Disclosed herein are methods, systems, and apparatus, including computer programs encoded on computer storage media, for detecting and disabling replay attacks. One of the methods includes receiving a transaction to be completed in a blockchain. A current working section of memory storing transaction information that is designated for use in identifying past transactions already processed is determined, where the memory also stores a backup section providing, when used in combination with the current working section, an alternating memory section storage scheme for the transaction information. From the current working section, whether the transaction has previously been processed is determined. When it is determined that the transaction has previously been processed, the transaction is bypassed. When it is determined that the transaction has not previously been processed the transaction is processed and transaction information for the transaction is written into the current working section.