Distributed logging for securing non-repudiable multi-party transactions

One or more tangible, non-transitory, machine-readable media storing instructions that when executed by one or more processors effectuate operations comprising:

• receiving, with one or more processors, by a responding computing system executing a software-as-a-service application, a request to the SaaS application from a requesting computing system, wherein
• the request comprises a requested action to be performed by a service of the SaaS application and a plurality of data items that are parameters of the request upon which a response to the request is to be based, and
• the SaaS application and the requesting computing system are operated by different entities in different computing domains;
• logging, with one or more processors, a first record of the received request to a first log, wherein:
• the first log is accessible for both reading and writing to both the requesting computing system and the SaaS application,
• the first log stores, for each of a plurality of previous transactions, corresponding records of previous sent-requests written by the requesting computing system and records of previous received-requests written by the SaaS application, and
• the first log is a tamper-evident log having a plurality of entries linked by cryptographic hash pointers to preceding entries;
• executing, with one or more processors, the requested action based on the parameters of the request to produce a response of the service of the SaaS application to the request;
• sending, with one or more processors, the response to the requesting computing system;
• logging, with one or more processors, a second record of the sent response to a second log of the SaaS application that is different from the first log;
• determining, with one or more processors, that the sent response matches a received version of the response by:
• accessing a third record of the received version of the response written to the first log by the requesting computing system after receiving the requesting computing system receives the sent response, and
• determining that the third record corresponds to the second record;
• and
• storing, with one or more processors, in memory, a result of the determination that the sent response matches the received version.