SQL Ledger: Cryptographically Verifiable Data in Azure SQL Database

Abstract

SQL Ledger is a new technology that allows cryptographically verifying the integrity of relational data stored in Azure SQL Database and SQL Server. This is achieved by maintaining all historical data in the database and persisting its cryptographic (SHA-256) digests in an immutable, tamper-evident ledger. Digests representing the overall state of the ledger can then be extracted and stored outside of the RDBMS to protect the data from any attacker or high privileged user, including DBAs, system and cloud administrators. The ledger and the historical data are managed transparently, offering protection without any application changes. Historical data is maintained in a relational form to support SQL queries for auditing, forensics and other purposes. SQL Ledger provides cryptographic data integrity guarantees while maintaining the power, flexibility and performance of a commercial RDBMS. In contrast to Blockchain solutions that aim for full integrity, SQL Ledger offers a form of integrity protection known as Forward Integrity. The proposed technology is significantly cheaper and more secure than traditional solutions that establish trust based on audits or mediators, but also has substantial advantages over Blockchain solutions that are complex to deploy, lack data management capabilities and suffer in terms of performance due to their decentralized nature.