While at university he joined the FreeBSD project, and achieved some notoriety for discovering a security weakness in Intel's hyper-threading technology.

Besides his work in delta compression and the introduction of memory-hard functions, he is also known for developing the Tarsnap online backup service, which became his full-time job.

Percival began taking mathematics courses at Simon Fraser University (SFU) at age 13, as a student at Burnaby Central Secondary School.

After a commenter on a mailing list suggested using xdelta to reduce the size of the files to be transferred, Percival began working on a more efficient delta compression algorithm.

[7] After joining the FreeBSD Security Team in 2004, Percival analyzed the behaviour of hyper-threading as then implemented on Intel's Pentium 4 CPUs.

[12] In 2009 Percival uncovered a fatal flaw in AWS' use of cryptographic signatures used to authenticate EC2, SimpleDB, SQS, and S3 REST APIs.

Drawing on his experience in distributed computing, Percival modeled an attacker using specialized hardware to massively parallelize a brute-force search for the passphrase.