrypts the encrypted secret information using the common key.